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 /*

  * jchuff.c

  *

  * This file was part of the Independent JPEG Group's software:

  * Copyright (C) 1991-1997, Thomas G. Lane.

  * libjpeg-turbo Modifications:

  * Copyright (C) 2009-2011, D. R. Commander.

  * For conditions of distribution and use, see the accompanying README file.

  *

  * This file contains Huffman entropy encoding routines.

  *

  * Much of the complexity here has to do with supporting output suspension.

  * If the data destination module demands suspension, we want to be able to

  * back up to the start of the current MCU.  To do this, we copy state

  * variables into local working storage, and update them back to the

  * permanent JPEG objects only upon successful completion of an MCU.

  */

 #define JPEG_INTERNALS

 #include "jinclude.h"

 #include "jpeglib.h"

 #include "jchuff.h"		/* Declarations shared with jcphuff.c */

 #include <limits.h>

 static const unsigned char jpeg_nbits_table[65536] = {

 /* Number i needs jpeg_nbits_table[i] bits to be represented. */

 #include "jpeg_nbits_table.h"

 };

 #ifndef min

  #define min(a,b) ((a)<(b)?(a):(b))

 #endif

 /* Expanded entropy encoder object for Huffman encoding.

  *

  * The savable_state subrecord contains fields that change within an MCU,

  * but must not be updated permanently until we complete the MCU.

  */

 typedef struct {

   size_t put_buffer;		/* current bit-accumulation buffer */

   int put_bits;			/* # of bits now in it */

   int last_dc_val[MAX_COMPS_IN_SCAN]; /* last DC coef for each component */

 } savable_state;

 /* This macro is to work around compilers with missing or broken

  * structure assignment.  You'll need to fix this code if you have

  * such a compiler and you change MAX_COMPS_IN_SCAN.

  */

 #ifndef NO_STRUCT_ASSIGN

 #define ASSIGN_STATE(dest,src)  ((dest) = (src))

 #else

 #if MAX_COMPS_IN_SCAN == 4

 #define ASSIGN_STATE(dest,src)  \

 	((dest).put_buffer = (src).put_buffer, \

 	 (dest).put_bits = (src).put_bits, \

 	 (dest).last_dc_val[0] = (src).last_dc_val[0], \

 	 (dest).last_dc_val[1] = (src).last_dc_val[1], \

 	 (dest).last_dc_val[2] = (src).last_dc_val[2], \

 	 (dest).last_dc_val[3] = (src).last_dc_val[3])

 #endif

 #endif

 typedef struct {

   struct jpeg_entropy_encoder pub; /* public fields */

   savable_state saved;		/* Bit buffer & DC state at start of MCU */

   /* These fields are NOT loaded into local working state. */

   unsigned int restarts_to_go;	/* MCUs left in this restart interval */

   int next_restart_num;		/* next restart number to write (0-7) */

   /* Pointers to derived tables (these workspaces have image lifespan) */

   c_derived_tbl * dc_derived_tbls[NUM_HUFF_TBLS];

   c_derived_tbl * ac_derived_tbls[NUM_HUFF_TBLS];

 #ifdef ENTROPY_OPT_SUPPORTED	/* Statistics tables for optimization */

   long * dc_count_ptrs[NUM_HUFF_TBLS];

   long * ac_count_ptrs[NUM_HUFF_TBLS];

 #endif

 } huff_entropy_encoder;

 typedef huff_entropy_encoder * huff_entropy_ptr;

 /* Working state while writing an MCU.

  * This struct contains all the fields that are needed by subroutines.

  */

 typedef struct {

   JOCTET * next_output_byte;	/* => next byte to write in buffer */

   size_t free_in_buffer;	/* # of byte spaces remaining in buffer */

   savable_state cur;		/* Current bit buffer & DC state */

   j_compress_ptr cinfo;		/* dump_buffer needs access to this */

 } working_state;

 /* Forward declarations */

 METHODDEF(boolean) encode_mcu_huff JPP((j_compress_ptr cinfo,

 					JBLOCKROW *MCU_data));

 METHODDEF(void) finish_pass_huff JPP((j_compress_ptr cinfo));

 #ifdef ENTROPY_OPT_SUPPORTED

 METHODDEF(boolean) encode_mcu_gather JPP((j_compress_ptr cinfo,

 					  JBLOCKROW *MCU_data));

 METHODDEF(void) finish_pass_gather JPP((j_compress_ptr cinfo));

 #endif

 /*

  * Initialize for a Huffman-compressed scan.

