The Tor Browser: media/libpng/png.c@97036ab72558 (annotated)

media/libpng/png.c@97036ab72558 (annotated)

media/libpng/png.c

Tue, 06 Jan 2015 21:39:09 +0100

author: Michael Schloh von Bennewitz <michael@schloh.com>
date: Tue, 06 Jan 2015 21:39:09 +0100
branch: TOR_BUG_9701
changeset 8: 97036ab72558
permissions: -rw-r--r--

Conditionally force memory storage according to privacy.thirdparty.isolate;
This solves Tor bug #9701, complying with disk avoidance documented in
https://www.torproject.org/projects/torbrowser/design/#disk-avoidance.

 /* png.c - location for general purpose libpng functions
  *
  * Last changed in libpng 1.6.9 [February 6, 2014]
  * Copyright (c) 1998-2014 Glenn Randers-Pehrson
  * (Version 0.96 Copyright (c) 1996, 1997 Andreas Dilger)
  * (Version 0.88 Copyright (c) 1995, 1996 Guy Eric Schalnat, Group 42, Inc.)
  *
  * This code is released under the libpng license.
  * For conditions of distribution and use, see the disclaimer
  * and license in png.h
  */
 #include "pngpriv.h"
 /* Generate a compiler error if there is an old png.h in the search path. */
 typedef png_libpng_version_1_6_10 Your_png_h_is_not_version_1_6_10;
 /* Tells libpng that we have already handled the first "num_bytes" bytes
  * of the PNG file signature.  If the PNG data is embedded into another
  * stream we can set num_bytes = 8 so that libpng will not attempt to read
  * or write any of the magic bytes before it starts on the IHDR.
  */
 #ifdef PNG_READ_SUPPORTED
 void PNGAPI
 png_set_sig_bytes(png_structrp png_ptr, int num_bytes)
 {
    png_debug(1, "in png_set_sig_bytes");
    if (png_ptr == NULL)
       return;
    if (num_bytes > 8)
       png_error(png_ptr, "Too many bytes for PNG signature");
    png_ptr->sig_bytes = (png_byte)(num_bytes < 0 ? 0 : num_bytes);
 }
 /* Checks whether the supplied bytes match the PNG signature.  We allow
  * checking less than the full 8-byte signature so that those apps that
  * already read the first few bytes of a file to determine the file type
  * can simply check the remaining bytes for extra assurance.  Returns
  * an integer less than, equal to, or greater than zero if sig is found,
  * respectively, to be less than, to match, or be greater than the correct
  * PNG signature (this is the same behavior as strcmp, memcmp, etc).
  */
 int PNGAPI
 png_sig_cmp(png_const_bytep sig, png_size_t start, png_size_t num_to_check)
 {
    png_byte png_signature[8] = {137, 80, 78, 71, 13, 10, 26, 10};
    if (num_to_check > 8)
       num_to_check = 8;
    else if (num_to_check < 1)
       return (-1);
    if (start > 7)
       return (-1);
    if (start + num_to_check > 8)
       num_to_check = 8 - start;
    return ((int)(memcmp(&sig[start], &png_signature[start], num_to_check)));
 }
 #endif /* PNG_READ_SUPPORTED */
 #if defined(PNG_READ_SUPPORTED) || defined(PNG_WRITE_SUPPORTED)
 /* Function to allocate memory for zlib */
 PNG_FUNCTION(voidpf /* PRIVATE */,
 png_zalloc,(voidpf png_ptr, uInt items, uInt size),PNG_ALLOCATED)
 {
    png_alloc_size_t num_bytes = size;
    if (png_ptr == NULL)
       return NULL;
    if (items >= (~(png_alloc_size_t)0)/size)
    {
       png_warning (png_voidcast(png_structrp, png_ptr),
          "Potential overflow in png_zalloc()");
       return NULL;
    }
    num_bytes *= items;
    return png_malloc_warn(png_voidcast(png_structrp, png_ptr), num_bytes);
 }
 /* Function to free memory for zlib */
 void /* PRIVATE */
 png_zfree(voidpf png_ptr, voidpf ptr)
 {
    png_free(png_voidcast(png_const_structrp,png_ptr), ptr);
 }
 /* Reset the CRC variable to 32 bits of 1's.  Care must be taken
  * in case CRC is > 32 bits to leave the top bits 0.
  */
 void /* PRIVATE */
 png_reset_crc(png_structrp png_ptr)
 {
    /* The cast is safe because the crc is a 32 bit value. */
    png_ptr->crc = (png_uint_32)crc32(0, Z_NULL, 0);
 }
 /* Calculate the CRC over a section of data.  We can only pass as
  * much data to this routine as the largest single buffer size.  We
  * also check that this data will actually be used before going to the
  * trouble of calculating it.
  */
 void /* PRIVATE */
 png_calculate_crc(png_structrp png_ptr, png_const_bytep ptr, png_size_t length)
 {
    int need_crc = 1;
    if (PNG_CHUNK_ANCILLARY(png_ptr->chunk_name))
    {
       if ((png_ptr->flags & PNG_FLAG_CRC_ANCILLARY_MASK) ==
           (PNG_FLAG_CRC_ANCILLARY_USE | PNG_FLAG_CRC_ANCILLARY_NOWARN))
          need_crc = 0;
    }
    else /* critical */
    {
       if (png_ptr->flags & PNG_FLAG_CRC_CRITICAL_IGNORE)
          need_crc = 0;
    }
    /* 'uLong' is defined in zlib.h as unsigned long; this means that on some
     * systems it is a 64 bit value.  crc32, however, returns 32 bits so the
     * following cast is safe.  'uInt' may be no more than 16 bits, so it is
     * necessary to perform a loop here.
     */
    if (need_crc && length > 0)
    {
       uLong crc = png_ptr->crc; /* Should never issue a warning */
       do
       {
          uInt safe_length = (uInt)length;
          if (safe_length == 0)
             safe_length = (uInt)-1; /* evil, but safe */
          crc = crc32(crc, ptr, safe_length);
          /* The following should never issue compiler warnings; if they do the
           * target system has characteristics that will probably violate other
           * assumptions within the libpng code.
           */
          ptr += safe_length;
          length -= safe_length;
       }
       while (length > 0);
       /* And the following is always safe because the crc is only 32 bits. */
       png_ptr->crc = (png_uint_32)crc;
    }
 }
 /* Check a user supplied version number, called from both read and write
  * functions that create a png_struct.
  */
 int
 png_user_version_check(png_structrp png_ptr, png_const_charp user_png_ver)
 {
    if (user_png_ver)
    {
       int i = 0;
       do
       {
          if (user_png_ver[i] != png_libpng_ver[i])
             png_ptr->flags |= PNG_FLAG_LIBRARY_MISMATCH;
       } while (png_libpng_ver[i++]);
    }
    else
       png_ptr->flags |= PNG_FLAG_LIBRARY_MISMATCH;
    if (png_ptr->flags & PNG_FLAG_LIBRARY_MISMATCH)
    {
      /* Libpng 0.90 and later are binary incompatible with libpng 0.89, so
       * we must recompile any applications that use any older library version.
       * For versions after libpng 1.0, we will be compatible, so we need
       * only check the first and third digits (note that when we reach version
       * 1.10 we will need to check the fourth symbol, namely user_png_ver[3]).
       */
       if (user_png_ver == NULL || user_png_ver[0] != png_libpng_ver[0] ||
           (user_png_ver[0] == '1' && (user_png_ver[2] != png_libpng_ver[2] ||
           user_png_ver[3] != png_libpng_ver[3])) ||
           (user_png_ver[0] == '0' && user_png_ver[2] < '9'))
       {
 #ifdef PNG_WARNINGS_SUPPORTED
          size_t pos = 0;
          char m[128];
          pos = png_safecat(m, (sizeof m), pos,
              "Application built with libpng-");
          pos = png_safecat(m, (sizeof m), pos, user_png_ver);
          pos = png_safecat(m, (sizeof m), pos, " but running with ");
          pos = png_safecat(m, (sizeof m), pos, png_libpng_ver);
          PNG_UNUSED(pos)
          png_warning(png_ptr, m);
 #endif
 #ifdef PNG_ERROR_NUMBERS_SUPPORTED
          png_ptr->flags = 0;
 #endif
          return 0;
       }
    }
    /* Success return. */
    return 1;
 }
 /* Generic function to create a png_struct for either read or write - this
  * contains the common initialization.
  */
 PNG_FUNCTION(png_structp /* PRIVATE */,
 png_create_png_struct,(png_const_charp user_png_ver, png_voidp error_ptr,
     png_error_ptr error_fn, png_error_ptr warn_fn, png_voidp mem_ptr,
     png_malloc_ptr malloc_fn, png_free_ptr free_fn),PNG_ALLOCATED)
 {
    png_struct create_struct;
 #  ifdef PNG_SETJMP_SUPPORTED
       jmp_buf create_jmp_buf;
 #  endif
    /* This temporary stack-allocated structure is used to provide a place to
     * build enough context to allow the user provided memory allocator (if any)
     * to be called.
     */
    memset(&create_struct, 0, (sizeof create_struct));
    /* Added at libpng-1.2.6 */
 #  ifdef PNG_USER_LIMITS_SUPPORTED
       create_struct.user_width_max = PNG_USER_WIDTH_MAX;
       create_struct.user_height_max = PNG_USER_HEIGHT_MAX;
 #     ifdef PNG_USER_CHUNK_CACHE_MAX
          /* Added at libpng-1.2.43 and 1.4.0 */
          create_struct.user_chunk_cache_max = PNG_USER_CHUNK_CACHE_MAX;
 #     endif
 #     ifdef PNG_USER_CHUNK_MALLOC_MAX
          /* Added at libpng-1.2.43 and 1.4.1, required only for read but exists
           * in png_struct regardless.
           */
          create_struct.user_chunk_malloc_max = PNG_USER_CHUNK_MALLOC_MAX;
 #     endif
 #  endif
    /* The following two API calls simply set fields in png_struct, so it is safe
     * to do them now even though error handling is not yet set up.
     */
 #  ifdef PNG_USER_MEM_SUPPORTED
       png_set_mem_fn(&create_struct, mem_ptr, malloc_fn, free_fn);
 #  else
       PNG_UNUSED(mem_ptr)
       PNG_UNUSED(malloc_fn)
       PNG_UNUSED(free_fn)
 #  endif
    /* (*error_fn) can return control to the caller after the error_ptr is set,
     * this will result in a memory leak unless the error_fn does something
     * extremely sophisticated.  The design lacks merit but is implicit in the
     * API.
     */
    png_set_error_fn(&create_struct, error_ptr, error_fn, warn_fn);
 #  ifdef PNG_SETJMP_SUPPORTED
       if (!setjmp(create_jmp_buf))
       {
          /* Temporarily fake out the longjmp information until we have
           * successfully completed this function.  This only works if we have
           * setjmp() support compiled in, but it is safe - this stuff should
           * never happen.
           */
          create_struct.jmp_buf_ptr = &create_jmp_buf;
          create_struct.jmp_buf_size = 0; /*stack allocation*/
          create_struct.longjmp_fn = longjmp;
 #  else
       {
 #  endif
          /* Call the general version checker (shared with read and write code):
           */
          if (png_user_version_check(&create_struct, user_png_ver))
          {
             png_structrp png_ptr = png_voidcast(png_structrp,
                png_malloc_warn(&create_struct, (sizeof *png_ptr)));
             if (png_ptr != NULL)
             {
                /* png_ptr->zstream holds a back-pointer to the png_struct, so
                 * this can only be done now:
                 */
                create_struct.zstream.zalloc = png_zalloc;
                create_struct.zstream.zfree = png_zfree;
                create_struct.zstream.opaque = png_ptr;
 #              ifdef PNG_SETJMP_SUPPORTED
                   /* Eliminate the local error handling: */
                   create_struct.jmp_buf_ptr = NULL;
                   create_struct.jmp_buf_size = 0;
                   create_struct.longjmp_fn = 0;
 #              endif
                *png_ptr = create_struct;
                /* This is the successful return point */
                return png_ptr;
             }
          }
       }
    /* A longjmp because of a bug in the application storage allocator or a
     * simple failure to allocate the png_struct.
     */
    return NULL;
 }
 /* Allocate the memory for an info_struct for the application. */
 PNG_FUNCTION(png_infop,PNGAPI
 png_create_info_struct,(png_const_structrp png_ptr),PNG_ALLOCATED)
 {
    png_inforp info_ptr;
    png_debug(1, "in png_create_info_struct");
    if (png_ptr == NULL)
       return NULL;
    /* Use the internal API that does not (or at least should not) error out, so
     * that this call always returns ok.  The application typically sets up the
     * error handling *after* creating the info_struct because this is the way it
     * has always been done in 'example.c'.
     */
    info_ptr = png_voidcast(png_inforp, png_malloc_base(png_ptr,
       (sizeof *info_ptr)));
    if (info_ptr != NULL)
       memset(info_ptr, 0, (sizeof *info_ptr));
    return info_ptr;
 }
 /* This function frees the memory associated with a single info struct.
  * Normally, one would use either png_destroy_read_struct() or
  * png_destroy_write_struct() to free an info struct, but this may be
  * useful for some applications.  From libpng 1.6.0 this function is also used
  * internally to implement the png_info release part of the 'struct' destroy
  * APIs.  This ensures that all possible approaches free the same data (all of
  * it).
  */
 void PNGAPI
 png_destroy_info_struct(png_const_structrp png_ptr, png_infopp info_ptr_ptr)
 {
    png_inforp info_ptr = NULL;
    png_debug(1, "in png_destroy_info_struct");
    if (png_ptr == NULL)
       return;
    if (info_ptr_ptr != NULL)
       info_ptr = *info_ptr_ptr;
    if (info_ptr != NULL)
    {
       /* Do this first in case of an error below; if the app implements its own
        * memory management this can lead to png_free calling png_error, which
        * will abort this routine and return control to the app error handler.
        * An infinite loop may result if it then tries to free the same info
        * ptr.
        */
       *info_ptr_ptr = NULL;
       png_free_data(png_ptr, info_ptr, PNG_FREE_ALL, -1);
       memset(info_ptr, 0, (sizeof *info_ptr));
       png_free(png_ptr, info_ptr);
    }
 }
 /* Initialize the info structure.  This is now an internal function (0.89)
  * and applications using it are urged to use png_create_info_struct()
  * instead.  Use deprecated in 1.6.0, internal use removed (used internally it
  * is just a memset).
  *
  * NOTE: it is almost inconceivable that this API is used because it bypasses
  * the user-memory mechanism and the user error handling/warning mechanisms in
  * those cases where it does anything other than a memset.
  */
 PNG_FUNCTION(void,PNGAPI
 png_info_init_3,(png_infopp ptr_ptr, png_size_t png_info_struct_size),
    PNG_DEPRECATED)
 {
    png_inforp info_ptr = *ptr_ptr;
    png_debug(1, "in png_info_init_3");
    if (info_ptr == NULL)
       return;
    if ((sizeof (png_info)) > png_info_struct_size)
    {
       *ptr_ptr = NULL;
       /* The following line is why this API should not be used: */
       free(info_ptr);
       info_ptr = png_voidcast(png_inforp, png_malloc_base(NULL,
          (sizeof *info_ptr)));
       *ptr_ptr = info_ptr;
    }
    /* Set everything to 0 */
    memset(info_ptr, 0, (sizeof *info_ptr));
 }
 /* The following API is not called internally */
 void PNGAPI
 png_data_freer(png_const_structrp png_ptr, png_inforp info_ptr,
    int freer, png_uint_32 mask)
 {
    png_debug(1, "in png_data_freer");
    if (png_ptr == NULL || info_ptr == NULL)
       return;
    if (freer == PNG_DESTROY_WILL_FREE_DATA)
       info_ptr->free_me |= mask;
    else if (freer == PNG_USER_WILL_FREE_DATA)
       info_ptr->free_me &= ~mask;
    else
       png_error(png_ptr, "Unknown freer parameter in png_data_freer");
 }
 void PNGAPI
 png_free_data(png_const_structrp png_ptr, png_inforp info_ptr, png_uint_32 mask,
    int num)
 {
    png_debug(1, "in png_free_data");
    if (png_ptr == NULL || info_ptr == NULL)
       return;
 #ifdef PNG_TEXT_SUPPORTED
    /* Free text item num or (if num == -1) all text items */
    if ((mask & PNG_FREE_TEXT) & info_ptr->free_me)
    {
       if (num != -1)
       {
          if (info_ptr->text && info_ptr->text[num].key)
          {
             png_free(png_ptr, info_ptr->text[num].key);
             info_ptr->text[num].key = NULL;
          }
       }
       else
       {
          int i;
          for (i = 0; i < info_ptr->num_text; i++)
              png_free_data(png_ptr, info_ptr, PNG_FREE_TEXT, i);
          png_free(png_ptr, info_ptr->text);
          info_ptr->text = NULL;
          info_ptr->num_text=0;
       }
    }
 #endif
 #ifdef PNG_tRNS_SUPPORTED
    /* Free any tRNS entry */
    if ((mask & PNG_FREE_TRNS) & info_ptr->free_me)
    {
       png_free(png_ptr, info_ptr->trans_alpha);
       info_ptr->trans_alpha = NULL;
       info_ptr->valid &= ~PNG_INFO_tRNS;
    }
 #endif
 #ifdef PNG_sCAL_SUPPORTED
    /* Free any sCAL entry */
    if ((mask & PNG_FREE_SCAL) & info_ptr->free_me)
    {
       png_free(png_ptr, info_ptr->scal_s_width);
       png_free(png_ptr, info_ptr->scal_s_height);
       info_ptr->scal_s_width = NULL;
       info_ptr->scal_s_height = NULL;
       info_ptr->valid &= ~PNG_INFO_sCAL;
    }
 #endif
 #ifdef PNG_pCAL_SUPPORTED
    /* Free any pCAL entry */
    if ((mask & PNG_FREE_PCAL) & info_ptr->free_me)
    {
       png_free(png_ptr, info_ptr->pcal_purpose);
       png_free(png_ptr, info_ptr->pcal_units);
       info_ptr->pcal_purpose = NULL;
       info_ptr->pcal_units = NULL;
       if (info_ptr->pcal_params != NULL)
          {
             unsigned int i;
             for (i = 0; i < info_ptr->pcal_nparams; i++)
             {
                png_free(png_ptr, info_ptr->pcal_params[i]);
                info_ptr->pcal_params[i] = NULL;
             }
             png_free(png_ptr, info_ptr->pcal_params);
             info_ptr->pcal_params = NULL;
          }
       info_ptr->valid &= ~PNG_INFO_pCAL;
    }
 #endif
 #ifdef PNG_iCCP_SUPPORTED
    /* Free any profile entry */
    if ((mask & PNG_FREE_ICCP) & info_ptr->free_me)
    {
       png_free(png_ptr, info_ptr->iccp_name);
       png_free(png_ptr, info_ptr->iccp_profile);
       info_ptr->iccp_name = NULL;
       info_ptr->iccp_profile = NULL;
       info_ptr->valid &= ~PNG_INFO_iCCP;
    }
 #endif
 #ifdef PNG_sPLT_SUPPORTED
    /* Free a given sPLT entry, or (if num == -1) all sPLT entries */
    if ((mask & PNG_FREE_SPLT) & info_ptr->free_me)
    {
       if (num != -1)
       {
          if (info_ptr->splt_palettes)
          {
             png_free(png_ptr, info_ptr->splt_palettes[num].name);
             png_free(png_ptr, info_ptr->splt_palettes[num].entries);
             info_ptr->splt_palettes[num].name = NULL;
             info_ptr->splt_palettes[num].entries = NULL;
          }
       }
       else
       {
          if (info_ptr->splt_palettes_num)
          {
             int i;
             for (i = 0; i < info_ptr->splt_palettes_num; i++)
                png_free_data(png_ptr, info_ptr, PNG_FREE_SPLT, (int)i);
             png_free(png_ptr, info_ptr->splt_palettes);
             info_ptr->splt_palettes = NULL;
             info_ptr->splt_palettes_num = 0;
          }
          info_ptr->valid &= ~PNG_INFO_sPLT;
       }
    }
 #endif
 #ifdef PNG_STORE_UNKNOWN_CHUNKS_SUPPORTED
    if ((mask & PNG_FREE_UNKN) & info_ptr->free_me)
    {
       if (num != -1)
       {
           if (info_ptr->unknown_chunks)
           {
              png_free(png_ptr, info_ptr->unknown_chunks[num].data);
              info_ptr->unknown_chunks[num].data = NULL;
           }
       }
       else
       {
          int i;
          if (info_ptr->unknown_chunks_num)
          {
             for (i = 0; i < info_ptr->unknown_chunks_num; i++)
                png_free_data(png_ptr, info_ptr, PNG_FREE_UNKN, (int)i);
             png_free(png_ptr, info_ptr->unknown_chunks);
             info_ptr->unknown_chunks = NULL;
             info_ptr->unknown_chunks_num = 0;
          }
       }
    }
 #endif
 #ifdef PNG_hIST_SUPPORTED
    /* Free any hIST entry */
    if ((mask & PNG_FREE_HIST)  & info_ptr->free_me)
    {
       png_free(png_ptr, info_ptr->hist);
       info_ptr->hist = NULL;
       info_ptr->valid &= ~PNG_INFO_hIST;
    }
 #endif
    /* Free any PLTE entry that was internally allocated */
    if ((mask & PNG_FREE_PLTE) & info_ptr->free_me)
    {
       png_free(png_ptr, info_ptr->palette);
       info_ptr->palette = NULL;
       info_ptr->valid &= ~PNG_INFO_PLTE;
       info_ptr->num_palette = 0;
    }
 #ifdef PNG_INFO_IMAGE_SUPPORTED
    /* Free any image bits attached to the info structure */
    if ((mask & PNG_FREE_ROWS) & info_ptr->free_me)
    {
       if (info_ptr->row_pointers)
       {
          png_uint_32 row;
          for (row = 0; row < info_ptr->height; row++)
          {
             png_free(png_ptr, info_ptr->row_pointers[row]);
             info_ptr->row_pointers[row] = NULL;
          }
          png_free(png_ptr, info_ptr->row_pointers);
          info_ptr->row_pointers = NULL;
       }
       info_ptr->valid &= ~PNG_INFO_IDAT;
    }
 #endif
    if (num != -1)
       mask &= ~PNG_FREE_MUL;
    info_ptr->free_me &= ~mask;
 }
 #endif /* defined(PNG_READ_SUPPORTED) || defined(PNG_WRITE_SUPPORTED) */
 /* This function returns a pointer to the io_ptr associated with the user
  * functions.  The application should free any memory associated with this
  * pointer before png_write_destroy() or png_read_destroy() are called.
