The Tor Browser: comparison media/libpng/png.c

--1:000000000000
+:c2eb395b4ad7
+/* 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,
+5/*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,
+100))
+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,
+2/*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.
+*/
+65166, 64430, 63700, 62976, 62257, 61543, 60835, 60132, 59434, 58741, 58054,
+57371, 56693, 56020, 55352, 54689, 54030, 53375, 52726, 52080, 51439, 50803,
+50170, 49542, 48918, 48298, 47682, 47070, 46462, 45858, 45257, 44661, 44068,
+43479, 42894, 42312, 41733, 41159, 40587, 40020, 39455, 38894, 38336, 37782,
+37230, 36682, 36137, 35595, 35057, 34521, 33988, 33459, 32932, 32408, 31887,
+31369, 30854, 30341, 29832, 29325, 28820, 28319, 27820, 27324, 26830, 26339,
+25850, 25364, 24880, 24399, 23920, 23444, 22970, 22499, 22029, 21562, 21098,
+20636, 20175, 19718, 19262, 18808, 18357, 17908, 17461, 17016, 16573, 16132,
+15694, 15257, 14822, 14390, 13959, 13530, 13103, 12678, 12255, 11834, 11415,
+10997, 10582, 10168, 9756, 9346, 8937, 8531, 8126, 7723, 7321, 6921, 6523,
+6127, 5732, 5339, 4947, 4557, 4169, 3782, 3397, 3014, 2632, 2251, 1872, 1495,
+1119, 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"}
+11 44937.64284865548751208448
+10 45180.98734845585101160448
+9 45303.31936980687359311872
+8 45364.65110595323018870784
+7 45395.35850361789624614912
+6 45410.72259715102037508096
+5 45418.40724413220722311168
+4 45422.25021786898173001728
+3 45424.17186732298419044352
+2 45425.13273269940811464704
+1 45425.61317555035558641664
+0 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,
+256 * (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] =
+{
+0,20,40,60,80,99,119,139,
+159,179,199,219,241,264,288,313,
+340,367,396,427,458,491,526,562,
+599,637,677,718,761,805,851,898,
+947,997,1048,1101,1156,1212,1270,1330,
+1391,1453,1517,1583,1651,1720,1790,1863,
+1937,2013,2090,2170,2250,2333,2418,2504,
+2592,2681,2773,2866,2961,3058,3157,3258,
+3360,3464,3570,3678,3788,3900,4014,4129,
+4247,4366,4488,4611,4736,4864,4993,5124,
+5257,5392,5530,5669,5810,5953,6099,6246,
+6395,6547,6700,6856,7014,7174,7335,7500,
+7666,7834,8004,8177,8352,8528,8708,8889,
+9072,9258,9445,9635,9828,10022,10219,10417,
+10619,10822,11028,11235,11446,11658,11873,12090,
+12309,12530,12754,12980,13209,13440,13673,13909,
+14146,14387,14629,14874,15122,15371,15623,15878,
+16135,16394,16656,16920,17187,17456,17727,18001,
+18277,18556,18837,19121,19407,19696,19987,20281,
+20577,20876,21177,21481,21787,22096,22407,22721,
+23038,23357,23678,24002,24329,24658,24990,25325,
+25662,26001,26344,26688,27036,27386,27739,28094,
+28452,28813,29176,29542,29911,30282,30656,31033,
+31412,31794,32179,32567,32957,33350,33745,34143,
+34544,34948,35355,35764,36176,36591,37008,37429,
+37852,38278,38706,39138,39572,40009,40449,40891,
+41337,41785,42236,42690,43147,43606,44069,44534,
+45002,45473,45947,46423,46903,47385,47871,48359,
+48850,49344,49841,50341,50844,51349,51858,52369,
+52884,53401,53921,54445,54971,55500,56032,56567,
+57105,57646,58190,58737,59287,59840,60396,60955,
+61517,62082,62650,63221,63795,64372,64952,65535
+};
+#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] =
+{
+128,1782,3383,4644,5675,6564,7357,8074,
+8732,9346,9921,10463,10977,11466,11935,12384,
+12816,13233,13634,14024,14402,14769,15125,15473,
+15812,16142,16466,16781,17090,17393,17690,17981,
+18266,18546,18822,19093,19359,19621,19879,20133,
+20383,20630,20873,21113,21349,21583,21813,22041,
+22265,22487,22707,22923,23138,23350,23559,23767,
+23972,24175,24376,24575,24772,24967,25160,25352,
+25542,25730,25916,26101,26284,26465,26645,26823,
+27000,27176,27350,27523,27695,27865,28034,28201,
+28368,28533,28697,28860,29021,29182,29341,29500,
+29657,29813,29969,30123,30276,30429,30580,30730,
+30880,31028,31176,31323,31469,31614,31758,31902,
+32045,32186,32327,32468,32607,32746,32884,33021,