  * If gather_statistics is TRUE, we do not output anything during the scan,

  * just count the Huffman symbols used and generate Huffman code tables.

  */

 METHODDEF(void)

 start_pass_huff (j_compress_ptr cinfo, boolean gather_statistics)

 {

   huff_entropy_ptr entropy = (huff_entropy_ptr) cinfo->entropy;

   int ci, dctbl, actbl;

   jpeg_component_info * compptr;

   if (gather_statistics) {

 #ifdef ENTROPY_OPT_SUPPORTED

     entropy->pub.encode_mcu = encode_mcu_gather;

     entropy->pub.finish_pass = finish_pass_gather;

 #else

     ERREXIT(cinfo, JERR_NOT_COMPILED);

 #endif

   } else {

     entropy->pub.encode_mcu = encode_mcu_huff;

     entropy->pub.finish_pass = finish_pass_huff;

   }

   for (ci = 0; ci < cinfo->comps_in_scan; ci++) {

     compptr = cinfo->cur_comp_info[ci];

     dctbl = compptr->dc_tbl_no;

     actbl = compptr->ac_tbl_no;

     if (gather_statistics) {

 #ifdef ENTROPY_OPT_SUPPORTED

       /* Check for invalid table indexes */

       /* (make_c_derived_tbl does this in the other path) */

       if (dctbl < 0 || dctbl >= NUM_HUFF_TBLS)

 	ERREXIT1(cinfo, JERR_NO_HUFF_TABLE, dctbl);

       if (actbl < 0 || actbl >= NUM_HUFF_TBLS)

 	ERREXIT1(cinfo, JERR_NO_HUFF_TABLE, actbl);

       /* Allocate and zero the statistics tables */

       /* Note that jpeg_gen_optimal_table expects 257 entries in each table! */

       if (entropy->dc_count_ptrs[dctbl] == NULL)

 	entropy->dc_count_ptrs[dctbl] = (long *)

 	  (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE,

 				      257 * SIZEOF(long));

       MEMZERO(entropy->dc_count_ptrs[dctbl], 257 * SIZEOF(long));

       if (entropy->ac_count_ptrs[actbl] == NULL)

 	entropy->ac_count_ptrs[actbl] = (long *)

 	  (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE,

 				      257 * SIZEOF(long));

       MEMZERO(entropy->ac_count_ptrs[actbl], 257 * SIZEOF(long));

 #endif

     } else {

       /* Compute derived values for Huffman tables */

       /* We may do this more than once for a table, but it's not expensive */

       jpeg_make_c_derived_tbl(cinfo, TRUE, dctbl,

 			      & entropy->dc_derived_tbls[dctbl]);

       jpeg_make_c_derived_tbl(cinfo, FALSE, actbl,

 			      & entropy->ac_derived_tbls[actbl]);

     }

     /* Initialize DC predictions to 0 */

     entropy->saved.last_dc_val[ci] = 0;

   }

   /* Initialize bit buffer to empty */

   entropy->saved.put_buffer = 0;

   entropy->saved.put_bits = 0;

   /* Initialize restart stuff */

   entropy->restarts_to_go = cinfo->restart_interval;

   entropy->next_restart_num = 0;

 }

 /*

  * Compute the derived values for a Huffman table.

  * This routine also performs some validation checks on the table.

  *

  * Note this is also used by jcphuff.c.