  */
 png_voidp PNGAPI
 png_get_io_ptr(png_const_structrp png_ptr)
 {
    if (png_ptr == NULL)
       return (NULL);
    return (png_ptr->io_ptr);
 }
 #if defined(PNG_READ_SUPPORTED) || defined(PNG_WRITE_SUPPORTED)
 #  ifdef PNG_STDIO_SUPPORTED
 /* Initialize the default input/output functions for the PNG file.  If you
  * use your own read or write routines, you can call either png_set_read_fn()
  * or png_set_write_fn() instead of png_init_io().  If you have defined
  * PNG_NO_STDIO or otherwise disabled PNG_STDIO_SUPPORTED, you must use a
  * function of your own because "FILE *" isn't necessarily available.
  */
 void PNGAPI
 png_init_io(png_structrp png_ptr, png_FILE_p fp)
 {
    png_debug(1, "in png_init_io");
    if (png_ptr == NULL)
       return;
    png_ptr->io_ptr = (png_voidp)fp;
 }
 #  endif
 #ifdef PNG_SAVE_INT_32_SUPPORTED
 /* The png_save_int_32 function assumes integers are stored in two's
  * complement format.  If this isn't the case, then this routine needs to
  * be modified to write data in two's complement format.  Note that,
  * the following works correctly even if png_int_32 has more than 32 bits
  * (compare the more complex code required on read for sign extension.)
  */
 void PNGAPI
 png_save_int_32(png_bytep buf, png_int_32 i)
 {
    buf[0] = (png_byte)((i >> 24) & 0xff);
    buf[1] = (png_byte)((i >> 16) & 0xff);
    buf[2] = (png_byte)((i >> 8) & 0xff);
    buf[3] = (png_byte)(i & 0xff);
 }
 #endif
 #  ifdef PNG_TIME_RFC1123_SUPPORTED
 /* Convert the supplied time into an RFC 1123 string suitable for use in
  * a "Creation Time" or other text-based time string.
  */
 int PNGAPI
 png_convert_to_rfc1123_buffer(char out[29], png_const_timep ptime)
 {
    static PNG_CONST char short_months[12][4] =
         {"Jan", "Feb", "Mar", "Apr", "May", "Jun",
          "Jul", "Aug", "Sep", "Oct", "Nov", "Dec"};
    if (out == NULL)
       return 0;
    if (ptime->year > 9999 /* RFC1123 limitation */ ||
        ptime->month == 0    ||  ptime->month > 12  ||
        ptime->day   == 0    ||  ptime->day   > 31  ||
        ptime->hour  > 23    ||  ptime->minute > 59 ||
        ptime->second > 60)
       return 0;
    {
       size_t pos = 0;
       char number_buf[5]; /* enough for a four-digit year */
 #     define APPEND_STRING(string) pos = png_safecat(out, 29, pos, (string))
 #     define APPEND_NUMBER(format, value)\
          APPEND_STRING(PNG_FORMAT_NUMBER(number_buf, format, (value)))
 #     define APPEND(ch) if (pos < 28) out[pos++] = (ch)
       APPEND_NUMBER(PNG_NUMBER_FORMAT_u, (unsigned)ptime->day);
       APPEND(' ');
       APPEND_STRING(short_months[(ptime->month - 1)]);
       APPEND(' ');
       APPEND_NUMBER(PNG_NUMBER_FORMAT_u, ptime->year);
       APPEND(' ');
       APPEND_NUMBER(PNG_NUMBER_FORMAT_02u, (unsigned)ptime->hour);
       APPEND(':');
       APPEND_NUMBER(PNG_NUMBER_FORMAT_02u, (unsigned)ptime->minute);
       APPEND(':');
       APPEND_NUMBER(PNG_NUMBER_FORMAT_02u, (unsigned)ptime->second);
       APPEND_STRING(" +0000"); /* This reliably terminates the buffer */
 #     undef APPEND
 #     undef APPEND_NUMBER
 #     undef APPEND_STRING
    }
    return 1;
 }
 #     if PNG_LIBPNG_VER < 10700
 /* To do: remove the following from libpng-1.7 */
 /* Original API that uses a private buffer in png_struct.
  * Deprecated because it causes png_struct to carry a spurious temporary
  * buffer (png_struct::time_buffer), better to have the caller pass this in.
  */
 png_const_charp PNGAPI
 png_convert_to_rfc1123(png_structrp png_ptr, png_const_timep ptime)
 {
    if (png_ptr != NULL)
    {
       /* The only failure above if png_ptr != NULL is from an invalid ptime */
       if (!png_convert_to_rfc1123_buffer(png_ptr->time_buffer, ptime))
          png_warning(png_ptr, "Ignoring invalid time value");
       else
          return png_ptr->time_buffer;
    }
    return NULL;
 }
 #     endif
 #  endif /* PNG_TIME_RFC1123_SUPPORTED */
 #endif /* defined(PNG_READ_SUPPORTED) || defined(PNG_WRITE_SUPPORTED) */
 png_const_charp PNGAPI
 png_get_copyright(png_const_structrp png_ptr)
 {
    PNG_UNUSED(png_ptr)  /* Silence compiler warning about unused png_ptr */
 #ifdef PNG_STRING_COPYRIGHT
    return PNG_STRING_COPYRIGHT
 #else
 #  ifdef __STDC__
    return PNG_STRING_NEWLINE \
      "libpng version 1.6.10 - March 6, 2014" PNG_STRING_NEWLINE \
      "Copyright (c) 1998-2014 Glenn Randers-Pehrson" PNG_STRING_NEWLINE \
      "Copyright (c) 1996-1997 Andreas Dilger" PNG_STRING_NEWLINE \
      "Copyright (c) 1995-1996 Guy Eric Schalnat, Group 42, Inc." \
      PNG_STRING_NEWLINE;
 #  else
       return "libpng version 1.6.10 - March 6, 2014\
       Copyright (c) 1998-2014 Glenn Randers-Pehrson\
       Copyright (c) 1996-1997 Andreas Dilger\
       Copyright (c) 1995-1996 Guy Eric Schalnat, Group 42, Inc.";
 #  endif
 #endif
 }
 /* The following return the library version as a short string in the
  * format 1.0.0 through 99.99.99zz.  To get the version of *.h files
  * used with your application, print out PNG_LIBPNG_VER_STRING, which
  * is defined in png.h.
  * Note: now there is no difference between png_get_libpng_ver() and
  * png_get_header_ver().  Due to the version_nn_nn_nn typedef guard,
  * it is guaranteed that png.c uses the correct version of png.h.
  */
 png_const_charp PNGAPI
 png_get_libpng_ver(png_const_structrp png_ptr)
 {
    /* Version of *.c files used when building libpng */
    return png_get_header_ver(png_ptr);
 }
 png_const_charp PNGAPI
 png_get_header_ver(png_const_structrp png_ptr)
 {
    /* Version of *.h files used when building libpng */
    PNG_UNUSED(png_ptr)  /* Silence compiler warning about unused png_ptr */
    return PNG_LIBPNG_VER_STRING;
 }
 png_const_charp PNGAPI
 png_get_header_version(png_const_structrp png_ptr)
 {
    /* Returns longer string containing both version and date */
    PNG_UNUSED(png_ptr)  /* Silence compiler warning about unused png_ptr */
 #ifdef __STDC__
    return PNG_HEADER_VERSION_STRING
 #  ifndef PNG_READ_SUPPORTED
    "     (NO READ SUPPORT)"
 #  endif
    PNG_STRING_NEWLINE;
 #else
    return PNG_HEADER_VERSION_STRING;
 #endif
 }
 #ifdef PNG_BUILD_GRAYSCALE_PALETTE_SUPPORTED
 /* NOTE: this routine is not used internally! */
 /* Build a grayscale palette.  Palette is assumed to be 1 << bit_depth
  * large of png_color.  This lets grayscale images be treated as
  * paletted.  Most useful for gamma correction and simplification
  * of code.  This API is not used internally.
  */
 void PNGAPI
 png_build_grayscale_palette(int bit_depth, png_colorp palette)
 {
    int num_palette;
    int color_inc;
    int i;
    int v;
    png_debug(1, "in png_do_build_grayscale_palette");
    if (palette == NULL)
       return;
    switch (bit_depth)
    {
       case 1:
          num_palette = 2;
          color_inc = 0xff;
          break;
       case 2:
          num_palette = 4;
          color_inc = 0x55;
          break;
       case 4:
          num_palette = 16;
          color_inc = 0x11;
          break;
       case 8:
          num_palette = 256;
          color_inc = 1;
          break;
       default:
          num_palette = 0;
          color_inc = 0;
          break;
    }
    for (i = 0, v = 0; i < num_palette; i++, v += color_inc)
    {
       palette[i].red = (png_byte)v;
       palette[i].green = (png_byte)v;
       palette[i].blue = (png_byte)v;
    }
 }
 #endif
 #ifdef PNG_SET_UNKNOWN_CHUNKS_SUPPORTED
 int PNGAPI
 png_handle_as_unknown(png_const_structrp png_ptr, png_const_bytep chunk_name)
 {
    /* Check chunk_name and return "keep" value if it's on the list, else 0 */
    png_const_bytep p, p_end;
    if (png_ptr == NULL || chunk_name == NULL || png_ptr->num_chunk_list == 0)
       return PNG_HANDLE_CHUNK_AS_DEFAULT;
    p_end = png_ptr->chunk_list;
    p = p_end + png_ptr->num_chunk_list*5; /* beyond end */
    /* The code is the fifth byte after each four byte string.  Historically this
     * code was always searched from the end of the list, this is no longer
     * necessary because the 'set' routine handles duplicate entries correcty.
     */
    do /* num_chunk_list > 0, so at least one */
    {
       p -= 5;
       if (!memcmp(chunk_name, p, 4))
          return p[4];
    }
    while (p > p_end);
    /* This means that known chunks should be processed and unknown chunks should
     * be handled according to the value of png_ptr->unknown_default; this can be
     * confusing because, as a result, there are two levels of defaulting for
     * unknown chunks.
     */
    return PNG_HANDLE_CHUNK_AS_DEFAULT;
 }
 #if defined(PNG_READ_UNKNOWN_CHUNKS_SUPPORTED) ||\
    defined(PNG_HANDLE_AS_UNKNOWN_SUPPORTED)
 int /* PRIVATE */
 png_chunk_unknown_handling(png_const_structrp png_ptr, png_uint_32 chunk_name)
 {
    png_byte chunk_string[5];
    PNG_CSTRING_FROM_CHUNK(chunk_string, chunk_name);
    return png_handle_as_unknown(png_ptr, chunk_string);
 }
 #endif /* READ_UNKNOWN_CHUNKS || HANDLE_AS_UNKNOWN */
 #endif /* SET_UNKNOWN_CHUNKS */
 #ifdef PNG_READ_SUPPORTED
 /* This function, added to libpng-1.0.6g, is untested. */
 int PNGAPI
 png_reset_zstream(png_structrp png_ptr)
 {
    if (png_ptr == NULL)
       return Z_STREAM_ERROR;
    /* WARNING: this resets the window bits to the maximum! */
    return (inflateReset(&png_ptr->zstream));
 }
 #endif /* PNG_READ_SUPPORTED */
 /* This function was added to libpng-1.0.7 */
 png_uint_32 PNGAPI
 png_access_version_number(void)
 {
    /* Version of *.c files used when building libpng */
    return((png_uint_32)PNG_LIBPNG_VER);
 }
 #if defined(PNG_READ_SUPPORTED) || defined(PNG_WRITE_SUPPORTED)
 /* Ensure that png_ptr->zstream.msg holds some appropriate error message string.
  * If it doesn't 'ret' is used to set it to something appropriate, even in cases
  * like Z_OK or Z_STREAM_END where the error code is apparently a success code.
  */
 void /* PRIVATE */
 png_zstream_error(png_structrp png_ptr, int ret)
 {
    /* Translate 'ret' into an appropriate error string, priority is given to the
     * one in zstream if set.  This always returns a string, even in cases like
     * Z_OK or Z_STREAM_END where the error code is a success code.
     */
    if (png_ptr->zstream.msg == NULL) switch (ret)
    {
       default:
       case Z_OK:
          png_ptr->zstream.msg = PNGZ_MSG_CAST("unexpected zlib return code");
          break;
       case Z_STREAM_END:
          /* Normal exit */
          png_ptr->zstream.msg = PNGZ_MSG_CAST("unexpected end of LZ stream");
          break;
       case Z_NEED_DICT:
          /* This means the deflate stream did not have a dictionary; this
           * indicates a bogus PNG.
           */
          png_ptr->zstream.msg = PNGZ_MSG_CAST("missing LZ dictionary");
          break;
       case Z_ERRNO:
          /* gz APIs only: should not happen */
          png_ptr->zstream.msg = PNGZ_MSG_CAST("zlib IO error");
          break;
       case Z_STREAM_ERROR:
          /* internal libpng error */
          png_ptr->zstream.msg = PNGZ_MSG_CAST("bad parameters to zlib");
          break;
       case Z_DATA_ERROR:
          png_ptr->zstream.msg = PNGZ_MSG_CAST("damaged LZ stream");
          break;
       case Z_MEM_ERROR:
          png_ptr->zstream.msg = PNGZ_MSG_CAST("insufficient memory");
          break;
       case Z_BUF_ERROR:
          /* End of input or output; not a problem if the caller is doing
           * incremental read or write.
           */
          png_ptr->zstream.msg = PNGZ_MSG_CAST("truncated");
          break;
       case Z_VERSION_ERROR:
          png_ptr->zstream.msg = PNGZ_MSG_CAST("unsupported zlib version");
          break;
       case PNG_UNEXPECTED_ZLIB_RETURN:
          /* Compile errors here mean that zlib now uses the value co-opted in
           * pngpriv.h for PNG_UNEXPECTED_ZLIB_RETURN; update the switch above
           * and change pngpriv.h.  Note that this message is "... return",
           * whereas the default/Z_OK one is "... return code".
           */
          png_ptr->zstream.msg = PNGZ_MSG_CAST("unexpected zlib return");
          break;
    }
 }
 /* png_convert_size: a PNGAPI but no longer in png.h, so deleted
  * at libpng 1.5.5!
  */
 /* Added at libpng version 1.2.34 and 1.4.0 (moved from pngset.c) */
 #ifdef PNG_GAMMA_SUPPORTED /* always set if COLORSPACE */
 static int
 png_colorspace_check_gamma(png_const_structrp png_ptr,
    png_colorspacerp colorspace, png_fixed_point gAMA, int from)
    /* This is called to check a new gamma value against an existing one.  The
     * routine returns false if the new gamma value should not be written.
     *
     * 'from' says where the new gamma value comes from:
     *
     *    0: the new gamma value is the libpng estimate for an ICC profile
     *    1: the new gamma value comes from a gAMA chunk
     *    2: the new gamma value comes from an sRGB chunk
     */
 {
    png_fixed_point gtest;
    if ((colorspace->flags & PNG_COLORSPACE_HAVE_GAMMA) != 0 &&
       (!png_muldiv(&gtest, colorspace->gamma, PNG_FP_1, gAMA) ||
       png_gamma_significant(gtest)))
    {
       /* Either this is an sRGB image, in which case the calculated gamma
        * approximation should match, or this is an image with a profile and the
        * value libpng calculates for the gamma of the profile does not match the
        * value recorded in the file.  The former, sRGB, case is an error, the
        * latter is just a warning.
        */
       if ((colorspace->flags & PNG_COLORSPACE_FROM_sRGB) != 0 || from == 2)
       {
          png_chunk_report(png_ptr, "gamma value does not match sRGB",
             PNG_CHUNK_ERROR);
          /* Do not overwrite an sRGB value */
          return from == 2;
       }
       else /* sRGB tag not involved */
       {
          png_chunk_report(png_ptr, "gamma value does not match libpng estimate",
             PNG_CHUNK_WARNING);
          return from == 1;
       }
    }
    return 1;
 }
 void /* PRIVATE */
 png_colorspace_set_gamma(png_const_structrp png_ptr,
    png_colorspacerp colorspace, png_fixed_point gAMA)
 {
    /* Changed in libpng-1.5.4 to limit the values to ensure overflow can't
     * occur.  Since the fixed point representation is assymetrical it is
     * possible for 1/gamma to overflow the limit of 21474 and this means the
     * gamma value must be at least 5/100000 and hence at most 20000.0.  For
     * safety the limits here are a little narrower.  The values are 0.00016 to
     * 6250.0, which are truly ridiculous gamma values (and will produce
     * displays that are all black or all white.)
     *
     * In 1.6.0 this test replaces the ones in pngrutil.c, in the gAMA chunk
     * handling code, which only required the value to be >0.
     */
    png_const_charp errmsg;
    if (gAMA < 16 || gAMA > 625000000)
       errmsg = "gamma value out of range";
 #  ifdef PNG_READ_gAMA_SUPPORTED
       /* Allow the application to set the gamma value more than once */
       else if ((png_ptr->mode & PNG_IS_READ_STRUCT) != 0 &&
          (colorspace->flags & PNG_COLORSPACE_FROM_gAMA) != 0)
          errmsg = "duplicate";
 #  endif
    /* Do nothing if the colorspace is already invalid */
    else if (colorspace->flags & PNG_COLORSPACE_INVALID)
       return;
    else
    {
       if (png_colorspace_check_gamma(png_ptr, colorspace, gAMA, 1/*from gAMA*/))
       {
          /* Store this gamma value. */
          colorspace->gamma = gAMA;
          colorspace->flags |=
             (PNG_COLORSPACE_HAVE_GAMMA | PNG_COLORSPACE_FROM_gAMA);
       }
       /* At present if the check_gamma test fails the gamma of the colorspace is
        * not updated however the colorspace is not invalidated.  This
        * corresponds to the case where the existing gamma comes from an sRGB
        * chunk or profile.  An error message has already been output.
        */
       return;
    }
    /* Error exit - errmsg has been set. */
    colorspace->flags |= PNG_COLORSPACE_INVALID;
    png_chunk_report(png_ptr, errmsg, PNG_CHUNK_WRITE_ERROR);
 }
 void /* PRIVATE */
 png_colorspace_sync_info(png_const_structrp png_ptr, png_inforp info_ptr)
 {
    if (info_ptr->colorspace.flags & PNG_COLORSPACE_INVALID)
    {
       /* Everything is invalid */
       info_ptr->valid &= ~(PNG_INFO_gAMA|PNG_INFO_cHRM|PNG_INFO_sRGB|
          PNG_INFO_iCCP);
 #     ifdef PNG_COLORSPACE_SUPPORTED
          /* Clean up the iCCP profile now if it won't be used. */
          png_free_data(png_ptr, info_ptr, PNG_FREE_ICCP, -1/*not used*/);
 #     else
          PNG_UNUSED(png_ptr)
 #     endif
    }
    else
    {
 #     ifdef PNG_COLORSPACE_SUPPORTED
          /* Leave the INFO_iCCP flag set if the pngset.c code has already set
           * it; this allows a PNG to contain a profile which matches sRGB and
           * yet still have that profile retrievable by the application.