+33158,33294,33429,33564,33697,33831,33963,34095,
+34226,34357,34486,34616,34744,34873,35000,35127,
+35253,35379,35504,35629,35753,35876,35999,36122,
+36244,36365,36486,36606,36726,36845,36964,37083,
+37201,37318,37435,37551,37668,37783,37898,38013,
+38127,38241,38354,38467,38580,38692,38803,38915,
+39026,39136,39246,39356,39465,39574,39682,39790,
+39898,40005,40112,40219,40325,40431,40537,40642,
+40747,40851,40955,41059,41163,41266,41369,41471,
+41573,41675,41777,41878,41979,42079,42179,42279,
+42379,42478,42577,42676,42775,42873,42971,43068,
+43165,43262,43359,43456,43552,43648,43743,43839,
+43934,44028,44123,44217,44311,44405,44499,44592,
+44685,44778,44870,44962,45054,45146,45238,45329,
+45420,45511,45601,45692,45782,45872,45961,46051,
+46140,46229,46318,46406,46494,46583,46670,46758,
+46846,46933,47020,47107,47193,47280,47366,47452,
+47538,47623,47709,47794,47879,47964,48048,48133,
+48217,48301,48385,48468,48552,48635,48718,48801,
+48884,48966,49048,49131,49213,49294,49376,49458,
+49539,49620,49701,49782,49862,49943,50023,50103,
+50183,50263,50342,50422,50501,50580,50659,50738,
+50816,50895,50973,51051,51129,51207,51285,51362,
+51439,51517,51594,51671,51747,51824,51900,51977,
+52053,52129,52205,52280,52356,52432,52507,52582,
+52657,52732,52807,52881,52956,53030,53104,53178,
+53252,53326,53400,53473,53546,53620,53693,53766,
+53839,53911,53984,54056,54129,54201,54273,54345,
+54417,54489,54560,54632,54703,54774,54845,54916,
+54987,55058,55129,55199,55269,55340,55410,55480,
+55550,55620,55689,55759,55828,55898,55967,56036,
+56105,56174,56243,56311,56380,56448,56517,56585,
+56653,56721,56789,56857,56924,56992,57059,57127,
+57194,57261,57328,57395,57462,57529,57595,57662,
+57728,57795,57861,57927,57993,58059,58125,58191,
+58256,58322,58387,58453,58518,58583,58648,58713,
+58778,58843,58908,58972,59037,59101,59165,59230,
+59294,59358,59422,59486,59549,59613,59677,59740,
+59804,59867,59930,59993,60056,60119,60182,60245,
+60308,60370,60433,60495,60558,60620,60682,60744,
+60806,60868,60930,60992,61054,61115,61177,61238,
+61300,61361,61422,61483,61544,61605,61666,61727,
+61788,61848,61909,61969,62030,62090,62150,62211,
+62271,62331,62391,62450,62510,62570,62630,62689,
+62749,62808,62867,62927,62986,63045,63104,63163,
+63222,63281,63340,63398,63457,63515,63574,63632,
+63691,63749,63807,63865,63923,63981,64039,64097,
+64155,64212,64270,64328,64385,64443,64500,64557,
+64614,64672,64729,64786,64843,64900,64956,65013,
+65070,65126,65183,65239,65296,65352,65409,65465
+};
+const png_byte png_sRGB_delta[512] =
+{
+207,201,158,129,113,100,90,82,77,72,68,64,61,59,56,54,
+52,50,49,47,46,45,43,42,41,40,39,39,38,37,36,36,
+35,34,34,33,33,32,32,31,31,30,30,30,29,29,28,28,
+28,27,27,27,27,26,26,26,25,25,25,25,24,24,24,24,
+23,23,23,23,23,22,22,22,22,22,22,21,21,21,21,21,
+21,20,20,20,20,20,20,20,20,19,19,19,19,19,19,19,
+19,18,18,18,18,18,18,18,18,18,18,17,17,17,17,17,
+17,17,17,17,17,17,16,16,16,16,16,16,16,16,16,16,
+16,16,16,16,15,15,15,15,15,15,15,15,15,15,15,15,
+15,15,15,15,14,14,14,14,14,14,14,14,14,14,14,14,
+14,14,14,14,14,14,14,13,13,13,13,13,13,13,13,13,
+13,13,13,13,13,13,13,13,13,13,13,13,13,13,12,12,
+12,12,12,12,12,12,12,12,12,12,12,12,12,12,12,12,
+12,12,12,12,12,12,12,12,12,12,12,12,11,11,11,11,
+11,11,11,11,11,11,11,11,11,11,11,11,11,11,11,11,
+11,11,11,11,11,11,11,11,11,11,11,11,11,11,11,11,
+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,
+10,10,10,10,10,10,10,10,10,10,10,10,10,10,10,10,
+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,
+9,9,9,9,9,9,9,9,9,9,9,9,9,9,9,9,
+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,
+8,8,8,8,8,8,8,8,8,7,7,7,7,7,7,7,
+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,
+7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7
+};
+#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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