  */

 GLOBAL(void)

 jpeg_make_c_derived_tbl (j_compress_ptr cinfo, boolean isDC, int tblno,

 			 c_derived_tbl ** pdtbl)

 {

   JHUFF_TBL *htbl;

   c_derived_tbl *dtbl;

   int p, i, l, lastp, si, maxsymbol;

   char huffsize[257];

   unsigned int huffcode[257];

   unsigned int code;

   /* Note that huffsize[] and huffcode[] are filled in code-length order,

    * paralleling the order of the symbols themselves in htbl->huffval[].

    */

   /* Find the input Huffman table */

   if (tblno < 0 || tblno >= NUM_HUFF_TBLS)

     ERREXIT1(cinfo, JERR_NO_HUFF_TABLE, tblno);

   htbl =

     isDC ? cinfo->dc_huff_tbl_ptrs[tblno] : cinfo->ac_huff_tbl_ptrs[tblno];

   if (htbl == NULL)

     ERREXIT1(cinfo, JERR_NO_HUFF_TABLE, tblno);

   /* Allocate a workspace if we haven't already done so. */

   if (*pdtbl == NULL)

     *pdtbl = (c_derived_tbl *)

       (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE,

 				  SIZEOF(c_derived_tbl));

   dtbl = *pdtbl;

   /* Figure C.1: make table of Huffman code length for each symbol */

   p = 0;

   for (l = 1; l <= 16; l++) {

     i = (int) htbl->bits[l];

     if (i < 0 || p + i > 256)	/* protect against table overrun */

       ERREXIT(cinfo, JERR_BAD_HUFF_TABLE);

     while (i--)

       huffsize[p++] = (char) l;

   }

   huffsize[p] = 0;

   lastp = p;

   /* Figure C.2: generate the codes themselves */

   /* We also validate that the counts represent a legal Huffman code tree. */

   code = 0;

   si = huffsize[0];

   p = 0;

   while (huffsize[p]) {

     while (((int) huffsize[p]) == si) {

       huffcode[p++] = code;

       code++;

     }

     /* code is now 1 more than the last code used for codelength si; but

      * it must still fit in si bits, since no code is allowed to be all ones.

      */

     if (((INT32) code) >= (((INT32) 1) << si))

       ERREXIT(cinfo, JERR_BAD_HUFF_TABLE);

     code <<= 1;

     si++;

   }

   /* Figure C.3: generate encoding tables */

   /* These are code and size indexed by symbol value */

   /* Set all codeless symbols to have code length 0;

    * this lets us detect duplicate VAL entries here, and later

    * allows emit_bits to detect any attempt to emit such symbols.

    */

   MEMZERO(dtbl->ehufsi, SIZEOF(dtbl->ehufsi));

   /* This is also a convenient place to check for out-of-range

    * and duplicated VAL entries.  We allow 0..255 for AC symbols

    * but only 0..15 for DC.  (We could constrain them further

    * based on data depth and mode, but this seems enough.)

    */

   maxsymbol = isDC ? 15 : 255;

   for (p = 0; p < lastp; p++) {

     i = htbl->huffval[p];

     if (i < 0 || i > maxsymbol || dtbl->ehufsi[i])

       ERREXIT(cinfo, JERR_BAD_HUFF_TABLE);

     dtbl->ehufco[i] = huffcode[p];

     dtbl->ehufsi[i] = huffsize[p];

   }

 }

 /* Outputting bytes to the file */

 /* Emit a byte, taking 'action' if must suspend. */

 #define emit_byte(state,val,action)  \

 	{ *(state)->next_output_byte++ = (JOCTET) (val);  \

 	  if (--(state)->free_in_buffer == 0)  \

 	    if (! dump_buffer(state))  \

 	      { action; } }

 LOCAL(boolean)

 dump_buffer (working_state * state)

 /* Empty the output buffer; return TRUE if successful, FALSE if must suspend */

 {

   struct jpeg_destination_mgr * dest = state->cinfo->dest;

   if (! (*dest->empty_output_buffer) (state->cinfo))

     return FALSE;

   /* After a successful buffer dump, must reset buffer pointers */

   state->next_output_byte = dest->next_output_byte;

   state->free_in_buffer = dest->free_in_buffer;

   return TRUE;

 }

 /* Outputting bits to the file */

 /* These macros perform the same task as the emit_bits() function in the

  * original libjpeg code.  In addition to reducing overhead by explicitly

  * inlining the code, additional performance is achieved by taking into

  * account the size of the bit buffer and waiting until it is almost full

  * before emptying it.  This mostly benefits 64-bit platforms, since 6

  * bytes can be stored in a 64-bit bit buffer before it has to be emptied.