           */
          if (info_ptr->colorspace.flags & PNG_COLORSPACE_MATCHES_sRGB)
             info_ptr->valid |= PNG_INFO_sRGB;
          else
             info_ptr->valid &= ~PNG_INFO_sRGB;
          if (info_ptr->colorspace.flags & PNG_COLORSPACE_HAVE_ENDPOINTS)
             info_ptr->valid |= PNG_INFO_cHRM;
          else
             info_ptr->valid &= ~PNG_INFO_cHRM;
 #     endif
       if (info_ptr->colorspace.flags & PNG_COLORSPACE_HAVE_GAMMA)
          info_ptr->valid |= PNG_INFO_gAMA;
       else
          info_ptr->valid &= ~PNG_INFO_gAMA;
    }
 }
 #ifdef PNG_READ_SUPPORTED
 void /* PRIVATE */
 png_colorspace_sync(png_const_structrp png_ptr, png_inforp info_ptr)
 {
    if (info_ptr == NULL) /* reduce code size; check here not in the caller */
       return;
    info_ptr->colorspace = png_ptr->colorspace;
    png_colorspace_sync_info(png_ptr, info_ptr);
 }
 #endif
 #endif
 #ifdef PNG_COLORSPACE_SUPPORTED
 /* Added at libpng-1.5.5 to support read and write of true CIEXYZ values for
  * cHRM, as opposed to using chromaticities.  These internal APIs return
  * non-zero on a parameter error.  The X, Y and Z values are required to be
  * positive and less than 1.0.
  */
 static int
 png_xy_from_XYZ(png_xy *xy, const png_XYZ *XYZ)
 {
    png_int_32 d, dwhite, whiteX, whiteY;
    d = XYZ->red_X + XYZ->red_Y + XYZ->red_Z;
    if (!png_muldiv(&xy->redx, XYZ->red_X, PNG_FP_1, d)) return 1;
    if (!png_muldiv(&xy->redy, XYZ->red_Y, PNG_FP_1, d)) return 1;
    dwhite = d;
    whiteX = XYZ->red_X;
    whiteY = XYZ->red_Y;
    d = XYZ->green_X + XYZ->green_Y + XYZ->green_Z;
    if (!png_muldiv(&xy->greenx, XYZ->green_X, PNG_FP_1, d)) return 1;
    if (!png_muldiv(&xy->greeny, XYZ->green_Y, PNG_FP_1, d)) return 1;
    dwhite += d;
    whiteX += XYZ->green_X;
    whiteY += XYZ->green_Y;
    d = XYZ->blue_X + XYZ->blue_Y + XYZ->blue_Z;
    if (!png_muldiv(&xy->bluex, XYZ->blue_X, PNG_FP_1, d)) return 1;
    if (!png_muldiv(&xy->bluey, XYZ->blue_Y, PNG_FP_1, d)) return 1;
    dwhite += d;
    whiteX += XYZ->blue_X;
    whiteY += XYZ->blue_Y;
    /* The reference white is simply the sum of the end-point (X,Y,Z) vectors,
     * thus:
     */
    if (!png_muldiv(&xy->whitex, whiteX, PNG_FP_1, dwhite)) return 1;
    if (!png_muldiv(&xy->whitey, whiteY, PNG_FP_1, dwhite)) return 1;
    return 0;
 }
 static int
 png_XYZ_from_xy(png_XYZ *XYZ, const png_xy *xy)
 {
    png_fixed_point red_inverse, green_inverse, blue_scale;
    png_fixed_point left, right, denominator;
    /* Check xy and, implicitly, z.  Note that wide gamut color spaces typically
     * have end points with 0 tristimulus values (these are impossible end
     * points, but they are used to cover the possible colors.)
     */
    if (xy->redx < 0 || xy->redx > PNG_FP_1) return 1;
    if (xy->redy < 0 || xy->redy > PNG_FP_1-xy->redx) return 1;
    if (xy->greenx < 0 || xy->greenx > PNG_FP_1) return 1;
    if (xy->greeny < 0 || xy->greeny > PNG_FP_1-xy->greenx) return 1;
    if (xy->bluex < 0 || xy->bluex > PNG_FP_1) return 1;
    if (xy->bluey < 0 || xy->bluey > PNG_FP_1-xy->bluex) return 1;
    if (xy->whitex < 0 || xy->whitex > PNG_FP_1) return 1;
    if (xy->whitey < 0 || xy->whitey > PNG_FP_1-xy->whitex) return 1;
    /* The reverse calculation is more difficult because the original tristimulus
     * value had 9 independent values (red,green,blue)x(X,Y,Z) however only 8
     * derived values were recorded in the cHRM chunk;
     * (red,green,blue,white)x(x,y).  This loses one degree of freedom and
     * therefore an arbitrary ninth value has to be introduced to undo the
     * original transformations.
     *
     * Think of the original end-points as points in (X,Y,Z) space.  The
     * chromaticity values (c) have the property:
     *
     *           C
     *   c = ---------
     *       X + Y + Z
     *
     * For each c (x,y,z) from the corresponding original C (X,Y,Z).  Thus the
     * three chromaticity values (x,y,z) for each end-point obey the
     * relationship:
     *
     *   x + y + z = 1
     *
     * This describes the plane in (X,Y,Z) space that intersects each axis at the
     * value 1.0; call this the chromaticity plane.  Thus the chromaticity
     * calculation has scaled each end-point so that it is on the x+y+z=1 plane
     * and chromaticity is the intersection of the vector from the origin to the
     * (X,Y,Z) value with the chromaticity plane.
     *
     * To fully invert the chromaticity calculation we would need the three
     * end-point scale factors, (red-scale, green-scale, blue-scale), but these
     * were not recorded.  Instead we calculated the reference white (X,Y,Z) and
     * recorded the chromaticity of this.  The reference white (X,Y,Z) would have
     * given all three of the scale factors since:
     *
     *    color-C = color-c * color-scale
     *    white-C = red-C + green-C + blue-C
     *            = red-c*red-scale + green-c*green-scale + blue-c*blue-scale
     *
     * But cHRM records only white-x and white-y, so we have lost the white scale
     * factor:
     *
     *    white-C = white-c*white-scale
     *
     * To handle this the inverse transformation makes an arbitrary assumption
     * about white-scale:
     *
     *    Assume: white-Y = 1.0
     *    Hence:  white-scale = 1/white-y
     *    Or:     red-Y + green-Y + blue-Y = 1.0
     *
     * Notice the last statement of the assumption gives an equation in three of
     * the nine values we want to calculate.  8 more equations come from the
     * above routine as summarised at the top above (the chromaticity
     * calculation):
     *
     *    Given: color-x = color-X / (color-X + color-Y + color-Z)
     *    Hence: (color-x - 1)*color-X + color.x*color-Y + color.x*color-Z = 0
     *
     * This is 9 simultaneous equations in the 9 variables "color-C" and can be
     * solved by Cramer's rule.  Cramer's rule requires calculating 10 9x9 matrix
     * determinants, however this is not as bad as it seems because only 28 of
     * the total of 90 terms in the various matrices are non-zero.  Nevertheless
     * Cramer's rule is notoriously numerically unstable because the determinant
     * calculation involves the difference of large, but similar, numbers.  It is
     * difficult to be sure that the calculation is stable for real world values
     * and it is certain that it becomes unstable where the end points are close
     * together.
     *
     * So this code uses the perhaps slightly less optimal but more
     * understandable and totally obvious approach of calculating color-scale.
     *
     * This algorithm depends on the precision in white-scale and that is
     * (1/white-y), so we can immediately see that as white-y approaches 0 the
     * accuracy inherent in the cHRM chunk drops off substantially.
     *
     * libpng arithmetic: a simple invertion of the above equations
     * ------------------------------------------------------------
     *
     *    white_scale = 1/white-y
     *    white-X = white-x * white-scale
     *    white-Y = 1.0
     *    white-Z = (1 - white-x - white-y) * white_scale
     *
     *    white-C = red-C + green-C + blue-C
     *            = red-c*red-scale + green-c*green-scale + blue-c*blue-scale
     *
     * This gives us three equations in (red-scale,green-scale,blue-scale) where
     * all the coefficients are now known:
     *
     *    red-x*red-scale + green-x*green-scale + blue-x*blue-scale
     *       = white-x/white-y
     *    red-y*red-scale + green-y*green-scale + blue-y*blue-scale = 1
     *    red-z*red-scale + green-z*green-scale + blue-z*blue-scale
     *       = (1 - white-x - white-y)/white-y
     *
     * In the last equation color-z is (1 - color-x - color-y) so we can add all
     * three equations together to get an alternative third:
     *
     *    red-scale + green-scale + blue-scale = 1/white-y = white-scale
     *
     * So now we have a Cramer's rule solution where the determinants are just
     * 3x3 - far more tractible.  Unfortunately 3x3 determinants still involve
     * multiplication of three coefficients so we can't guarantee to avoid
     * overflow in the libpng fixed point representation.  Using Cramer's rule in
     * floating point is probably a good choice here, but it's not an option for
     * fixed point.  Instead proceed to simplify the first two equations by
     * eliminating what is likely to be the largest value, blue-scale:
     *
     *    blue-scale = white-scale - red-scale - green-scale
     *
     * Hence:
     *
     *    (red-x - blue-x)*red-scale + (green-x - blue-x)*green-scale =
     *                (white-x - blue-x)*white-scale
     *
     *    (red-y - blue-y)*red-scale + (green-y - blue-y)*green-scale =
     *                1 - blue-y*white-scale
     *
     * And now we can trivially solve for (red-scale,green-scale):
     *
     *    green-scale =
     *                (white-x - blue-x)*white-scale - (red-x - blue-x)*red-scale
     *                -----------------------------------------------------------
     *                                  green-x - blue-x
     *
     *    red-scale =
     *                1 - blue-y*white-scale - (green-y - blue-y) * green-scale
     *                ---------------------------------------------------------
     *                                  red-y - blue-y
     *
     * Hence:
     *
     *    red-scale =
     *          ( (green-x - blue-x) * (white-y - blue-y) -
     *            (green-y - blue-y) * (white-x - blue-x) ) / white-y
     * -------------------------------------------------------------------------
     *  (green-x - blue-x)*(red-y - blue-y)-(green-y - blue-y)*(red-x - blue-x)
     *
     *    green-scale =
     *          ( (red-y - blue-y) * (white-x - blue-x) -
     *            (red-x - blue-x) * (white-y - blue-y) ) / white-y
     * -------------------------------------------------------------------------
     *  (green-x - blue-x)*(red-y - blue-y)-(green-y - blue-y)*(red-x - blue-x)
     *
     * Accuracy:
     * The input values have 5 decimal digits of accuracy.  The values are all in
     * the range 0 < value < 1, so simple products are in the same range but may
     * need up to 10 decimal digits to preserve the original precision and avoid
     * underflow.  Because we are using a 32-bit signed representation we cannot
     * match this; the best is a little over 9 decimal digits, less than 10.
     *
     * The approach used here is to preserve the maximum precision within the
     * signed representation.  Because the red-scale calculation above uses the
     * difference between two products of values that must be in the range -1..+1
     * it is sufficient to divide the product by 7; ceil(100,000/32767*2).  The
     * factor is irrelevant in the calculation because it is applied to both
     * numerator and denominator.
     *
     * Note that the values of the differences of the products of the
     * chromaticities in the above equations tend to be small, for example for
     * the sRGB chromaticities they are:
     *
     * red numerator:    -0.04751
     * green numerator:  -0.08788
     * denominator:      -0.2241 (without white-y multiplication)
     *
     *  The resultant Y coefficients from the chromaticities of some widely used
     *  color space definitions are (to 15 decimal places):
     *
     *  sRGB
     *    0.212639005871510 0.715168678767756 0.072192315360734
     *  Kodak ProPhoto
     *    0.288071128229293 0.711843217810102 0.000085653960605
     *  Adobe RGB
     *    0.297344975250536 0.627363566255466 0.075291458493998
     *  Adobe Wide Gamut RGB
     *    0.258728243040113 0.724682314948566 0.016589442011321
     */
    /* By the argument, above overflow should be impossible here. The return
     * value of 2 indicates an internal error to the caller.
     */
    if (!png_muldiv(&left, xy->greenx-xy->bluex, xy->redy - xy->bluey, 7))
       return 2;
    if (!png_muldiv(&right, xy->greeny-xy->bluey, xy->redx - xy->bluex, 7))
       return 2;
    denominator = left - right;
    /* Now find the red numerator. */
    if (!png_muldiv(&left, xy->greenx-xy->bluex, xy->whitey-xy->bluey, 7))
       return 2;
    if (!png_muldiv(&right, xy->greeny-xy->bluey, xy->whitex-xy->bluex, 7))
       return 2;
    /* Overflow is possible here and it indicates an extreme set of PNG cHRM
     * chunk values.  This calculation actually returns the reciprocal of the
     * scale value because this allows us to delay the multiplication of white-y
     * into the denominator, which tends to produce a small number.
     */
    if (!png_muldiv(&red_inverse, xy->whitey, denominator, left-right) ||
        red_inverse <= xy->whitey /* r+g+b scales = white scale */)
       return 1;
    /* Similarly for green_inverse: */
    if (!png_muldiv(&left, xy->redy-xy->bluey, xy->whitex-xy->bluex, 7))
       return 2;
    if (!png_muldiv(&right, xy->redx-xy->bluex, xy->whitey-xy->bluey, 7))
       return 2;
    if (!png_muldiv(&green_inverse, xy->whitey, denominator, left-right) ||
        green_inverse <= xy->whitey)
       return 1;
    /* And the blue scale, the checks above guarantee this can't overflow but it
     * can still produce 0 for extreme cHRM values.
     */
    blue_scale = png_reciprocal(xy->whitey) - png_reciprocal(red_inverse) -
       png_reciprocal(green_inverse);
    if (blue_scale <= 0) return 1;
    /* And fill in the png_XYZ: */
    if (!png_muldiv(&XYZ->red_X, xy->redx, PNG_FP_1, red_inverse)) return 1;
    if (!png_muldiv(&XYZ->red_Y, xy->redy, PNG_FP_1, red_inverse)) return 1;
    if (!png_muldiv(&XYZ->red_Z, PNG_FP_1 - xy->redx - xy->redy, PNG_FP_1,
       red_inverse))
       return 1;
    if (!png_muldiv(&XYZ->green_X, xy->greenx, PNG_FP_1, green_inverse))
       return 1;
    if (!png_muldiv(&XYZ->green_Y, xy->greeny, PNG_FP_1, green_inverse))
       return 1;
    if (!png_muldiv(&XYZ->green_Z, PNG_FP_1 - xy->greenx - xy->greeny, PNG_FP_1,
       green_inverse))
       return 1;
    if (!png_muldiv(&XYZ->blue_X, xy->bluex, blue_scale, PNG_FP_1)) return 1;
    if (!png_muldiv(&XYZ->blue_Y, xy->bluey, blue_scale, PNG_FP_1)) return 1;
    if (!png_muldiv(&XYZ->blue_Z, PNG_FP_1 - xy->bluex - xy->bluey, blue_scale,
       PNG_FP_1))
       return 1;
    return 0; /*success*/
 }
 static int
 png_XYZ_normalize(png_XYZ *XYZ)
 {
    png_int_32 Y;
    if (XYZ->red_Y < 0 || XYZ->green_Y < 0 || XYZ->blue_Y < 0 ||
       XYZ->red_X < 0 || XYZ->green_X < 0 || XYZ->blue_X < 0 ||
       XYZ->red_Z < 0 || XYZ->green_Z < 0 || XYZ->blue_Z < 0)
       return 1;
    /* Normalize by scaling so the sum of the end-point Y values is PNG_FP_1.
     * IMPLEMENTATION NOTE: ANSI requires signed overflow not to occur, therefore
     * relying on addition of two positive values producing a negative one is not
     * safe.
     */
    Y = XYZ->red_Y;
    if (0x7fffffff - Y < XYZ->green_X) return 1;
    Y += XYZ->green_Y;
    if (0x7fffffff - Y < XYZ->blue_X) return 1;
    Y += XYZ->blue_Y;
    if (Y != PNG_FP_1)
    {
       if (!png_muldiv(&XYZ->red_X, XYZ->red_X, PNG_FP_1, Y)) return 1;
       if (!png_muldiv(&XYZ->red_Y, XYZ->red_Y, PNG_FP_1, Y)) return 1;
       if (!png_muldiv(&XYZ->red_Z, XYZ->red_Z, PNG_FP_1, Y)) return 1;
       if (!png_muldiv(&XYZ->green_X, XYZ->green_X, PNG_FP_1, Y)) return 1;
       if (!png_muldiv(&XYZ->green_Y, XYZ->green_Y, PNG_FP_1, Y)) return 1;
       if (!png_muldiv(&XYZ->green_Z, XYZ->green_Z, PNG_FP_1, Y)) return 1;
       if (!png_muldiv(&XYZ->blue_X, XYZ->blue_X, PNG_FP_1, Y)) return 1;
       if (!png_muldiv(&XYZ->blue_Y, XYZ->blue_Y, PNG_FP_1, Y)) return 1;
       if (!png_muldiv(&XYZ->blue_Z, XYZ->blue_Z, PNG_FP_1, Y)) return 1;
    }
    return 0;
 }
 static int
 png_colorspace_endpoints_match(const png_xy *xy1, const png_xy *xy2, int delta)
 {
    /* Allow an error of +/-0.01 (absolute value) on each chromaticity */
    return !(PNG_OUT_OF_RANGE(xy1->whitex, xy2->whitex,delta) ||
       PNG_OUT_OF_RANGE(xy1->whitey, xy2->whitey,delta) ||
       PNG_OUT_OF_RANGE(xy1->redx,   xy2->redx,  delta) ||
       PNG_OUT_OF_RANGE(xy1->redy,   xy2->redy,  delta) ||
       PNG_OUT_OF_RANGE(xy1->greenx, xy2->greenx,delta) ||
       PNG_OUT_OF_RANGE(xy1->greeny, xy2->greeny,delta) ||
       PNG_OUT_OF_RANGE(xy1->bluex,  xy2->bluex, delta) ||
       PNG_OUT_OF_RANGE(xy1->bluey,  xy2->bluey, delta));
 }
 /* Added in libpng-1.6.0, a different check for the validity of a set of cHRM
  * chunk chromaticities.  Earlier checks used to simply look for the overflow
  * condition (where the determinant of the matrix to solve for XYZ ends up zero
  * because the chromaticity values are not all distinct.)  Despite this it is
  * theoretically possible to produce chromaticities that are apparently valid
  * but that rapidly degrade to invalid, potentially crashing, sets because of
  * arithmetic inaccuracies when calculations are performed on them.  The new
  * check is to round-trip xy -> XYZ -> xy and then check that the result is
  * within a small percentage of the original.
  */
 static int
 png_colorspace_check_xy(png_XYZ *XYZ, const png_xy *xy)
 {
    int result;
    png_xy xy_test;
    /* As a side-effect this routine also returns the XYZ endpoints. */
    result = png_XYZ_from_xy(XYZ, xy);
    if (result) return result;
    result = png_xy_from_XYZ(&xy_test, XYZ);
    if (result) return result;
    if (png_colorspace_endpoints_match(xy, &xy_test,
 /*actually, the math is pretty accurate*/))
       return 0;
    /* Too much slip */
    return 1;
 }
 /* This is the check going the other way.  The XYZ is modified to normalize it
  * (another side-effect) and the xy chromaticities are returned.
  */
 static int
 png_colorspace_check_XYZ(png_xy *xy, png_XYZ *XYZ)
 {
    int result;
    png_XYZ XYZtemp;
    result = png_XYZ_normalize(XYZ);
    if (result) return result;
    result = png_xy_from_XYZ(xy, XYZ);
    if (result) return result;
    XYZtemp = *XYZ;
    return png_colorspace_check_xy(&XYZtemp, xy);
 }
 /* Used to check for an endpoint match against sRGB */
 static const png_xy sRGB_xy = /* From ITU-R BT.709-3 */
 {
    /* color      x       y */
    /* red   */ 64000, 33000,
    /* green */ 30000, 60000,
    /* blue  */ 15000,  6000,
    /* white */ 31270, 32900
 };
 static int
 png_colorspace_set_xy_and_XYZ(png_const_structrp png_ptr,
    png_colorspacerp colorspace, const png_xy *xy, const png_XYZ *XYZ,
    int preferred)
 {
    if (colorspace->flags & PNG_COLORSPACE_INVALID)
       return 0;
    /* The consistency check is performed on the chromaticities; this factors out
     * variations because of the normalization (or not) of the end point Y
     * values.
     */
    if (preferred < 2 && (colorspace->flags & PNG_COLORSPACE_HAVE_ENDPOINTS))
    {
       /* The end points must be reasonably close to any we already have.  The
        * following allows an error of up to +/-.001
        */
       if (!png_colorspace_endpoints_match(xy, &colorspace->end_points_xy, 100))
       {
          colorspace->flags |= PNG_COLORSPACE_INVALID;
          png_benign_error(png_ptr, "inconsistent chromaticities");
          return 0; /* failed */
       }
       /* Only overwrite with preferred values */
       if (!preferred)
          return 1; /* ok, but no change */
    }
    colorspace->end_points_xy = *xy;
    colorspace->end_points_XYZ = *XYZ;
    colorspace->flags |= PNG_COLORSPACE_HAVE_ENDPOINTS;
    /* The end points are normally quoted to two decimal digits, so allow +/-0.01
     * on this test.
     */
    if (png_colorspace_endpoints_match(xy, &sRGB_xy, 1000))
       colorspace->flags |= PNG_COLORSPACE_ENDPOINTS_MATCH_sRGB;
    else
       colorspace->flags &= PNG_COLORSPACE_CANCEL(
          PNG_COLORSPACE_ENDPOINTS_MATCH_sRGB);
    return 2; /* ok and changed */
 }
 int /* PRIVATE */
 png_colorspace_set_chromaticities(png_const_structrp png_ptr,
    png_colorspacerp colorspace, const png_xy *xy, int preferred)
 {
    /* We must check the end points to ensure they are reasonable - in the past
     * color management systems have crashed as a result of getting bogus
     * colorant values, while this isn't the fault of libpng it is the
     * responsibility of libpng because PNG carries the bomb and libpng is in a
     * position to protect against it.
     */
    png_XYZ XYZ;
    switch (png_colorspace_check_xy(&XYZ, xy))
    {
       case 0: /* success */
          return png_colorspace_set_xy_and_XYZ(png_ptr, colorspace, xy, &XYZ,
             preferred);
       case 1:
          /* We can't invert the chromaticities so we can't produce value XYZ
           * values.  Likely as not a color management system will fail too.
           */
          colorspace->flags |= PNG_COLORSPACE_INVALID;
          png_benign_error(png_ptr, "invalid chromaticities");
          break;
       default:
          /* libpng is broken; this should be a warning but if it happens we
           * want error reports so for the moment it is an error.
           */
          colorspace->flags |= PNG_COLORSPACE_INVALID;
          png_error(png_ptr, "internal error checking chromaticities");
          break;
    }
    return 0; /* failed */
 }
 int /* PRIVATE */
 png_colorspace_set_endpoints(png_const_structrp png_ptr,
    png_colorspacerp colorspace, const png_XYZ *XYZ_in, int preferred)
 {
    png_XYZ XYZ = *XYZ_in;
    png_xy xy;
    switch (png_colorspace_check_XYZ(&xy, &XYZ))
    {
       case 0:
          return png_colorspace_set_xy_and_XYZ(png_ptr, colorspace, &xy, &XYZ,
             preferred);
       case 1:
          /* End points are invalid. */
          colorspace->flags |= PNG_COLORSPACE_INVALID;
          png_benign_error(png_ptr, "invalid end points");
          break;
       default:
          colorspace->flags |= PNG_COLORSPACE_INVALID;
          png_error(png_ptr, "internal error checking chromaticities");
          break;
    }
    return 0; /* failed */
 }
 #if defined(PNG_sRGB_SUPPORTED) || defined(PNG_iCCP_SUPPORTED)
 /* Error message generation */
 static char
 png_icc_tag_char(png_uint_32 byte)
 {
    byte &= 0xff;
    if (byte >= 32 && byte <= 126)
       return (char)byte;
    else
       return '?';
 }
 static void
 png_icc_tag_name(char *name, png_uint_32 tag)
 {
    name[0] = '\'';
    name[1] = png_icc_tag_char(tag >> 24);
    name[2] = png_icc_tag_char(tag >> 16);
    name[3] = png_icc_tag_char(tag >>  8);
    name[4] = png_icc_tag_char(tag      );
    name[5] = '\'';
 }
 static int
 is_ICC_signature_char(png_alloc_size_t it)
 {
    return it == 32 || (it >= 48 && it <= 57) || (it >= 65 && it <= 90) ||
       (it >= 97 && it <= 122);
 }
 static int
 is_ICC_signature(png_alloc_size_t it)
 {
    return is_ICC_signature_char(it >> 24) /* checks all the top bits */ &&
       is_ICC_signature_char((it >> 16) & 0xff) &&
       is_ICC_signature_char((it >> 8) & 0xff) &&
       is_ICC_signature_char(it & 0xff);
 }
 static int
 png_icc_profile_error(png_const_structrp png_ptr, png_colorspacerp colorspace,
    png_const_charp name, png_alloc_size_t value, png_const_charp reason)
 {
    size_t pos;
    char message[196]; /* see below for calculation */
    if (colorspace != NULL)
       colorspace->flags |= PNG_COLORSPACE_INVALID;
    pos = png_safecat(message, (sizeof message), 0, "profile '"); /* 9 chars */
    pos = png_safecat(message, pos+79, pos, name); /* Truncate to 79 chars */
    pos = png_safecat(message, (sizeof message), pos, "': "); /* +2 = 90 */
    if (is_ICC_signature(value))
    {
       /* So 'value' is at most 4 bytes and the following cast is safe */
       png_icc_tag_name(message+pos, (png_uint_32)value);
       pos += 6; /* total +8; less than the else clause */
       message[pos++] = ':';
       message[pos++] = ' ';
    }
 #  ifdef PNG_WARNINGS_SUPPORTED
    else
       {
          char number[PNG_NUMBER_BUFFER_SIZE]; /* +24 = 114*/
          pos = png_safecat(message, (sizeof message), pos,
             png_format_number(number, number+(sizeof number),
                PNG_NUMBER_FORMAT_x, value));
          pos = png_safecat(message, (sizeof message), pos, "h: "); /*+2 = 116*/
       }
 #  endif
    /* The 'reason' is an arbitrary message, allow +79 maximum 195 */
    pos = png_safecat(message, (sizeof message), pos, reason);
    PNG_UNUSED(pos)
    /* This is recoverable, but make it unconditionally an app_error on write to
     * avoid writing invalid ICC profiles into PNG files.  (I.e.  we handle them
     * on read, with a warning, but on write unless the app turns off
     * application errors the PNG won't be written.)
     */
    png_chunk_report(png_ptr, message,
       (colorspace != NULL) ? PNG_CHUNK_ERROR : PNG_CHUNK_WRITE_ERROR);
    return 0;
 }
 #endif /* sRGB || iCCP */
 #ifdef PNG_sRGB_SUPPORTED
 int /* PRIVATE */
 png_colorspace_set_sRGB(png_const_structrp png_ptr, png_colorspacerp colorspace,
    int intent)
 {
    /* sRGB sets known gamma, end points and (from the chunk) intent. */
    /* IMPORTANT: these are not necessarily the values found in an ICC profile
     * because ICC profiles store values adapted to a D50 environment; it is
     * expected that the ICC profile mediaWhitePointTag will be D50, see the
     * checks and code elsewhere to understand this better.
     *
     * These XYZ values, which are accurate to 5dp, produce rgb to gray
     * coefficients of (6968,23435,2366), which are reduced (because they add up
     * to 32769 not 32768) to (6968,23434,2366).  These are the values that
     * libpng has traditionally used (and are the best values given the 15bit
     * algorithm used by the rgb to gray code.)
     */
    static const png_XYZ sRGB_XYZ = /* D65 XYZ (*not* the D50 adapted values!) */
    {
       /* color      X      Y      Z */
       /* red   */ 41239, 21264,  1933,
       /* green */ 35758, 71517, 11919,
       /* blue  */ 18048,  7219, 95053
    };
    /* Do nothing if the colorspace is already invalidated. */
    if (colorspace->flags & PNG_COLORSPACE_INVALID)
       return 0;
    /* Check the intent, then check for existing settings.  It is valid for the
     * PNG file to have cHRM or gAMA chunks along with sRGB, but the values must
     * be consistent with the correct values.  If, however, this function is
     * called below because an iCCP chunk matches sRGB then it is quite
     * conceivable that an older app recorded incorrect gAMA and cHRM because of
     * an incorrect calculation based on the values in the profile - this does
     * *not* invalidate the profile (though it still produces an error, which can
     * be ignored.)
     */
    if (intent < 0 || intent >= PNG_sRGB_INTENT_LAST)
       return png_icc_profile_error(png_ptr, colorspace, "sRGB",
          (unsigned)intent, "invalid sRGB rendering intent");
    if ((colorspace->flags & PNG_COLORSPACE_HAVE_INTENT) != 0 &&
       colorspace->rendering_intent != intent)
       return png_icc_profile_error(png_ptr, colorspace, "sRGB",
          (unsigned)intent, "inconsistent rendering intents");
    if ((colorspace->flags & PNG_COLORSPACE_FROM_sRGB) != 0)
    {
       png_benign_error(png_ptr, "duplicate sRGB information ignored");
       return 0;
    }
    /* If the standard sRGB cHRM chunk does not match the one from the PNG file
     * warn but overwrite the value with the correct one.
     */
    if ((colorspace->flags & PNG_COLORSPACE_HAVE_ENDPOINTS) != 0 &&
       !png_colorspace_endpoints_match(&sRGB_xy, &colorspace->end_points_xy,
 ))
       png_chunk_report(png_ptr, "cHRM chunk does not match sRGB",
          PNG_CHUNK_ERROR);
    /* This check is just done for the error reporting - the routine always
     * returns true when the 'from' argument corresponds to sRGB (2).
     */
    (void)png_colorspace_check_gamma(png_ptr, colorspace, PNG_GAMMA_sRGB_INVERSE,
 /*from sRGB*/);
    /* intent: bugs in GCC force 'int' to be used as the parameter type. */
    colorspace->rendering_intent = (png_uint_16)intent;
    colorspace->flags |= PNG_COLORSPACE_HAVE_INTENT;
    /* endpoints */
    colorspace->end_points_xy = sRGB_xy;
    colorspace->end_points_XYZ = sRGB_XYZ;
    colorspace->flags |=
       (PNG_COLORSPACE_HAVE_ENDPOINTS|PNG_COLORSPACE_ENDPOINTS_MATCH_sRGB);
    /* gamma */
    colorspace->gamma = PNG_GAMMA_sRGB_INVERSE;
    colorspace->flags |= PNG_COLORSPACE_HAVE_GAMMA;
    /* Finally record that we have an sRGB profile */
    colorspace->flags |=
       (PNG_COLORSPACE_MATCHES_sRGB|PNG_COLORSPACE_FROM_sRGB);
    return 1; /* set */
 }
 #endif /* sRGB */
 #ifdef PNG_iCCP_SUPPORTED
 /* Encoded value of D50 as an ICC XYZNumber.  From the ICC 2010 spec the value
  * is XYZ(0.9642,1.0,0.8249), which scales to:
  *
  *    (63189.8112, 65536, 54060.6464)
  */
 static const png_byte D50_nCIEXYZ[12] =
    { 0x00, 0x00, 0xf6, 0xd6, 0x00, 0x01, 0x00, 0x00, 0x00, 0x00, 0xd3, 0x2d };
 int /* PRIVATE */
 png_icc_check_length(png_const_structrp png_ptr, png_colorspacerp colorspace,
    png_const_charp name, png_uint_32 profile_length)
 {
    if (profile_length < 132)
       return png_icc_profile_error(png_ptr, colorspace, name, profile_length,
          "too short");
    if (profile_length & 3)
       return png_icc_profile_error(png_ptr, colorspace, name, profile_length,
          "invalid length");
    return 1;
 }
 int /* PRIVATE */
 png_icc_check_header(png_const_structrp png_ptr, png_colorspacerp colorspace,
    png_const_charp name, png_uint_32 profile_length,
    png_const_bytep profile/* first 132 bytes only */, int color_type)
 {
    png_uint_32 temp;
    /* Length check; this cannot be ignored in this code because profile_length
     * is used later to check the tag table, so even if the profile seems over
     * long profile_length from the caller must be correct.  The caller can fix
     * this up on read or write by just passing in the profile header length.
     */
    temp = png_get_uint_32(profile);
    if (temp != profile_length)
       return png_icc_profile_error(png_ptr, colorspace, name, temp,
          "length does not match profile");
    temp = png_get_uint_32(profile+128); /* tag count: 12 bytes/tag */
    if (temp > 357913930 || /* (2^32-4-132)/12: maximum possible tag count */
       profile_length < 132+12*temp) /* truncated tag table */
       return png_icc_profile_error(png_ptr, colorspace, name, temp,
          "tag count too large");
    /* The 'intent' must be valid or we can't store it, ICC limits the intent to
     * 16 bits.
     */
    temp = png_get_uint_32(profile+64);
    if (temp >= 0xffff) /* The ICC limit */
       return png_icc_profile_error(png_ptr, colorspace, name, temp,
          "invalid rendering intent");
    /* This is just a warning because the profile may be valid in future
     * versions.
     */
    if (temp >= PNG_sRGB_INTENT_LAST)
       (void)png_icc_profile_error(png_ptr, NULL, name, temp,
          "intent outside defined range");
    /* At this point the tag table can't be checked because it hasn't necessarily
     * been loaded; however, various header fields can be checked.  These checks
     * are for values permitted by the PNG spec in an ICC profile; the PNG spec
     * restricts the profiles that can be passed in an iCCP chunk (they must be
     * appropriate to processing PNG data!)
     */
    /* Data checks (could be skipped).  These checks must be independent of the
     * version number; however, the version number doesn't accomodate changes in
     * the header fields (just the known tags and the interpretation of the
     * data.)
     */
    temp = png_get_uint_32(profile+36); /* signature 'ascp' */
    if (temp != 0x61637370)
       return png_icc_profile_error(png_ptr, colorspace, name, temp,
          "invalid signature");
    /* Currently the PCS illuminant/adopted white point (the computational
     * white point) are required to be D50,
     * however the profile contains a record of the illuminant so perhaps ICC
     * expects to be able to change this in the future (despite the rationale in
     * the introduction for using a fixed PCS adopted white.)  Consequently the
     * following is just a warning.
     */
    if (memcmp(profile+68, D50_nCIEXYZ, 12) != 0)
       (void)png_icc_profile_error(png_ptr, NULL, name, 0/*no tag value*/,
          "PCS illuminant is not D50");
    /* The PNG spec requires this:
     * "If the iCCP chunk is present, the image samples conform to the colour
     * space represented by the embedded ICC profile as defined by the
     * International Color Consortium [ICC]. The colour space of the ICC profile
     * shall be an RGB colour space for colour images (PNG colour types 2, 3, and
     * 6), or a greyscale colour space for greyscale images (PNG colour types 0
     * and 4)."
     *
     * This checking code ensures the embedded profile (on either read or write)
     * conforms to the specification requirements.  Notice that an ICC 'gray'
     * color-space profile contains the information to transform the monochrome
     * data to XYZ or L*a*b (according to which PCS the profile uses) and this
     * should be used in preference to the standard libpng K channel replication
     * into R, G and B channels.
     *
     * Previously it was suggested that an RGB profile on grayscale data could be
     * handled.  However it it is clear that using an RGB profile in this context
     * must be an error - there is no specification of what it means.  Thus it is
     * almost certainly more correct to ignore the profile.
     */
    temp = png_get_uint_32(profile+16); /* data colour space field */
    switch (temp)
    {
       case 0x52474220: /* 'RGB ' */
          if (!(color_type & PNG_COLOR_MASK_COLOR))
             return png_icc_profile_error(png_ptr, colorspace, name, temp,
                "RGB color space not permitted on grayscale PNG");
          break;
       case 0x47524159: /* 'GRAY' */
          if (color_type & PNG_COLOR_MASK_COLOR)
             return png_icc_profile_error(png_ptr, colorspace, name, temp,
                "Gray color space not permitted on RGB PNG");
          break;
       default:
          return png_icc_profile_error(png_ptr, colorspace, name, temp,
             "invalid ICC profile color space");
    }
    /* It is up to the application to check that the profile class matches the
     * application requirements; the spec provides no guidance, but it's pretty
     * weird if the profile is not scanner ('scnr'), monitor ('mntr'), printer
     * ('prtr') or 'spac' (for generic color spaces).  Issue a warning in these
     * cases.  Issue an error for device link or abstract profiles - these don't
     * contain the records necessary to transform the color-space to anything
     * other than the target device (and not even that for an abstract profile).
     * Profiles of these classes may not be embedded in images.
     */
    temp = png_get_uint_32(profile+12); /* profile/device class */
    switch (temp)
    {
       case 0x73636E72: /* 'scnr' */
       case 0x6D6E7472: /* 'mntr' */
       case 0x70727472: /* 'prtr' */
       case 0x73706163: /* 'spac' */
          /* All supported */
          break;
       case 0x61627374: /* 'abst' */
          /* May not be embedded in an image */
          return png_icc_profile_error(png_ptr, colorspace, name, temp,
             "invalid embedded Abstract ICC profile");
       case 0x6C696E6B: /* 'link' */
          /* DeviceLink profiles cannnot be interpreted in a non-device specific
           * fashion, if an app uses the AToB0Tag in the profile the results are
           * undefined unless the result is sent to the intended device,
           * therefore a DeviceLink profile should not be found embedded in a
           * PNG.
           */
          return png_icc_profile_error(png_ptr, colorspace, name, temp,
             "unexpected DeviceLink ICC profile class");
       case 0x6E6D636C: /* 'nmcl' */
          /* A NamedColor profile is also device specific, however it doesn't
           * contain an AToB0 tag that is open to misintrepretation.  Almost
           * certainly it will fail the tests below.
           */
          (void)png_icc_profile_error(png_ptr, NULL, name, temp,
             "unexpected NamedColor ICC profile class");
          break;
       default:
          /* To allow for future enhancements to the profile accept unrecognized
           * profile classes with a warning, these then hit the test below on the
           * tag content to ensure they are backward compatible with one of the
           * understood profiles.
           */
          (void)png_icc_profile_error(png_ptr, NULL, name, temp,
             "unrecognized ICC profile class");
          break;
    }
    /* For any profile other than a device link one the PCS must be encoded
     * either in XYZ or Lab.
     */
    temp = png_get_uint_32(profile+20);
    switch (temp)
    {
       case 0x58595A20: /* 'XYZ ' */
       case 0x4C616220: /* 'Lab ' */
          break;
       default:
          return png_icc_profile_error(png_ptr, colorspace, name, temp,
             "unexpected ICC PCS encoding");
    }
    return 1;
 }
 int /* PRIVATE */
 png_icc_check_tag_table(png_const_structrp png_ptr, png_colorspacerp colorspace,
    png_const_charp name, png_uint_32 profile_length,
    png_const_bytep profile /* header plus whole tag table */)
 {
    png_uint_32 tag_count = png_get_uint_32(profile+128);
    png_uint_32 itag;
    png_const_bytep tag = profile+132; /* The first tag */
    /* First scan all the tags in the table and add bits to the icc_info value
     * (temporarily in 'tags').
     */
    for (itag=0; itag < tag_count; ++itag, tag += 12)
    {
       png_uint_32 tag_id = png_get_uint_32(tag+0);
       png_uint_32 tag_start = png_get_uint_32(tag+4); /* must be aligned */
       png_uint_32 tag_length = png_get_uint_32(tag+8);/* not padded */
       /* The ICC specification does not exclude zero length tags, therefore the
        * start might actually be anywhere if there is no data, but this would be
        * a clear abuse of the intent of the standard so the start is checked for
        * being in range.  All defined tag types have an 8 byte header - a 4 byte
        * type signature then 0.
        */
       if ((tag_start & 3) != 0)
       {
          /* CNHP730S.icc shipped with Microsoft Windows 64 violates this, it is
           * only a warning here because libpng does not care about the
           * alignment.