  */

 #define EMIT_BYTE() { \

   JOCTET c; \

   put_bits -= 8; \

   c = (JOCTET)GETJOCTET(put_buffer >> put_bits); \

   *buffer++ = c; \

   if (c == 0xFF)  /* need to stuff a zero byte? */ \

     *buffer++ = 0; \

  }

 #define PUT_BITS(code, size) { \

   put_bits += size; \

   put_buffer = (put_buffer << size) | code; \

 }

 #define CHECKBUF15() { \

   if (put_bits > 15) { \

     EMIT_BYTE() \

     EMIT_BYTE() \

   } \

 }

 #define CHECKBUF31() { \

   if (put_bits > 31) { \

     EMIT_BYTE() \

     EMIT_BYTE() \

     EMIT_BYTE() \

     EMIT_BYTE() \

   } \

 }

 #define CHECKBUF47() { \

   if (put_bits > 47) { \

     EMIT_BYTE() \

     EMIT_BYTE() \

     EMIT_BYTE() \

     EMIT_BYTE() \

     EMIT_BYTE() \

     EMIT_BYTE() \

   } \

 }

 #if __WORDSIZE==64 || defined(_WIN64)

 #define EMIT_BITS(code, size) { \

   CHECKBUF47() \

   PUT_BITS(code, size) \

 }

 #define EMIT_CODE(code, size) { \

   temp2 &= (((INT32) 1)<<nbits) - 1; \

   CHECKBUF31() \

   PUT_BITS(code, size) \

   PUT_BITS(temp2, nbits) \

  }

 #else

 #define EMIT_BITS(code, size) { \

   PUT_BITS(code, size) \

   CHECKBUF15() \

 }

 #define EMIT_CODE(code, size) { \

   temp2 &= (((INT32) 1)<<nbits) - 1; \

   PUT_BITS(code, size) \

   CHECKBUF15() \

   PUT_BITS(temp2, nbits) \

   CHECKBUF15() \

  }

 #endif

 #define BUFSIZE (DCTSIZE2 * 2)

 #define LOAD_BUFFER() { \

   if (state->free_in_buffer < BUFSIZE) { \

     localbuf = 1; \

     buffer = _buffer; \

   } \

   else buffer = state->next_output_byte; \

  }

 #define STORE_BUFFER() { \

   if (localbuf) { \

     bytes = buffer - _buffer; \

     buffer = _buffer; \

     while (bytes > 0) { \

       bytestocopy = min(bytes, state->free_in_buffer); \

       MEMCOPY(state->next_output_byte, buffer, bytestocopy); \

       state->next_output_byte += bytestocopy; \

       buffer += bytestocopy; \

       state->free_in_buffer -= bytestocopy; \

       if (state->free_in_buffer == 0) \

         if (! dump_buffer(state)) return FALSE; \

       bytes -= bytestocopy; \

     } \

   } \

   else { \

     state->free_in_buffer -= (buffer - state->next_output_byte); \

     state->next_output_byte = buffer; \

   } \

  }

 LOCAL(boolean)

 flush_bits (working_state * state)

 {

   JOCTET _buffer[BUFSIZE], *buffer;

   size_t put_buffer;  int put_bits;

   size_t bytes, bytestocopy;  int localbuf = 0;

   put_buffer = state->cur.put_buffer;

   put_bits = state->cur.put_bits;

   LOAD_BUFFER()

   /* fill any partial byte with ones */

   PUT_BITS(0x7F, 7)

   while (put_bits >= 8) EMIT_BYTE()

   state->cur.put_buffer = 0;	/* and reset bit-buffer to empty */

   state->cur.put_bits = 0;