           */
          (void)png_icc_profile_error(png_ptr, NULL, name, tag_id,
             "ICC profile tag start not a multiple of 4");
       }
       /* This is a hard error; potentially it can cause read outside the
        * profile.
        */
       if (tag_start > profile_length || tag_length > profile_length - tag_start)
          return png_icc_profile_error(png_ptr, colorspace, name, tag_id,
             "ICC profile tag outside profile");
    }
    return 1; /* success, maybe with warnings */
 }
 #ifdef PNG_sRGB_SUPPORTED
 /* Information about the known ICC sRGB profiles */
 static const struct
 {
    png_uint_32 adler, crc, length;
    png_uint_32 md5[4];
    png_byte    have_md5;
    png_byte    is_broken;
    png_uint_16 intent;
 #  define PNG_MD5(a,b,c,d) { a, b, c, d }, (a!=0)||(b!=0)||(c!=0)||(d!=0)
 #  define PNG_ICC_CHECKSUM(adler, crc, md5, intent, broke, date, length, fname)\
       { adler, crc, length, md5, broke, intent },
 } png_sRGB_checks[] =
 {
    /* This data comes from contrib/tools/checksum-icc run on downloads of
     * all four ICC sRGB profiles from www.color.org.
     */
    /* adler32, crc32, MD5[4], intent, date, length, file-name */
    PNG_ICC_CHECKSUM(0x0a3fd9f6, 0x3b8772b9,
       PNG_MD5(0x29f83dde, 0xaff255ae, 0x7842fae4, 0xca83390d), 0, 0,
       "2009/03/27 21:36:31", 3048, "sRGB_IEC61966-2-1_black_scaled.icc")
    /* ICC sRGB v2 perceptual no black-compensation: */
    PNG_ICC_CHECKSUM(0x4909e5e1, 0x427ebb21,
       PNG_MD5(0xc95bd637, 0xe95d8a3b, 0x0df38f99, 0xc1320389), 1, 0,
       "2009/03/27 21:37:45", 3052, "sRGB_IEC61966-2-1_no_black_scaling.icc")
    PNG_ICC_CHECKSUM(0xfd2144a1, 0x306fd8ae,
       PNG_MD5(0xfc663378, 0x37e2886b, 0xfd72e983, 0x8228f1b8), 0, 0,
       "2009/08/10 17:28:01", 60988, "sRGB_v4_ICC_preference_displayclass.icc")
    /* ICC sRGB v4 perceptual */
    PNG_ICC_CHECKSUM(0x209c35d2, 0xbbef7812,
       PNG_MD5(0x34562abf, 0x994ccd06, 0x6d2c5721, 0xd0d68c5d), 0, 0,
       "2007/07/25 00:05:37", 60960, "sRGB_v4_ICC_preference.icc")
    /* The following profiles have no known MD5 checksum. If there is a match
     * on the (empty) MD5 the other fields are used to attempt a match and
     * a warning is produced.  The first two of these profiles have a 'cprt' tag
     * which suggests that they were also made by Hewlett Packard.
     */
    PNG_ICC_CHECKSUM(0xa054d762, 0x5d5129ce,
       PNG_MD5(0x00000000, 0x00000000, 0x00000000, 0x00000000), 1, 0,
       "2004/07/21 18:57:42", 3024, "sRGB_IEC61966-2-1_noBPC.icc")
    /* This is a 'mntr' (display) profile with a mediaWhitePointTag that does not
     * match the D50 PCS illuminant in the header (it is in fact the D65 values,
     * so the white point is recorded as the un-adapted value.)  The profiles
     * below only differ in one byte - the intent - and are basically the same as
     * the previous profile except for the mediaWhitePointTag error and a missing
     * chromaticAdaptationTag.
     */
    PNG_ICC_CHECKSUM(0xf784f3fb, 0x182ea552,
       PNG_MD5(0x00000000, 0x00000000, 0x00000000, 0x00000000), 0, 1/*broken*/,
       "1998/02/09 06:49:00", 3144, "HP-Microsoft sRGB v2 perceptual")
    PNG_ICC_CHECKSUM(0x0398f3fc, 0xf29e526d,
       PNG_MD5(0x00000000, 0x00000000, 0x00000000, 0x00000000), 1, 1/*broken*/,
       "1998/02/09 06:49:00", 3144, "HP-Microsoft sRGB v2 media-relative")
 };
 static int
 png_compare_ICC_profile_with_sRGB(png_const_structrp png_ptr,
    png_const_bytep profile, uLong adler)
 {
    /* The quick check is to verify just the MD5 signature and trust the
     * rest of the data.  Because the profile has already been verified for
     * correctness this is safe.  png_colorspace_set_sRGB will check the 'intent'
     * field too, so if the profile has been edited with an intent not defined
     * by sRGB (but maybe defined by a later ICC specification) the read of
     * the profile will fail at that point.
     */
    png_uint_32 length = 0;
    png_uint_32 intent = 0x10000; /* invalid */
 #if PNG_sRGB_PROFILE_CHECKS > 1
    uLong crc = 0; /* the value for 0 length data */
 #endif
    unsigned int i;
    for (i=0; i < (sizeof png_sRGB_checks) / (sizeof png_sRGB_checks[0]); ++i)
    {
       if (png_get_uint_32(profile+84) == png_sRGB_checks[i].md5[0] &&
          png_get_uint_32(profile+88) == png_sRGB_checks[i].md5[1] &&
          png_get_uint_32(profile+92) == png_sRGB_checks[i].md5[2] &&
          png_get_uint_32(profile+96) == png_sRGB_checks[i].md5[3])
       {
          /* This may be one of the old HP profiles without an MD5, in that
           * case we can only use the length and Adler32 (note that these
           * are not used by default if there is an MD5!)
           */
 #        if PNG_sRGB_PROFILE_CHECKS == 0
             if (png_sRGB_checks[i].have_md5)
                return 1+png_sRGB_checks[i].is_broken;
 #        endif
          /* Profile is unsigned or more checks have been configured in. */
          if (length == 0)
          {
             length = png_get_uint_32(profile);
             intent = png_get_uint_32(profile+64);
          }
          /* Length *and* intent must match */
          if (length == png_sRGB_checks[i].length &&
             intent == png_sRGB_checks[i].intent)
          {
             /* Now calculate the adler32 if not done already. */
             if (adler == 0)
             {
                adler = adler32(0, NULL, 0);
                adler = adler32(adler, profile, length);
             }
             if (adler == png_sRGB_checks[i].adler)
             {
                /* These basic checks suggest that the data has not been
                 * modified, but if the check level is more than 1 perform
                 * our own crc32 checksum on the data.
                 */
 #              if PNG_sRGB_PROFILE_CHECKS > 1
                   if (crc == 0)
                   {
                      crc = crc32(0, NULL, 0);
                      crc = crc32(crc, profile, length);
                   }
                   /* So this check must pass for the 'return' below to happen.
                    */
                   if (crc == png_sRGB_checks[i].crc)
 #              endif
                {
                   if (png_sRGB_checks[i].is_broken)
                   {
                      /* These profiles are known to have bad data that may cause
                       * problems if they are used, therefore attempt to
                       * discourage their use, skip the 'have_md5' warning below,
                       * which is made irrelevant by this error.
                       */
                      png_chunk_report(png_ptr, "known incorrect sRGB profile",
                         PNG_CHUNK_ERROR);
                   }
                   /* Warn that this being done; this isn't even an error since
                    * the profile is perfectly valid, but it would be nice if
                    * people used the up-to-date ones.
                    */
                   else if (!png_sRGB_checks[i].have_md5)
                   {
                      png_chunk_report(png_ptr,
                         "out-of-date sRGB profile with no signature",
                         PNG_CHUNK_WARNING);
                   }
                   return 1+png_sRGB_checks[i].is_broken;
                }
             }
          }
 # if PNG_sRGB_PROFILE_CHECKS > 0
          /* The signature matched, but the profile had been changed in some
           * way.  This probably indicates a data error or uninformed hacking.
           * Fall through to "no match".
           */
          png_chunk_report(png_ptr,
              "Not recognizing known sRGB profile that has been edited",
              PNG_CHUNK_WARNING);
          break;
 # endif
       }
    }
    return 0; /* no match */
 }
 #endif
 #ifdef PNG_sRGB_SUPPORTED
 void /* PRIVATE */
 png_icc_set_sRGB(png_const_structrp png_ptr,
    png_colorspacerp colorspace, png_const_bytep profile, uLong adler)
 {
    /* Is this profile one of the known ICC sRGB profiles?  If it is, just set
     * the sRGB information.
     */
    if (png_compare_ICC_profile_with_sRGB(png_ptr, profile, adler))
       (void)png_colorspace_set_sRGB(png_ptr, colorspace,
          (int)/*already checked*/png_get_uint_32(profile+64));
 }
 #endif /* PNG_READ_sRGB_SUPPORTED */
 int /* PRIVATE */
 png_colorspace_set_ICC(png_const_structrp png_ptr, png_colorspacerp colorspace,
    png_const_charp name, png_uint_32 profile_length, png_const_bytep profile,
    int color_type)
 {
    if (colorspace->flags & PNG_COLORSPACE_INVALID)
       return 0;
    if (png_icc_check_length(png_ptr, colorspace, name, profile_length) &&
       png_icc_check_header(png_ptr, colorspace, name, profile_length, profile,
          color_type) &&
       png_icc_check_tag_table(png_ptr, colorspace, name, profile_length,
          profile))
    {
 #     ifdef PNG_sRGB_SUPPORTED
          /* If no sRGB support, don't try storing sRGB information */
          png_icc_set_sRGB(png_ptr, colorspace, profile, 0);
 #     endif
       return 1;
    }
    /* Failure case */
    return 0;
 }
 #endif /* iCCP */
 #ifdef PNG_READ_RGB_TO_GRAY_SUPPORTED
 void /* PRIVATE */
 png_colorspace_set_rgb_coefficients(png_structrp png_ptr)
 {
    /* Set the rgb_to_gray coefficients from the colorspace. */
    if (!png_ptr->rgb_to_gray_coefficients_set &&
       (png_ptr->colorspace.flags & PNG_COLORSPACE_HAVE_ENDPOINTS) != 0)
    {
       /* png_set_background has not been called, get the coefficients from the Y
        * values of the colorspace colorants.
        */
       png_fixed_point r = png_ptr->colorspace.end_points_XYZ.red_Y;
       png_fixed_point g = png_ptr->colorspace.end_points_XYZ.green_Y;
       png_fixed_point b = png_ptr->colorspace.end_points_XYZ.blue_Y;
       png_fixed_point total = r+g+b;
       if (total > 0 &&
          r >= 0 && png_muldiv(&r, r, 32768, total) && r >= 0 && r <= 32768 &&
          g >= 0 && png_muldiv(&g, g, 32768, total) && g >= 0 && g <= 32768 &&
          b >= 0 && png_muldiv(&b, b, 32768, total) && b >= 0 && b <= 32768 &&
          r+g+b <= 32769)
       {
          /* We allow 0 coefficients here.  r+g+b may be 32769 if two or
           * all of the coefficients were rounded up.  Handle this by
           * reducing the *largest* coefficient by 1; this matches the
           * approach used for the default coefficients in pngrtran.c
           */
          int add = 0;
          if (r+g+b > 32768)
             add = -1;
          else if (r+g+b < 32768)
             add = 1;
          if (add != 0)
          {
             if (g >= r && g >= b)
                g += add;
             else if (r >= g && r >= b)
                r += add;
             else
                b += add;
          }
          /* Check for an internal error. */
          if (r+g+b != 32768)
             png_error(png_ptr,
                "internal error handling cHRM coefficients");
          else
          {
             png_ptr->rgb_to_gray_red_coeff   = (png_uint_16)r;
             png_ptr->rgb_to_gray_green_coeff = (png_uint_16)g;
          }
       }
       /* This is a png_error at present even though it could be ignored -
        * it should never happen, but it is important that if it does, the
        * bug is fixed.
        */
       else
          png_error(png_ptr, "internal error handling cHRM->XYZ");
    }
 }
 #endif
 #endif /* COLORSPACE */
 void /* PRIVATE */
 png_check_IHDR(png_const_structrp png_ptr,
    png_uint_32 width, png_uint_32 height, int bit_depth,
    int color_type, int interlace_type, int compression_type,
    int filter_type)
 {
    int error = 0;
    /* Check for width and height valid values */
    if (width == 0)
    {
       png_warning(png_ptr, "Image width is zero in IHDR");
       error = 1;
    }
    if (height == 0)
    {
       png_warning(png_ptr, "Image height is zero in IHDR");
       error = 1;
    }
 #  ifdef PNG_SET_USER_LIMITS_SUPPORTED
    if (width > png_ptr->user_width_max)
 #  else
    if (width > PNG_USER_WIDTH_MAX)
 #  endif
    {
       png_warning(png_ptr, "Image width exceeds user limit in IHDR");
       error = 1;
    }
 #  ifdef PNG_SET_USER_LIMITS_SUPPORTED
    if (height > png_ptr->user_height_max)
 #  else
    if (height > PNG_USER_HEIGHT_MAX)
 #  endif
    {
       png_warning(png_ptr, "Image height exceeds user limit in IHDR");
       error = 1;
    }
    if (width > PNG_UINT_31_MAX)
    {
       png_warning(png_ptr, "Invalid image width in IHDR");
       error = 1;
    }
    if (height > PNG_UINT_31_MAX)
    {
       png_warning(png_ptr, "Invalid image height in IHDR");
       error = 1;
    }
    /* Check other values */
    if (bit_depth != 1 && bit_depth != 2 && bit_depth != 4 &&
        bit_depth != 8 && bit_depth != 16)
    {
       png_warning(png_ptr, "Invalid bit depth in IHDR");
       error = 1;
    }
    if (color_type < 0 || color_type == 1 ||
        color_type == 5 || color_type > 6)
    {
       png_warning(png_ptr, "Invalid color type in IHDR");
       error = 1;
    }
    if (((color_type == PNG_COLOR_TYPE_PALETTE) && bit_depth > 8) ||
        ((color_type == PNG_COLOR_TYPE_RGB ||
          color_type == PNG_COLOR_TYPE_GRAY_ALPHA ||
          color_type == PNG_COLOR_TYPE_RGB_ALPHA) && bit_depth < 8))
    {
       png_warning(png_ptr, "Invalid color type/bit depth combination in IHDR");
       error = 1;
    }
    if (interlace_type >= PNG_INTERLACE_LAST)
    {
       png_warning(png_ptr, "Unknown interlace method in IHDR");
       error = 1;
    }
    if (compression_type != PNG_COMPRESSION_TYPE_BASE)
    {
       png_warning(png_ptr, "Unknown compression method in IHDR");
       error = 1;
    }
 #  ifdef PNG_MNG_FEATURES_SUPPORTED
    /* Accept filter_method 64 (intrapixel differencing) only if
     * 1. Libpng was compiled with PNG_MNG_FEATURES_SUPPORTED and
     * 2. Libpng did not read a PNG signature (this filter_method is only
     *    used in PNG datastreams that are embedded in MNG datastreams) and
     * 3. The application called png_permit_mng_features with a mask that
     *    included PNG_FLAG_MNG_FILTER_64 and
     * 4. The filter_method is 64 and
     * 5. The color_type is RGB or RGBA
     */
    if ((png_ptr->mode & PNG_HAVE_PNG_SIGNATURE) &&
        png_ptr->mng_features_permitted)
       png_warning(png_ptr, "MNG features are not allowed in a PNG datastream");
    if (filter_type != PNG_FILTER_TYPE_BASE)
    {
       if (!((png_ptr->mng_features_permitted & PNG_FLAG_MNG_FILTER_64) &&
           (filter_type == PNG_INTRAPIXEL_DIFFERENCING) &&
           ((png_ptr->mode & PNG_HAVE_PNG_SIGNATURE) == 0) &&
           (color_type == PNG_COLOR_TYPE_RGB ||
           color_type == PNG_COLOR_TYPE_RGB_ALPHA)))
       {
          png_warning(png_ptr, "Unknown filter method in IHDR");
          error = 1;
       }
       if (png_ptr->mode & PNG_HAVE_PNG_SIGNATURE)
       {
          png_warning(png_ptr, "Invalid filter method in IHDR");
          error = 1;
       }
    }
 #  else
    if (filter_type != PNG_FILTER_TYPE_BASE)
    {
       png_warning(png_ptr, "Unknown filter method in IHDR");
       error = 1;
    }
 #  endif
    if (error == 1)
       png_error(png_ptr, "Invalid IHDR data");
 }
 #if defined(PNG_sCAL_SUPPORTED) || defined(PNG_pCAL_SUPPORTED)
 /* ASCII to fp functions */
 /* Check an ASCII formated floating point value, see the more detailed
  * comments in pngpriv.h
  */
 /* The following is used internally to preserve the sticky flags */
 #define png_fp_add(state, flags) ((state) |= (flags))
 #define png_fp_set(state, value) ((state) = (value) | ((state) & PNG_FP_STICKY))
 int /* PRIVATE */
 png_check_fp_number(png_const_charp string, png_size_t size, int *statep,
    png_size_tp whereami)
 {
    int state = *statep;
    png_size_t i = *whereami;
    while (i < size)
    {
       int type;
       /* First find the type of the next character */
       switch (string[i])
       {
       case 43:  type = PNG_FP_SAW_SIGN;                   break;
       case 45:  type = PNG_FP_SAW_SIGN + PNG_FP_NEGATIVE; break;
       case 46:  type = PNG_FP_SAW_DOT;                    break;
       case 48:  type = PNG_FP_SAW_DIGIT;                  break;
       case 49: case 50: case 51: case 52:
       case 53: case 54: case 55: case 56:
       case 57:  type = PNG_FP_SAW_DIGIT + PNG_FP_NONZERO; break;
       case 69:
       case 101: type = PNG_FP_SAW_E;                      break;
       default:  goto PNG_FP_End;
       }
       /* Now deal with this type according to the current
        * state, the type is arranged to not overlap the
        * bits of the PNG_FP_STATE.
        */
       switch ((state & PNG_FP_STATE) + (type & PNG_FP_SAW_ANY))
       {
       case PNG_FP_INTEGER + PNG_FP_SAW_SIGN:
          if (state & PNG_FP_SAW_ANY)
             goto PNG_FP_End; /* not a part of the number */
          png_fp_add(state, type);
          break;
       case PNG_FP_INTEGER + PNG_FP_SAW_DOT:
          /* Ok as trailer, ok as lead of fraction. */
          if (state & PNG_FP_SAW_DOT) /* two dots */
             goto PNG_FP_End;
          else if (state & PNG_FP_SAW_DIGIT) /* trailing dot? */
             png_fp_add(state, type);
          else
             png_fp_set(state, PNG_FP_FRACTION | type);
          break;
       case PNG_FP_INTEGER + PNG_FP_SAW_DIGIT:
          if (state & PNG_FP_SAW_DOT) /* delayed fraction */
             png_fp_set(state, PNG_FP_FRACTION | PNG_FP_SAW_DOT);
          png_fp_add(state, type | PNG_FP_WAS_VALID);
          break;
       case PNG_FP_INTEGER + PNG_FP_SAW_E:
          if ((state & PNG_FP_SAW_DIGIT) == 0)
             goto PNG_FP_End;
          png_fp_set(state, PNG_FP_EXPONENT);
          break;
    /* case PNG_FP_FRACTION + PNG_FP_SAW_SIGN:
          goto PNG_FP_End; ** no sign in fraction */
    /* case PNG_FP_FRACTION + PNG_FP_SAW_DOT:
          goto PNG_FP_End; ** Because SAW_DOT is always set */
       case PNG_FP_FRACTION + PNG_FP_SAW_DIGIT:
          png_fp_add(state, type | PNG_FP_WAS_VALID);
          break;
       case PNG_FP_FRACTION + PNG_FP_SAW_E:
          /* This is correct because the trailing '.' on an
           * integer is handled above - so we can only get here
           * with the sequence ".E" (with no preceding digits).
           */
          if ((state & PNG_FP_SAW_DIGIT) == 0)
             goto PNG_FP_End;
          png_fp_set(state, PNG_FP_EXPONENT);
          break;
       case PNG_FP_EXPONENT + PNG_FP_SAW_SIGN:
          if (state & PNG_FP_SAW_ANY)
             goto PNG_FP_End; /* not a part of the number */
          png_fp_add(state, PNG_FP_SAW_SIGN);
          break;
    /* case PNG_FP_EXPONENT + PNG_FP_SAW_DOT:
          goto PNG_FP_End; */
       case PNG_FP_EXPONENT + PNG_FP_SAW_DIGIT:
          png_fp_add(state, PNG_FP_SAW_DIGIT | PNG_FP_WAS_VALID);
          break;
    /* case PNG_FP_EXPONEXT + PNG_FP_SAW_E:
          goto PNG_FP_End; */
       default: goto PNG_FP_End; /* I.e. break 2 */
       }
       /* The character seems ok, continue. */
       ++i;
    }
 PNG_FP_End:
    /* Here at the end, update the state and return the correct
     * return code.
     */
    *statep = state;
    *whereami = i;
    return (state & PNG_FP_SAW_DIGIT) != 0;
 }
 /* The same but for a complete string. */
 int
 png_check_fp_string(png_const_charp string, png_size_t size)
 {
    int        state=0;
    png_size_t char_index=0;
    if (png_check_fp_number(string, size, &state, &char_index) &&
       (char_index == size || string[char_index] == 0))
       return state /* must be non-zero - see above */;
    return 0; /* i.e. fail */
 }
 #endif /* pCAL or sCAL */
 #ifdef PNG_sCAL_SUPPORTED
 #  ifdef PNG_FLOATING_POINT_SUPPORTED
 /* Utility used below - a simple accurate power of ten from an integral
  * exponent.
  */
 static double
 png_pow10(int power)
 {
    int recip = 0;
    double d = 1;
    /* Handle negative exponent with a reciprocal at the end because
     * 10 is exact whereas .1 is inexact in base 2
     */
    if (power < 0)
    {
       if (power < DBL_MIN_10_EXP) return 0;
       recip = 1, power = -power;
    }
    if (power > 0)
    {
       /* Decompose power bitwise. */
       double mult = 10;
       do
       {
          if (power & 1) d *= mult;
          mult *= mult;
          power >>= 1;
       }
       while (power > 0);
       if (recip) d = 1/d;
    }
    /* else power is 0 and d is 1 */
    return d;
 }
 /* Function to format a floating point value in ASCII with a given
  * precision.
  */
 void /* PRIVATE */
 png_ascii_from_fp(png_const_structrp png_ptr, png_charp ascii, png_size_t size,
     double fp, unsigned int precision)
 {
    /* We use standard functions from math.h, but not printf because
     * that would require stdio.  The caller must supply a buffer of
     * sufficient size or we will png_error.  The tests on size and
     * the space in ascii[] consumed are indicated below.
     */
    if (precision < 1)
       precision = DBL_DIG;
    /* Enforce the limit of the implementation precision too. */
    if (precision > DBL_DIG+1)
       precision = DBL_DIG+1;
    /* Basic sanity checks */
    if (size >= precision+5) /* See the requirements below. */
    {
       if (fp < 0)
       {
          fp = -fp;
          *ascii++ = 45; /* '-'  PLUS 1 TOTAL 1 */
          --size;
       }
       if (fp >= DBL_MIN && fp <= DBL_MAX)
       {
          int exp_b10;       /* A base 10 exponent */
          double base;   /* 10^exp_b10 */
          /* First extract a base 10 exponent of the number,
           * the calculation below rounds down when converting
           * from base 2 to base 10 (multiply by log10(2) -
           * 0.3010, but 77/256 is 0.3008, so exp_b10 needs to
           * be increased.  Note that the arithmetic shift
           * performs a floor() unlike C arithmetic - using a
           * C multiply would break the following for negative
           * exponents.
           */
          (void)frexp(fp, &exp_b10); /* exponent to base 2 */
          exp_b10 = (exp_b10 * 77) >> 8; /* <= exponent to base 10 */
          /* Avoid underflow here. */
          base = png_pow10(exp_b10); /* May underflow */
          while (base < DBL_MIN || base < fp)
          {
             /* And this may overflow. */
             double test = png_pow10(exp_b10+1);
             if (test <= DBL_MAX)
                ++exp_b10, base = test;
             else
                break;
          }
          /* Normalize fp and correct exp_b10, after this fp is in the
           * range [.1,1) and exp_b10 is both the exponent and the digit
           * *before* which the decimal point should be inserted
           * (starting with 0 for the first digit).  Note that this
           * works even if 10^exp_b10 is out of range because of the
           * test on DBL_MAX above.
           */
          fp /= base;
          while (fp >= 1) fp /= 10, ++exp_b10;
          /* Because of the code above fp may, at this point, be
           * less than .1, this is ok because the code below can
           * handle the leading zeros this generates, so no attempt
           * is made to correct that here.
           */
          {
             int czero, clead, cdigits;
             char exponent[10];
             /* Allow up to two leading zeros - this will not lengthen
              * the number compared to using E-n.
              */
             if (exp_b10 < 0 && exp_b10 > -3) /* PLUS 3 TOTAL 4 */
             {
                czero = -exp_b10; /* PLUS 2 digits: TOTAL 3 */
                exp_b10 = 0;      /* Dot added below before first output. */
             }
             else
                czero = 0;    /* No zeros to add */
             /* Generate the digit list, stripping trailing zeros and
              * inserting a '.' before a digit if the exponent is 0.
              */
             clead = czero; /* Count of leading zeros */
             cdigits = 0;   /* Count of digits in list. */
             do
             {
                double d;
                fp *= 10;
                /* Use modf here, not floor and subtract, so that
                 * the separation is done in one step.  At the end
                 * of the loop don't break the number into parts so
                 * that the final digit is rounded.
                 */
                if (cdigits+czero-clead+1 < (int)precision)
                   fp = modf(fp, &d);
                else
                {
                   d = floor(fp + .5);
                   if (d > 9)
                   {
                      /* Rounding up to 10, handle that here. */
                      if (czero > 0)
                      {
                         --czero, d = 1;
                         if (cdigits == 0) --clead;
                      }
                      else
                      {
                         while (cdigits > 0 && d > 9)
                         {
                            int ch = *--ascii;
                            if (exp_b10 != (-1))
                               ++exp_b10;
                            else if (ch == 46)
                            {
                               ch = *--ascii, ++size;
                               /* Advance exp_b10 to '1', so that the
                                * decimal point happens after the
                                * previous digit.
                                */
                               exp_b10 = 1;
                            }
                            --cdigits;
                            d = ch - 47;  /* I.e. 1+(ch-48) */
                         }
                         /* Did we reach the beginning? If so adjust the
                          * exponent but take into account the leading
                          * decimal point.
                          */
                         if (d > 9)  /* cdigits == 0 */
                         {
                            if (exp_b10 == (-1))
                            {
                               /* Leading decimal point (plus zeros?), if
                                * we lose the decimal point here it must
                                * be reentered below.
                                */
                               int ch = *--ascii;
                               if (ch == 46)
                                  ++size, exp_b10 = 1;
                               /* Else lost a leading zero, so 'exp_b10' is
                                * still ok at (-1)
                                */
                            }
                            else
                               ++exp_b10;
                            /* In all cases we output a '1' */
                            d = 1;
                         }
                      }
                   }
                   fp = 0; /* Guarantees termination below. */
                }
                if (d == 0)
                {
                   ++czero;
                   if (cdigits == 0) ++clead;
                }
                else
                {
                   /* Included embedded zeros in the digit count. */
                   cdigits += czero - clead;
                   clead = 0;
                   while (czero > 0)
                   {
                      /* exp_b10 == (-1) means we just output the decimal
                       * place - after the DP don't adjust 'exp_b10' any
                       * more!
                       */
                      if (exp_b10 != (-1))
                      {
                         if (exp_b10 == 0) *ascii++ = 46, --size;
                         /* PLUS 1: TOTAL 4 */
                         --exp_b10;
                      }
                      *ascii++ = 48, --czero;
                   }
                   if (exp_b10 != (-1))
                   {
                      if (exp_b10 == 0) *ascii++ = 46, --size; /* counted
                                                                  above */
                      --exp_b10;
                   }
                   *ascii++ = (char)(48 + (int)d), ++cdigits;
                }
             }
             while (cdigits+czero-clead < (int)precision && fp > DBL_MIN);
             /* The total output count (max) is now 4+precision */
             /* Check for an exponent, if we don't need one we are
              * done and just need to terminate the string.  At
              * this point exp_b10==(-1) is effectively if flag - it got
              * to '-1' because of the decrement after outputing
              * the decimal point above (the exponent required is
              * *not* -1!)
              */
             if (exp_b10 >= (-1) && exp_b10 <= 2)
             {
                /* The following only happens if we didn't output the
                 * leading zeros above for negative exponent, so this
                 * doest add to the digit requirement.  Note that the
                 * two zeros here can only be output if the two leading
                 * zeros were *not* output, so this doesn't increase
                 * the output count.
                 */
                while (--exp_b10 >= 0) *ascii++ = 48;
                *ascii = 0;
                /* Total buffer requirement (including the '\0') is
                 * 5+precision - see check at the start.
                 */
                return;
             }
             /* Here if an exponent is required, adjust size for
              * the digits we output but did not count.  The total
              * digit output here so far is at most 1+precision - no
              * decimal point and no leading or trailing zeros have
              * been output.
              */
             size -= cdigits;
             *ascii++ = 69, --size;    /* 'E': PLUS 1 TOTAL 2+precision */
             /* The following use of an unsigned temporary avoids ambiguities in
              * the signed arithmetic on exp_b10 and permits GCC at least to do
              * better optimization.
              */
             {
                unsigned int uexp_b10;
                if (exp_b10 < 0)
                {
                   *ascii++ = 45, --size; /* '-': PLUS 1 TOTAL 3+precision */
                   uexp_b10 = -exp_b10;
                }
                else
                   uexp_b10 = exp_b10;
                cdigits = 0;
                while (uexp_b10 > 0)
                {
                   exponent[cdigits++] = (char)(48 + uexp_b10 % 10);
                   uexp_b10 /= 10;
                }
             }
             /* Need another size check here for the exponent digits, so
              * this need not be considered above.
              */
             if ((int)size > cdigits)
             {
                while (cdigits > 0) *ascii++ = exponent[--cdigits];
                *ascii = 0;
                return;
             }
          }
       }
       else if (!(fp >= DBL_MIN))
       {
          *ascii++ = 48; /* '0' */
          *ascii = 0;
          return;
       }
       else
       {
          *ascii++ = 105; /* 'i' */
          *ascii++ = 110; /* 'n' */
          *ascii++ = 102; /* 'f' */
          *ascii = 0;
          return;
       }
    }
    /* Here on buffer too small. */
    png_error(png_ptr, "ASCII conversion buffer too small");
 }
 #  endif /* FLOATING_POINT */
 #  ifdef PNG_FIXED_POINT_SUPPORTED
 /* Function to format a fixed point value in ASCII.
  */
 void /* PRIVATE */
 png_ascii_from_fixed(png_const_structrp png_ptr, png_charp ascii,
     png_size_t size, png_fixed_point fp)
 {
    /* Require space for 10 decimal digits, a decimal point, a minus sign and a
     * trailing \0, 13 characters:
     */
    if (size > 12)
    {
       png_uint_32 num;
       /* Avoid overflow here on the minimum integer. */
       if (fp < 0)
          *ascii++ = 45, --size, num = -fp;
       else
          num = fp;
       if (num <= 0x80000000) /* else overflowed */
       {
          unsigned int ndigits = 0, first = 16 /* flag value */;
          char digits[10];
          while (num)
          {
             /* Split the low digit off num: */
             unsigned int tmp = num/10;
             num -= tmp*10;
             digits[ndigits++] = (char)(48 + num);
             /* Record the first non-zero digit, note that this is a number
              * starting at 1, it's not actually the array index.
              */
             if (first == 16 && num > 0)
                first = ndigits;
             num = tmp;
          }
          if (ndigits > 0)
          {
             while (ndigits > 5) *ascii++ = digits[--ndigits];
             /* The remaining digits are fractional digits, ndigits is '5' or
              * smaller at this point.  It is certainly not zero.  Check for a
              * non-zero fractional digit:
              */
             if (first <= 5)
             {
                unsigned int i;
                *ascii++ = 46; /* decimal point */
                /* ndigits may be <5 for small numbers, output leading zeros
                 * then ndigits digits to first:
                 */
                i = 5;
                while (ndigits < i) *ascii++ = 48, --i;
                while (ndigits >= first) *ascii++ = digits[--ndigits];
                /* Don't output the trailing zeros! */
             }
          }
          else
             *ascii++ = 48;
          /* And null terminate the string: */
          *ascii = 0;
          return;
       }
    }
    /* Here on buffer too small. */
    png_error(png_ptr, "ASCII conversion buffer too small");
 }
 #   endif /* FIXED_POINT */
 #endif /* READ_SCAL */
 #if defined(PNG_FLOATING_POINT_SUPPORTED) && \
    !defined(PNG_FIXED_POINT_MACRO_SUPPORTED) && \
    (defined(PNG_gAMA_SUPPORTED) || defined(PNG_cHRM_SUPPORTED) || \
    defined(PNG_sCAL_SUPPORTED) || defined(PNG_READ_BACKGROUND_SUPPORTED) || \
    defined(PNG_READ_RGB_TO_GRAY_SUPPORTED)) || \
    (defined(PNG_sCAL_SUPPORTED) && \
    defined(PNG_FLOATING_ARITHMETIC_SUPPORTED))
 png_fixed_point
 png_fixed(png_const_structrp png_ptr, double fp, png_const_charp text)
 {
    double r = floor(100000 * fp + .5);
    if (r > 2147483647. || r < -2147483648.)
       png_fixed_error(png_ptr, text);
 #  ifndef PNG_ERROR_TEXT_SUPPORTED
       PNG_UNUSED(text)
 #  endif
    return (png_fixed_point)r;
 }
 #endif
 #if defined(PNG_GAMMA_SUPPORTED) || defined(PNG_COLORSPACE_SUPPORTED) ||\
     defined(PNG_INCH_CONVERSIONS_SUPPORTED) || defined(PNG_READ_pHYs_SUPPORTED)
 /* muldiv functions */
 /* This API takes signed arguments and rounds the result to the nearest
  * integer (or, for a fixed point number - the standard argument - to
  * the nearest .00001).  Overflow and divide by zero are signalled in
  * the result, a boolean - true on success, false on overflow.
  */
 int
 png_muldiv(png_fixed_point_p res, png_fixed_point a, png_int_32 times,
     png_int_32 divisor)
 {
    /* Return a * times / divisor, rounded. */
    if (divisor != 0)
    {
       if (a == 0 || times == 0)
       {
          *res = 0;
          return 1;
       }
       else
       {
 #ifdef PNG_FLOATING_ARITHMETIC_SUPPORTED
          double r = a;
          r *= times;
          r /= divisor;
          r = floor(r+.5);
          /* A png_fixed_point is a 32-bit integer. */
          if (r <= 2147483647. && r >= -2147483648.)
          {
             *res = (png_fixed_point)r;
             return 1;
          }
 #else
          int negative = 0;
          png_uint_32 A, T, D;
          png_uint_32 s16, s32, s00;
          if (a < 0)
             negative = 1, A = -a;
          else
             A = a;
          if (times < 0)
             negative = !negative, T = -times;
          else
             T = times;
          if (divisor < 0)
             negative = !negative, D = -divisor;
          else
             D = divisor;
          /* Following can't overflow because the arguments only
           * have 31 bits each, however the result may be 32 bits.
           */
          s16 = (A >> 16) * (T & 0xffff) +
                            (A & 0xffff) * (T >> 16);
          /* Can't overflow because the a*times bit is only 30
           * bits at most.
           */
          s32 = (A >> 16) * (T >> 16) + (s16 >> 16);
          s00 = (A & 0xffff) * (T & 0xffff);
          s16 = (s16 & 0xffff) << 16;
          s00 += s16;
          if (s00 < s16)
             ++s32; /* carry */
          if (s32 < D) /* else overflow */
          {
             /* s32.s00 is now the 64-bit product, do a standard
              * division, we know that s32 < D, so the maximum
              * required shift is 31.
              */
             int bitshift = 32;
             png_fixed_point result = 0; /* NOTE: signed */
             while (--bitshift >= 0)
             {
                png_uint_32 d32, d00;
                if (bitshift > 0)
                   d32 = D >> (32-bitshift), d00 = D << bitshift;
                else
                   d32 = 0, d00 = D;
                if (s32 > d32)
                {
                   if (s00 < d00) --s32; /* carry */
                   s32 -= d32, s00 -= d00, result += 1<<bitshift;
                }
                else
                   if (s32 == d32 && s00 >= d00)
                      s32 = 0, s00 -= d00, result += 1<<bitshift;
             }
             /* Handle the rounding. */
             if (s00 >= (D >> 1))
                ++result;
             if (negative)
                result = -result;
             /* Check for overflow. */
             if ((negative && result <= 0) || (!negative && result >= 0))
             {
                *res = result;
                return 1;
             }
          }
 #endif
       }
    }
    return 0;
 }
 #endif /* READ_GAMMA || INCH_CONVERSIONS */
 #if defined(PNG_READ_GAMMA_SUPPORTED) || defined(PNG_INCH_CONVERSIONS_SUPPORTED)
 /* The following is for when the caller doesn't much care about the
  * result.
  */
 png_fixed_point
 png_muldiv_warn(png_const_structrp png_ptr, png_fixed_point a, png_int_32 times,
     png_int_32 divisor)
 {
    png_fixed_point result;
    if (png_muldiv(&result, a, times, divisor))
       return result;
    png_warning(png_ptr, "fixed point overflow ignored");
    return 0;
 }
 #endif
 #ifdef PNG_GAMMA_SUPPORTED /* more fixed point functions for gamma */
 /* Calculate a reciprocal, return 0 on div-by-zero or overflow. */
 png_fixed_point
 png_reciprocal(png_fixed_point a)
 {
 #ifdef PNG_FLOATING_ARITHMETIC_SUPPORTED
    double r = floor(1E10/a+.5);
    if (r <= 2147483647. && r >= -2147483648.)
       return (png_fixed_point)r;
 #else
    png_fixed_point res;
    if (png_muldiv(&res, 100000, 100000, a))
       return res;
 #endif
    return 0; /* error/overflow */
 }
 /* This is the shared test on whether a gamma value is 'significant' - whether
  * it is worth doing gamma correction.
  */
 int /* PRIVATE */
 png_gamma_significant(png_fixed_point gamma_val)
 {
    return gamma_val < PNG_FP_1 - PNG_GAMMA_THRESHOLD_FIXED ||
        gamma_val > PNG_FP_1 + PNG_GAMMA_THRESHOLD_FIXED;
 }
 #endif
 #ifdef PNG_READ_GAMMA_SUPPORTED
 #  ifdef PNG_16BIT_SUPPORTED
 /* A local convenience routine. */
 static png_fixed_point
 png_product2(png_fixed_point a, png_fixed_point b)
 {
    /* The required result is 1/a * 1/b; the following preserves accuracy. */
 #    ifdef PNG_FLOATING_ARITHMETIC_SUPPORTED
    double r = a * 1E-5;
    r *= b;
    r = floor(r+.5);
    if (r <= 2147483647. && r >= -2147483648.)
       return (png_fixed_point)r;
 #    else
    png_fixed_point res;
    if (png_muldiv(&res, a, b, 100000))
       return res;
 #    endif
    return 0; /* overflow */
 }
 #  endif /* 16BIT */
 /* The inverse of the above. */
 png_fixed_point
 png_reciprocal2(png_fixed_point a, png_fixed_point b)
 {
    /* The required result is 1/a * 1/b; the following preserves accuracy. */
 #ifdef PNG_FLOATING_ARITHMETIC_SUPPORTED
    double r = 1E15/a;
    r /= b;
    r = floor(r+.5);
    if (r <= 2147483647. && r >= -2147483648.)
       return (png_fixed_point)r;
 #else
    /* This may overflow because the range of png_fixed_point isn't symmetric,
     * but this API is only used for the product of file and screen gamma so it
     * doesn't matter that the smallest number it can produce is 1/21474, not
     * 1/100000
     */
    png_fixed_point res = png_product2(a, b);
    if (res != 0)
       return png_reciprocal(res);
 #endif
    return 0; /* overflow */
 }
 #endif /* READ_GAMMA */
 #ifdef PNG_READ_GAMMA_SUPPORTED /* gamma table code */
 #ifndef PNG_FLOATING_ARITHMETIC_SUPPORTED
 /* Fixed point gamma.
  *
  * The code to calculate the tables used below can be found in the shell script
  * contrib/tools/intgamma.sh
  *
  * To calculate gamma this code implements fast log() and exp() calls using only
  * fixed point arithmetic.  This code has sufficient precision for either 8-bit
  * or 16-bit sample values.
  *
  * The tables used here were calculated using simple 'bc' programs, but C double
  * precision floating point arithmetic would work fine.
  *
  * 8-bit log table
  *   This is a table of -log(value/255)/log(2) for 'value' in the range 128 to
  *   255, so it's the base 2 logarithm of a normalized 8-bit floating point
  *   mantissa.  The numbers are 32-bit fractions.
  */
 static const png_uint_32
 png_8bit_l2[128] =
 {
    4270715492U, 4222494797U, 4174646467U, 4127164793U, 4080044201U, 4033279239U,
    3986864580U, 3940795015U, 3895065449U, 3849670902U, 3804606499U, 3759867474U,
    3715449162U, 3671346997U, 3627556511U, 3584073329U, 3540893168U, 3498011834U,
    3455425220U, 3413129301U, 3371120137U, 3329393864U, 3287946700U, 3246774933U,
    3205874930U, 3165243125U, 3124876025U, 3084770202U, 3044922296U, 3005329011U,
    2965987113U, 2926893432U, 2888044853U, 2849438323U, 2811070844U, 2772939474U,
    2735041326U, 2697373562U, 2659933400U, 2622718104U, 2585724991U, 2548951424U,
    2512394810U, 2476052606U, 2439922311U, 2404001468U, 2368287663U, 2332778523U,
    2297471715U, 2262364947U, 2227455964U, 2192742551U, 2158222529U, 2123893754U,
    2089754119U, 2055801552U, 2022034013U, 1988449497U, 1955046031U, 1921821672U,
    1888774511U, 1855902668U, 1823204291U, 1790677560U, 1758320682U, 1726131893U,
    1694109454U, 1662251657U, 1630556815U, 1599023271U, 1567649391U, 1536433567U,
    1505374214U, 1474469770U, 1443718700U, 1413119487U, 1382670639U, 1352370686U,
    1322218179U, 1292211689U, 1262349810U, 1232631153U, 1203054352U, 1173618059U,
    1144320946U, 1115161701U, 1086139034U, 1057251672U, 1028498358U, 999877854U,
    971388940U, 943030410U, 914801076U, 886699767U, 858725327U, 830876614U,
    803152505U, 775551890U, 748073672U, 720716771U, 693480120U, 666362667U,
    639363374U, 612481215U, 585715177U, 559064263U, 532527486U, 506103872U,
    479792461U, 453592303U, 427502463U, 401522014U, 375650043U, 349885648U,
    324227938U, 298676034U, 273229066U, 247886176U, 222646516U, 197509248U,
    172473545U, 147538590U, 122703574U, 97967701U, 73330182U, 48790236U,
    24347096U, 0U
 #if 0
    /* The following are the values for 16-bit tables - these work fine for the
     * 8-bit conversions but produce very slightly larger errors in the 16-bit
     * log (about 1.2 as opposed to 0.7 absolute error in the final value).  To
     * use these all the shifts below must be adjusted appropriately.
     */
 , 64430, 63700, 62976, 62257, 61543, 60835, 60132, 59434, 58741, 58054,
 , 56693, 56020, 55352, 54689, 54030, 53375, 52726, 52080, 51439, 50803,
 , 49542, 48918, 48298, 47682, 47070, 46462, 45858, 45257, 44661, 44068,
 , 42894, 42312, 41733, 41159, 40587, 40020, 39455, 38894, 38336, 37782,
 , 36682, 36137, 35595, 35057, 34521, 33988, 33459, 32932, 32408, 31887,
 , 30854, 30341, 29832, 29325, 28820, 28319, 27820, 27324, 26830, 26339,
 , 25364, 24880, 24399, 23920, 23444, 22970, 22499, 22029, 21562, 21098,
 , 20175, 19718, 19262, 18808, 18357, 17908, 17461, 17016, 16573, 16132,
 , 15257, 14822, 14390, 13959, 13530, 13103, 12678, 12255, 11834, 11415,
 , 10582, 10168, 9756, 9346, 8937, 8531, 8126, 7723, 7321, 6921, 6523,
 , 5732, 5339, 4947, 4557, 4169, 3782, 3397, 3014, 2632, 2251, 1872, 1495,
 , 744, 372
 #endif
 };
 static png_int_32
 png_log8bit(unsigned int x)
 {
    unsigned int lg2 = 0;
    /* Each time 'x' is multiplied by 2, 1 must be subtracted off the final log,
     * because the log is actually negate that means adding 1.  The final
     * returned value thus has the range 0 (for 255 input) to 7.994 (for 1
     * input), return -1 for the overflow (log 0) case, - so the result is
     * always at most 19 bits.
     */
    if ((x &= 0xff) == 0)
       return -1;
    if ((x & 0xf0) == 0)
       lg2  = 4, x <<= 4;
    if ((x & 0xc0) == 0)
       lg2 += 2, x <<= 2;
    if ((x & 0x80) == 0)
       lg2 += 1, x <<= 1;
    /* result is at most 19 bits, so this cast is safe: */
    return (png_int_32)((lg2 << 16) + ((png_8bit_l2[x-128]+32768)>>16));
 }
 /* The above gives exact (to 16 binary places) log2 values for 8-bit images,
  * for 16-bit images we use the most significant 8 bits of the 16-bit value to
  * get an approximation then multiply the approximation by a correction factor
  * determined by the remaining up to 8 bits.  This requires an additional step
  * in the 16-bit case.
  *
  * We want log2(value/65535), we have log2(v'/255), where:
  *
  *    value = v' * 256 + v''
  *          = v' * f
  *
  * So f is value/v', which is equal to (256+v''/v') since v' is in the range 128
  * to 255 and v'' is in the range 0 to 255 f will be in the range 256 to less
  * than 258.  The final factor also needs to correct for the fact that our 8-bit
  * value is scaled by 255, whereas the 16-bit values must be scaled by 65535.
  *
  * This gives a final formula using a calculated value 'x' which is value/v' and
  * scaling by 65536 to match the above table:
  *
  *   log2(x/257) * 65536
  *
  * Since these numbers are so close to '1' we can use simple linear
  * interpolation between the two end values 256/257 (result -368.61) and 258/257
  * (result 367.179).  The values used below are scaled by a further 64 to give
  * 16-bit precision in the interpolation:
  *
  * Start (256): -23591
  * Zero  (257):      0
  * End   (258):  23499
  */
 static png_int_32
 png_log16bit(png_uint_32 x)
 {
    unsigned int lg2 = 0;
    /* As above, but now the input has 16 bits. */
    if ((x &= 0xffff) == 0)
       return -1;
    if ((x & 0xff00) == 0)
       lg2  = 8, x <<= 8;
    if ((x & 0xf000) == 0)
       lg2 += 4, x <<= 4;
    if ((x & 0xc000) == 0)
       lg2 += 2, x <<= 2;
    if ((x & 0x8000) == 0)
       lg2 += 1, x <<= 1;
    /* Calculate the base logarithm from the top 8 bits as a 28-bit fractional
     * value.
     */
    lg2 <<= 28;
    lg2 += (png_8bit_l2[(x>>8)-128]+8) >> 4;
    /* Now we need to interpolate the factor, this requires a division by the top
     * 8 bits.  Do this with maximum precision.
     */
    x = ((x << 16) + (x >> 9)) / (x >> 8);
    /* Since we divided by the top 8 bits of 'x' there will be a '1' at 1<<24,
     * the value at 1<<16 (ignoring this) will be 0 or 1; this gives us exactly
     * 16 bits to interpolate to get the low bits of the result.  Round the
     * answer.  Note that the end point values are scaled by 64 to retain overall
     * precision and that 'lg2' is current scaled by an extra 12 bits, so adjust
     * the overall scaling by 6-12.  Round at every step.
     */
    x -= 1U << 24;
    if (x <= 65536U) /* <= '257' */
       lg2 += ((23591U * (65536U-x)) + (1U << (16+6-12-1))) >> (16+6-12);
    else
       lg2 -= ((23499U * (x-65536U)) + (1U << (16+6-12-1))) >> (16+6-12);
    /* Safe, because the result can't have more than 20 bits: */
    return (png_int_32)((lg2 + 2048) >> 12);
 }
 /* The 'exp()' case must invert the above, taking a 20-bit fixed point
  * logarithmic value and returning a 16 or 8-bit number as appropriate.  In
  * each case only the low 16 bits are relevant - the fraction - since the
  * integer bits (the top 4) simply determine a shift.
  *
  * The worst case is the 16-bit distinction between 65535 and 65534, this
  * requires perhaps spurious accuracty in the decoding of the logarithm to
  * distinguish log2(65535/65534.5) - 10^-5 or 17 bits.  There is little chance
  * of getting this accuracy in practice.
  *
  * To deal with this the following exp() function works out the exponent of the
  * frational part of the logarithm by using an accurate 32-bit value from the
  * top four fractional bits then multiplying in the remaining bits.
  */
 static const png_uint_32
 png_32bit_exp[16] =
 {
    /* NOTE: the first entry is deliberately set to the maximum 32-bit value. */
    4294967295U, 4112874773U, 3938502376U, 3771522796U, 3611622603U, 3458501653U,
    3311872529U, 3171459999U, 3037000500U, 2908241642U, 2784941738U, 2666869345U,
    2553802834U, 2445529972U, 2341847524U, 2242560872U
 };
 /* Adjustment table; provided to explain the numbers in the code below. */
 #if 0
 for (i=11;i>=0;--i){ print i, " ", (1 - e(-(2^i)/65536*l(2))) * 2^(32-i), "\n"}
 44937.64284865548751208448
 45180.98734845585101160448
 45303.31936980687359311872
 45364.65110595323018870784
 45395.35850361789624614912
 45410.72259715102037508096
 45418.40724413220722311168
 45422.25021786898173001728
 45424.17186732298419044352
 45425.13273269940811464704
 45425.61317555035558641664
 45425.85339951654943850496
 #endif
 static png_uint_32
 png_exp(png_fixed_point x)
 {
    if (x > 0 && x <= 0xfffff) /* Else overflow or zero (underflow) */
    {
       /* Obtain a 4-bit approximation */
       png_uint_32 e = png_32bit_exp[(x >> 12) & 0xf];
       /* Incorporate the low 12 bits - these decrease the returned value by
        * multiplying by a number less than 1 if the bit is set.  The multiplier
        * is determined by the above table and the shift. Notice that the values
        * converge on 45426 and this is used to allow linear interpolation of the
        * low bits.
        */
       if (x & 0x800)
          e -= (((e >> 16) * 44938U) +  16U) >> 5;
       if (x & 0x400)
          e -= (((e >> 16) * 45181U) +  32U) >> 6;
       if (x & 0x200)
          e -= (((e >> 16) * 45303U) +  64U) >> 7;
       if (x & 0x100)
          e -= (((e >> 16) * 45365U) + 128U) >> 8;
       if (x & 0x080)
          e -= (((e >> 16) * 45395U) + 256U) >> 9;
       if (x & 0x040)
          e -= (((e >> 16) * 45410U) + 512U) >> 10;
       /* And handle the low 6 bits in a single block. */
       e -= (((e >> 16) * 355U * (x & 0x3fU)) + 256U) >> 9;
       /* Handle the upper bits of x. */
       e >>= x >> 16;
       return e;
    }
    /* Check for overflow */
    if (x <= 0)
       return png_32bit_exp[0];
    /* Else underflow */
    return 0;
 }
 static png_byte
 png_exp8bit(png_fixed_point lg2)
 {
    /* Get a 32-bit value: */
    png_uint_32 x = png_exp(lg2);
    /* Convert the 32-bit value to 0..255 by multiplying by 256-1, note that the
     * second, rounding, step can't overflow because of the first, subtraction,
     * step.
     */
    x -= x >> 8;
    return (png_byte)((x + 0x7fffffU) >> 24);
 }
 #ifdef PNG_16BIT_SUPPORTED
 static png_uint_16
 png_exp16bit(png_fixed_point lg2)
 {
    /* Get a 32-bit value: */
    png_uint_32 x = png_exp(lg2);
    /* Convert the 32-bit value to 0..65535 by multiplying by 65536-1: */
    x -= x >> 16;
    return (png_uint_16)((x + 32767U) >> 16);
 }
 #endif /* 16BIT */
 #endif /* FLOATING_ARITHMETIC */
 png_byte
 png_gamma_8bit_correct(unsigned int value, png_fixed_point gamma_val)
 {
    if (value > 0 && value < 255)
    {
 #     ifdef PNG_FLOATING_ARITHMETIC_SUPPORTED
          double r = floor(255*pow(value/255.,gamma_val*.00001)+.5);
          return (png_byte)r;
 #     else
          png_int_32 lg2 = png_log8bit(value);
          png_fixed_point res;
          if (png_muldiv(&res, gamma_val, lg2, PNG_FP_1))
             return png_exp8bit(res);
          /* Overflow. */
          value = 0;
 #     endif
    }
    return (png_byte)value;
 }
 #ifdef PNG_16BIT_SUPPORTED
 png_uint_16
 png_gamma_16bit_correct(unsigned int value, png_fixed_point gamma_val)
 {
    if (value > 0 && value < 65535)
    {
 #     ifdef PNG_FLOATING_ARITHMETIC_SUPPORTED
          double r = floor(65535*pow(value/65535.,gamma_val*.00001)+.5);
          return (png_uint_16)r;
 #     else
          png_int_32 lg2 = png_log16bit(value);
          png_fixed_point res;
          if (png_muldiv(&res, gamma_val, lg2, PNG_FP_1))
             return png_exp16bit(res);
          /* Overflow. */
          value = 0;
 #     endif
    }
    return (png_uint_16)value;
 }
 #endif /* 16BIT */
 /* This does the right thing based on the bit_depth field of the
  * png_struct, interpreting values as 8-bit or 16-bit.  While the result
  * is nominally a 16-bit value if bit depth is 8 then the result is
  * 8-bit (as are the arguments.)
  */
 png_uint_16 /* PRIVATE */
 png_gamma_correct(png_structrp png_ptr, unsigned int value,
     png_fixed_point gamma_val)
 {
    if (png_ptr->bit_depth == 8)
       return png_gamma_8bit_correct(value, gamma_val);
 #ifdef PNG_16BIT_SUPPORTED
    else
       return png_gamma_16bit_correct(value, gamma_val);
 #else
       /* should not reach this */
       return 0;
 #endif /* 16BIT */
 }
 #ifdef PNG_16BIT_SUPPORTED
 /* Internal function to build a single 16-bit table - the table consists of
  * 'num' 256 entry subtables, where 'num' is determined by 'shift' - the amount
  * to shift the input values right (or 16-number_of_signifiant_bits).
  *
  * The caller is responsible for ensuring that the table gets cleaned up on
  * png_error (i.e. if one of the mallocs below fails) - i.e. the *table argument
  * should be somewhere that will be cleaned.
  */
 static void
 png_build_16bit_table(png_structrp png_ptr, png_uint_16pp *ptable,
    PNG_CONST unsigned int shift, PNG_CONST png_fixed_point gamma_val)
 {
    /* Various values derived from 'shift': */
    PNG_CONST unsigned int num = 1U << (8U - shift);
    PNG_CONST unsigned int max = (1U << (16U - shift))-1U;
    PNG_CONST unsigned int max_by_2 = 1U << (15U-shift);
    unsigned int i;
    png_uint_16pp table = *ptable =
        (png_uint_16pp)png_calloc(png_ptr, num * (sizeof (png_uint_16p)));
    for (i = 0; i < num; i++)
    {
       png_uint_16p sub_table = table[i] =
           (png_uint_16p)png_malloc(png_ptr, 256 * (sizeof (png_uint_16)));
       /* The 'threshold' test is repeated here because it can arise for one of
        * the 16-bit tables even if the others don't hit it.
        */
       if (png_gamma_significant(gamma_val))
       {
          /* The old code would overflow at the end and this would cause the
           * 'pow' function to return a result >1, resulting in an
           * arithmetic error.  This code follows the spec exactly; ig is
           * the recovered input sample, it always has 8-16 bits.
           *
           * We want input * 65535/max, rounded, the arithmetic fits in 32
           * bits (unsigned) so long as max <= 32767.
           */
          unsigned int j;
          for (j = 0; j < 256; j++)
          {
             png_uint_32 ig = (j << (8-shift)) + i;
 #           ifdef PNG_FLOATING_ARITHMETIC_SUPPORTED
                /* Inline the 'max' scaling operation: */
                double d = floor(65535*pow(ig/(double)max, gamma_val*.00001)+.5);
                sub_table[j] = (png_uint_16)d;
 #           else
                if (shift)
                   ig = (ig * 65535U + max_by_2)/max;
                sub_table[j] = png_gamma_16bit_correct(ig, gamma_val);
 #           endif
          }
       }
       else
       {
          /* We must still build a table, but do it the fast way. */
          unsigned int j;
          for (j = 0; j < 256; j++)
          {
             png_uint_32 ig = (j << (8-shift)) + i;
             if (shift)
                ig = (ig * 65535U + max_by_2)/max;
             sub_table[j] = (png_uint_16)ig;
          }
       }
    }
 }
 /* NOTE: this function expects the *inverse* of the overall gamma transformation
  * required.
  */
 static void
 png_build_16to8_table(png_structrp png_ptr, png_uint_16pp *ptable,
    PNG_CONST unsigned int shift, PNG_CONST png_fixed_point gamma_val)
 {
    PNG_CONST unsigned int num = 1U << (8U - shift);
    PNG_CONST unsigned int max = (1U << (16U - shift))-1U;
    unsigned int i;
    png_uint_32 last;
    png_uint_16pp table = *ptable =
        (png_uint_16pp)png_calloc(png_ptr, num * (sizeof (png_uint_16p)));
    /* 'num' is the number of tables and also the number of low bits of low
     * bits of the input 16-bit value used to select a table.  Each table is
     * itself index by the high 8 bits of the value.
     */
    for (i = 0; i < num; i++)
       table[i] = (png_uint_16p)png_malloc(png_ptr,
 * (sizeof (png_uint_16)));
    /* 'gamma_val' is set to the reciprocal of the value calculated above, so
     * pow(out,g) is an *input* value.  'last' is the last input value set.
     *
     * In the loop 'i' is used to find output values.  Since the output is
     * 8-bit there are only 256 possible values.  The tables are set up to
     * select the closest possible output value for each input by finding
     * the input value at the boundary between each pair of output values
     * and filling the table up to that boundary with the lower output
     * value.
     *
     * The boundary values are 0.5,1.5..253.5,254.5.  Since these are 9-bit
     * values the code below uses a 16-bit value in i; the values start at
     * 128.5 (for 0.5) and step by 257, for a total of 254 values (the last
     * entries are filled with 255).  Start i at 128 and fill all 'last'
     * table entries <= 'max'
     */
    last = 0;
    for (i = 0; i < 255; ++i) /* 8-bit output value */
    {
       /* Find the corresponding maximum input value */
       png_uint_16 out = (png_uint_16)(i * 257U); /* 16-bit output value */
       /* Find the boundary value in 16 bits: */
       png_uint_32 bound = png_gamma_16bit_correct(out+128U, gamma_val);
       /* Adjust (round) to (16-shift) bits: */
       bound = (bound * max + 32768U)/65535U + 1U;
       while (last < bound)
       {
          table[last & (0xffU >> shift)][last >> (8U - shift)] = out;
          last++;
       }
    }
    /* And fill in the final entries. */
    while (last < (num << 8))
    {
       table[last & (0xff >> shift)][last >> (8U - shift)] = 65535U;
       last++;
    }
 }
 #endif /* 16BIT */
 /* Build a single 8-bit table: same as the 16-bit case but much simpler (and
  * typically much faster).  Note that libpng currently does no sBIT processing
  * (apparently contrary to the spec) so a 256 entry table is always generated.
  */
 static void
 png_build_8bit_table(png_structrp png_ptr, png_bytepp ptable,
    PNG_CONST png_fixed_point gamma_val)
 {
    unsigned int i;
    png_bytep table = *ptable = (png_bytep)png_malloc(png_ptr, 256);
    if (png_gamma_significant(gamma_val)) for (i=0; i<256; i++)
       table[i] = png_gamma_8bit_correct(i, gamma_val);
    else for (i=0; i<256; ++i)
       table[i] = (png_byte)i;
 }
 /* Used from png_read_destroy and below to release the memory used by the gamma
  * tables.
  */
 void /* PRIVATE */
 png_destroy_gamma_table(png_structrp png_ptr)
 {
    png_free(png_ptr, png_ptr->gamma_table);
    png_ptr->gamma_table = NULL;
 #ifdef PNG_16BIT_SUPPORTED
    if (png_ptr->gamma_16_table != NULL)
    {
       int i;
       int istop = (1 << (8 - png_ptr->gamma_shift));
       for (i = 0; i < istop; i++)
       {
          png_free(png_ptr, png_ptr->gamma_16_table[i]);
       }
    png_free(png_ptr, png_ptr->gamma_16_table);
    png_ptr->gamma_16_table = NULL;
    }
 #endif /* 16BIT */
 #if defined(PNG_READ_BACKGROUND_SUPPORTED) || \
    defined(PNG_READ_ALPHA_MODE_SUPPORTED) || \
    defined(PNG_READ_RGB_TO_GRAY_SUPPORTED)
    png_free(png_ptr, png_ptr->gamma_from_1);
    png_ptr->gamma_from_1 = NULL;
    png_free(png_ptr, png_ptr->gamma_to_1);
    png_ptr->gamma_to_1 = NULL;
 #ifdef PNG_16BIT_SUPPORTED
    if (png_ptr->gamma_16_from_1 != NULL)
    {
       int i;
       int istop = (1 << (8 - png_ptr->gamma_shift));
       for (i = 0; i < istop; i++)
       {
          png_free(png_ptr, png_ptr->gamma_16_from_1[i]);
       }
    png_free(png_ptr, png_ptr->gamma_16_from_1);
    png_ptr->gamma_16_from_1 = NULL;
    }
    if (png_ptr->gamma_16_to_1 != NULL)
    {
       int i;
       int istop = (1 << (8 - png_ptr->gamma_shift));
       for (i = 0; i < istop; i++)
       {
          png_free(png_ptr, png_ptr->gamma_16_to_1[i]);
       }
    png_free(png_ptr, png_ptr->gamma_16_to_1);
    png_ptr->gamma_16_to_1 = NULL;
    }
 #endif /* 16BIT */
 #endif /* READ_BACKGROUND || READ_ALPHA_MODE || RGB_TO_GRAY */
 }
 /* We build the 8- or 16-bit gamma tables here.  Note that for 16-bit
  * tables, we don't make a full table if we are reducing to 8-bit in
  * the future.  Note also how the gamma_16 tables are segmented so that
  * we don't need to allocate > 64K chunks for a full 16-bit table.
  */
 void /* PRIVATE */
 png_build_gamma_table(png_structrp png_ptr, int bit_depth)
 {
   png_debug(1, "in png_build_gamma_table");
   /* Remove any existing table; this copes with multiple calls to
    * png_read_update_info.  The warning is because building the gamma tables
    * multiple times is a performance hit - it's harmless but the ability to call
    * png_read_update_info() multiple times is new in 1.5.6 so it seems sensible
    * to warn if the app introduces such a hit.
    */
   if (png_ptr->gamma_table != NULL || png_ptr->gamma_16_table != NULL)
   {
     png_warning(png_ptr, "gamma table being rebuilt");
     png_destroy_gamma_table(png_ptr);
   }
   if (bit_depth <= 8)
   {
      png_build_8bit_table(png_ptr, &png_ptr->gamma_table,
          png_ptr->screen_gamma > 0 ?  png_reciprocal2(png_ptr->colorspace.gamma,
          png_ptr->screen_gamma) : PNG_FP_1);
 #if defined(PNG_READ_BACKGROUND_SUPPORTED) || \
    defined(PNG_READ_ALPHA_MODE_SUPPORTED) || \
    defined(PNG_READ_RGB_TO_GRAY_SUPPORTED)
      if (png_ptr->transformations & (PNG_COMPOSE | PNG_RGB_TO_GRAY))
      {
         png_build_8bit_table(png_ptr, &png_ptr->gamma_to_1,
             png_reciprocal(png_ptr->colorspace.gamma));
         png_build_8bit_table(png_ptr, &png_ptr->gamma_from_1,
             png_ptr->screen_gamma > 0 ?  png_reciprocal(png_ptr->screen_gamma) :
             png_ptr->colorspace.gamma/* Probably doing rgb_to_gray */);
      }
 #endif /* READ_BACKGROUND || READ_ALPHA_MODE || RGB_TO_GRAY */
   }
 #ifdef PNG_16BIT_SUPPORTED
   else
   {
      png_byte shift, sig_bit;
      if (png_ptr->color_type & PNG_COLOR_MASK_COLOR)
      {
         sig_bit = png_ptr->sig_bit.red;
         if (png_ptr->sig_bit.green > sig_bit)
            sig_bit = png_ptr->sig_bit.green;
         if (png_ptr->sig_bit.blue > sig_bit)
            sig_bit = png_ptr->sig_bit.blue;
      }
      else
         sig_bit = png_ptr->sig_bit.gray;
      /* 16-bit gamma code uses this equation:
       *
       *   ov = table[(iv & 0xff) >> gamma_shift][iv >> 8]
       *
       * Where 'iv' is the input color value and 'ov' is the output value -
       * pow(iv, gamma).
       *
       * Thus the gamma table consists of up to 256 256 entry tables.  The table
       * is selected by the (8-gamma_shift) most significant of the low 8 bits of
       * the color value then indexed by the upper 8 bits:
       *
       *   table[low bits][high 8 bits]
       *
       * So the table 'n' corresponds to all those 'iv' of:
       *
       *   <all high 8-bit values><n << gamma_shift>..<(n+1 << gamma_shift)-1>
       *
       */
      if (sig_bit > 0 && sig_bit < 16U)
         shift = (png_byte)(16U - sig_bit); /* shift == insignificant bits */
      else
         shift = 0; /* keep all 16 bits */
      if (png_ptr->transformations & (PNG_16_TO_8 | PNG_SCALE_16_TO_8))
      {
         /* PNG_MAX_GAMMA_8 is the number of bits to keep - effectively
          * the significant bits in the *input* when the output will
          * eventually be 8 bits.  By default it is 11.
          */
         if (shift < (16U - PNG_MAX_GAMMA_8))
            shift = (16U - PNG_MAX_GAMMA_8);
      }
      if (shift > 8U)
         shift = 8U; /* Guarantees at least one table! */
      png_ptr->gamma_shift = shift;
      /* NOTE: prior to 1.5.4 this test used to include PNG_BACKGROUND (now
       * PNG_COMPOSE).  This effectively smashed the background calculation for
       * 16-bit output because the 8-bit table assumes the result will be reduced
       * to 8 bits.
       */
      if (png_ptr->transformations & (PNG_16_TO_8 | PNG_SCALE_16_TO_8))
          png_build_16to8_table(png_ptr, &png_ptr->gamma_16_table, shift,
          png_ptr->screen_gamma > 0 ? png_product2(png_ptr->colorspace.gamma,
          png_ptr->screen_gamma) : PNG_FP_1);
      else
          png_build_16bit_table(png_ptr, &png_ptr->gamma_16_table, shift,
          png_ptr->screen_gamma > 0 ? png_reciprocal2(png_ptr->colorspace.gamma,
          png_ptr->screen_gamma) : PNG_FP_1);
 #if defined(PNG_READ_BACKGROUND_SUPPORTED) || \
    defined(PNG_READ_ALPHA_MODE_SUPPORTED) || \
    defined(PNG_READ_RGB_TO_GRAY_SUPPORTED)
      if (png_ptr->transformations & (PNG_COMPOSE | PNG_RGB_TO_GRAY))
      {
         png_build_16bit_table(png_ptr, &png_ptr->gamma_16_to_1, shift,
             png_reciprocal(png_ptr->colorspace.gamma));
         /* Notice that the '16 from 1' table should be full precision, however
          * the lookup on this table still uses gamma_shift, so it can't be.
          * TODO: fix this.
          */
         png_build_16bit_table(png_ptr, &png_ptr->gamma_16_from_1, shift,
             png_ptr->screen_gamma > 0 ? png_reciprocal(png_ptr->screen_gamma) :
             png_ptr->colorspace.gamma/* Probably doing rgb_to_gray */);
      }
 #endif /* READ_BACKGROUND || READ_ALPHA_MODE || RGB_TO_GRAY */
   }
 #endif /* 16BIT */
 }
 #endif /* READ_GAMMA */
 /* HARDWARE OPTION SUPPORT */
 #ifdef PNG_SET_OPTION_SUPPORTED
 int PNGAPI
 png_set_option(png_structrp png_ptr, int option, int onoff)
 {
    if (png_ptr != NULL && option >= 0 && option < PNG_OPTION_NEXT &&
       (option & 1) == 0)
    {
       int mask = 3 << option;
       int setting = (2 + (onoff != 0)) << option;
       int current = png_ptr->options;
       png_ptr->options = (png_byte)((current & ~mask) | setting);
       return (current & mask) >> option;
    }
    return PNG_OPTION_INVALID;
 }
 #endif
 /* sRGB support */
 #if defined(PNG_SIMPLIFIED_READ_SUPPORTED) ||\
    defined(PNG_SIMPLIFIED_WRITE_SUPPORTED)
 /* sRGB conversion tables; these are machine generated with the code in
  * contrib/tools/makesRGB.c.  The actual sRGB transfer curve defined in the
  * specification (see the article at http://en.wikipedia.org/wiki/SRGB)
  * is used, not the gamma=1/2.2 approximation use elsewhere in libpng.
  * The sRGB to linear table is exact (to the nearest 16 bit linear fraction).
  * The inverse (linear to sRGB) table has accuracies as follows:
  *
  * For all possible (255*65535+1) input values:
  *
  *    error: -0.515566 - 0.625971, 79441 (0.475369%) of readings inexact
  *
  * For the input values corresponding to the 65536 16-bit values:
  *
  *    error: -0.513727 - 0.607759, 308 (0.469978%) of readings inexact
  *
  * In all cases the inexact readings are off by one.
  */
 #ifdef PNG_SIMPLIFIED_READ_SUPPORTED
 /* The convert-to-sRGB table is only currently required for read. */
 const png_uint_16 png_sRGB_table[256] =
 {
 ,20,40,60,80,99,119,139,
 ,179,199,219,241,264,288,313,
 ,367,396,427,458,491,526,562,
 ,637,677,718,761,805,851,898,
 ,997,1048,1101,1156,1212,1270,1330,
 ,1453,1517,1583,1651,1720,1790,1863,
 ,2013,2090,2170,2250,2333,2418,2504,
 ,2681,2773,2866,2961,3058,3157,3258,
 ,3464,3570,3678,3788,3900,4014,4129,
 ,4366,4488,4611,4736,4864,4993,5124,
 ,5392,5530,5669,5810,5953,6099,6246,
 ,6547,6700,6856,7014,7174,7335,7500,
 ,7834,8004,8177,8352,8528,8708,8889,
 ,9258,9445,9635,9828,10022,10219,10417,
 ,10822,11028,11235,11446,11658,11873,12090,
 ,12530,12754,12980,13209,13440,13673,13909,
 ,14387,14629,14874,15122,15371,15623,15878,
 ,16394,16656,16920,17187,17456,17727,18001,
 ,18556,18837,19121,19407,19696,19987,20281,
 ,20876,21177,21481,21787,22096,22407,22721,
 ,23357,23678,24002,24329,24658,24990,25325,
 ,26001,26344,26688,27036,27386,27739,28094,
 ,28813,29176,29542,29911,30282,30656,31033,
 ,31794,32179,32567,32957,33350,33745,34143,
 ,34948,35355,35764,36176,36591,37008,37429,
 ,38278,38706,39138,39572,40009,40449,40891,
 ,41785,42236,42690,43147,43606,44069,44534,
 ,45473,45947,46423,46903,47385,47871,48359,
 ,49344,49841,50341,50844,51349,51858,52369,
 ,53401,53921,54445,54971,55500,56032,56567,
 ,57646,58190,58737,59287,59840,60396,60955,
 ,62082,62650,63221,63795,64372,64952,65535
 };
 #endif /* simplified read only */
 /* The base/delta tables are required for both read and write (but currently
  * only the simplified versions.)
  */
 const png_uint_16 png_sRGB_base[512] =
 {
 ,1782,3383,4644,5675,6564,7357,8074,
 ,9346,9921,10463,10977,11466,11935,12384,
 ,13233,13634,14024,14402,14769,15125,15473,
 ,16142,16466,16781,17090,17393,17690,17981,
 ,18546,18822,19093,19359,19621,19879,20133,
 ,20630,20873,21113,21349,21583,21813,22041,
 ,22487,22707,22923,23138,23350,23559,23767,
 ,24175,24376,24575,24772,24967,25160,25352,
 ,25730,25916,26101,26284,26465,26645,26823,
 ,27176,27350,27523,27695,27865,28034,28201,
 ,28533,28697,28860,29021,29182,29341,29500,
 ,29813,29969,30123,30276,30429,30580,30730,
 ,31028,31176,31323,31469,31614,31758,31902,
 ,32186,32327,32468,32607,32746,32884,33021,
 ,33294,33429,33564,33697,33831,33963,34095,
 ,34357,34486,34616,34744,34873,35000,35127,
 ,35379,35504,35629,35753,35876,35999,36122,
 ,36365,36486,36606,36726,36845,36964,37083,
 ,37318,37435,37551,37668,37783,37898,38013,
 ,38241,38354,38467,38580,38692,38803,38915,
 ,39136,39246,39356,39465,39574,39682,39790,
 ,40005,40112,40219,40325,40431,40537,40642,
 ,40851,40955,41059,41163,41266,41369,41471,
 ,41675,41777,41878,41979,42079,42179,42279,
 ,42478,42577,42676,42775,42873,42971,43068,
 ,43262,43359,43456,43552,43648,43743,43839,
 ,44028,44123,44217,44311,44405,44499,44592,
 ,44778,44870,44962,45054,45146,45238,45329,
 ,45511,45601,45692,45782,45872,45961,46051,
 ,46229,46318,46406,46494,46583,46670,46758,
 ,46933,47020,47107,47193,47280,47366,47452,
 ,47623,47709,47794,47879,47964,48048,48133,
 ,48301,48385,48468,48552,48635,48718,48801,
 ,48966,49048,49131,49213,49294,49376,49458,
 ,49620,49701,49782,49862,49943,50023,50103,
 ,50263,50342,50422,50501,50580,50659,50738,
 ,50895,50973,51051,51129,51207,51285,51362,
 ,51517,51594,51671,51747,51824,51900,51977,
 ,52129,52205,52280,52356,52432,52507,52582,
 ,52732,52807,52881,52956,53030,53104,53178,
 ,53326,53400,53473,53546,53620,53693,53766,
 ,53911,53984,54056,54129,54201,54273,54345,
 ,54489,54560,54632,54703,54774,54845,54916,
 ,55058,55129,55199,55269,55340,55410,55480,
 ,55620,55689,55759,55828,55898,55967,56036,
 ,56174,56243,56311,56380,56448,56517,56585,
 ,56721,56789,56857,56924,56992,57059,57127,
 ,57261,57328,57395,57462,57529,57595,57662,
 ,57795,57861,57927,57993,58059,58125,58191,
 ,58322,58387,58453,58518,58583,58648,58713,
 ,58843,58908,58972,59037,59101,59165,59230,
 ,59358,59422,59486,59549,59613,59677,59740,
 ,59867,59930,59993,60056,60119,60182,60245,
 ,60370,60433,60495,60558,60620,60682,60744,
 ,60868,60930,60992,61054,61115,61177,61238,
 ,61361,61422,61483,61544,61605,61666,61727,
 ,61848,61909,61969,62030,62090,62150,62211,
 ,62331,62391,62450,62510,62570,62630,62689,
 ,62808,62867,62927,62986,63045,63104,63163,
 ,63281,63340,63398,63457,63515,63574,63632,
 ,63749,63807,63865,63923,63981,64039,64097,
 ,64212,64270,64328,64385,64443,64500,64557,
 ,64672,64729,64786,64843,64900,64956,65013,
 ,65126,65183,65239,65296,65352,65409,65465
 };
 const png_byte png_sRGB_delta[512] =
 {
 ,201,158,129,113,100,90,82,77,72,68,64,61,59,56,54,
 ,50,49,47,46,45,43,42,41,40,39,39,38,37,36,36,
 ,34,34,33,33,32,32,31,31,30,30,30,29,29,28,28,
 ,27,27,27,27,26,26,26,25,25,25,25,24,24,24,24,
 ,23,23,23,23,22,22,22,22,22,22,21,21,21,21,21,
 ,20,20,20,20,20,20,20,20,19,19,19,19,19,19,19,
 ,18,18,18,18,18,18,18,18,18,18,17,17,17,17,17,
 ,17,17,17,17,17,16,16,16,16,16,16,16,16,16,16,
 ,16,16,16,15,15,15,15,15,15,15,15,15,15,15,15,
 ,15,15,15,14,14,14,14,14,14,14,14,14,14,14,14,
 ,14,14,14,14,14,14,13,13,13,13,13,13,13,13,13,
 ,13,13,13,13,13,13,13,13,13,13,13,13,13,12,12,
 ,12,12,12,12,12,12,12,12,12,12,12,12,12,12,12,
 ,12,12,12,12,12,12,12,12,12,12,12,11,11,11,11,
 ,11,11,11,11,11,11,11,11,11,11,11,11,11,11,11,
 ,11,11,11,11,11,11,11,11,11,11,11,11,11,11,11,
 ,10,10,10,10,10,10,10,10,10,10,10,10,10,10,10,
 ,10,10,10,10,10,10,10,10,10,10,10,10,10,10,10,
 ,10,10,10,10,10,10,10,10,10,10,10,10,10,10,10,
 ,9,9,9,9,9,9,9,9,9,9,9,9,9,9,9,
 ,9,9,9,9,9,9,9,9,9,9,9,9,9,9,9,
 ,9,9,9,9,9,9,9,9,9,9,9,9,9,9,9,
 ,9,9,9,9,9,9,9,9,9,9,9,9,9,9,9,
 ,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,
 ,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,
 ,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,
 ,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,
 ,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,
 ,8,8,8,8,8,8,8,8,7,7,7,7,7,7,7,
 ,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,
 ,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,
 ,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7
 };
 #endif /* SIMPLIFIED READ/WRITE sRGB support */
 /* SIMPLIFIED READ/WRITE SUPPORT */
 #if defined(PNG_SIMPLIFIED_READ_SUPPORTED) ||\
    defined(PNG_SIMPLIFIED_WRITE_SUPPORTED)
 static int
 png_image_free_function(png_voidp argument)
 {
    png_imagep image = png_voidcast(png_imagep, argument);
    png_controlp cp = image->opaque;
    png_control c;
    /* Double check that we have a png_ptr - it should be impossible to get here
     * without one.
     */
    if (cp->png_ptr == NULL)
       return 0;
    /* First free any data held in the control structure. */
 #  ifdef PNG_STDIO_SUPPORTED
       if (cp->owned_file)
       {
          FILE *fp = png_voidcast(FILE*, cp->png_ptr->io_ptr);
          cp->owned_file = 0;
          /* Ignore errors here. */
          if (fp != NULL)
          {
             cp->png_ptr->io_ptr = NULL;
             (void)fclose(fp);
          }
       }
 #  endif
    /* Copy the control structure so that the original, allocated, version can be
     * safely freed.  Notice that a png_error here stops the remainder of the
     * cleanup, but this is probably fine because that would indicate bad memory
     * problems anyway.
     */
    c = *cp;
    image->opaque = &c;
    png_free(c.png_ptr, cp);
    /* Then the structures, calling the correct API. */
    if (c.for_write)
    {
 #     ifdef PNG_SIMPLIFIED_WRITE_SUPPORTED
          png_destroy_write_struct(&c.png_ptr, &c.info_ptr);
 #     else
          png_error(c.png_ptr, "simplified write not supported");
 #     endif
    }
    else
    {
 #     ifdef PNG_SIMPLIFIED_READ_SUPPORTED
          png_destroy_read_struct(&c.png_ptr, &c.info_ptr, NULL);
 #     else
          png_error(c.png_ptr, "simplified read not supported");
 #     endif
    }
    /* Success. */
    return 1;
 }
 void PNGAPI
 png_image_free(png_imagep image)
 {
    /* Safely call the real function, but only if doing so is safe at this point
     * (if not inside an error handling context).  Otherwise assume
     * png_safe_execute will call this API after the return.
     */
    if (image != NULL && image->opaque != NULL &&
       image->opaque->error_buf == NULL)
    {
       /* Ignore errors here: */
       (void)png_safe_execute(image, png_image_free_function, image);
       image->opaque = NULL;
    }
 }
 int /* PRIVATE */
 png_image_error(png_imagep image, png_const_charp error_message)
 {
    /* Utility to log an error. */
    png_safecat(image->message, (sizeof image->message), 0, error_message);
    image->warning_or_error |= PNG_IMAGE_ERROR;
    png_image_free(image);
    return 0;
 }
 #endif /* SIMPLIFIED READ/WRITE */
 #endif /* defined(PNG_READ_SUPPORTED) || defined(PNG_WRITE_SUPPORTED) */

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