   STORE_BUFFER()

   return TRUE;

 }

 /* Encode a single block's worth of coefficients */

 LOCAL(boolean)

 encode_one_block (working_state * state, JCOEFPTR block, int last_dc_val,

 		  c_derived_tbl *dctbl, c_derived_tbl *actbl)

 {

   int temp, temp2, temp3;

   int nbits;

   int r, code, size;

   JOCTET _buffer[BUFSIZE], *buffer;

   size_t put_buffer;  int put_bits;

   int code_0xf0 = actbl->ehufco[0xf0], size_0xf0 = actbl->ehufsi[0xf0];

   size_t bytes, bytestocopy;  int localbuf = 0;

   put_buffer = state->cur.put_buffer;

   put_bits = state->cur.put_bits;

   LOAD_BUFFER()

   /* Encode the DC coefficient difference per section F.1.2.1 */

   temp = temp2 = block[0] - last_dc_val;

  /* This is a well-known technique for obtaining the absolute value without a

   * branch.  It is derived from an assembly language technique presented in

   * "How to Optimize for the Pentium Processors", Copyright (c) 1996, 1997 by

   * Agner Fog.

   */

   temp3 = temp >> (CHAR_BIT * sizeof(int) - 1);

   temp ^= temp3;

   temp -= temp3;

   /* For a negative input, want temp2 = bitwise complement of abs(input) */

   /* This code assumes we are on a two's complement machine */

   temp2 += temp3;

   /* Find the number of bits needed for the magnitude of the coefficient */

   nbits = jpeg_nbits_table[temp];

   /* Emit the Huffman-coded symbol for the number of bits */

   code = dctbl->ehufco[nbits];

   size = dctbl->ehufsi[nbits];

   PUT_BITS(code, size)

   CHECKBUF15()

   /* Mask off any extra bits in code */

   temp2 &= (((INT32) 1)<<nbits) - 1;

   /* Emit that number of bits of the value, if positive, */

   /* or the complement of its magnitude, if negative. */

   PUT_BITS(temp2, nbits)

   CHECKBUF15()

   /* Encode the AC coefficients per section F.1.2.2 */

   r = 0;			/* r = run length of zeros */

 /* Manually unroll the k loop to eliminate the counter variable.  This

  * improves performance greatly on systems with a limited number of

  * registers (such as x86.)

  */

 #define kloop(jpeg_natural_order_of_k) {  \

   if ((temp = block[jpeg_natural_order_of_k]) == 0) { \

     r++; \

   } else { \

     temp2 = temp; \

     /* Branch-less absolute value, bitwise complement, etc., same as above */ \

     temp3 = temp >> (CHAR_BIT * sizeof(int) - 1); \

     temp ^= temp3; \

     temp -= temp3; \

     temp2 += temp3; \

     nbits = jpeg_nbits_table[temp]; \

     /* if run length > 15, must emit special run-length-16 codes (0xF0) */ \

     while (r > 15) { \

       EMIT_BITS(code_0xf0, size_0xf0) \

       r -= 16; \

     } \

     /* Emit Huffman symbol for run length / number of bits */ \

     temp3 = (r << 4) + nbits;  \

     code = actbl->ehufco[temp3]; \

     size = actbl->ehufsi[temp3]; \

     EMIT_CODE(code, size) \

     r = 0;  \

   } \

 }

   /* One iteration for each value in jpeg_natural_order[] */

   kloop(1);   kloop(8);   kloop(16);  kloop(9);   kloop(2);   kloop(3);

   kloop(10);  kloop(17);  kloop(24);  kloop(32);  kloop(25);  kloop(18);

   kloop(11);  kloop(4);   kloop(5);   kloop(12);  kloop(19);  kloop(26);

   kloop(33);  kloop(40);  kloop(48);  kloop(41);  kloop(34);  kloop(27);

   kloop(20);  kloop(13);  kloop(6);   kloop(7);   kloop(14);  kloop(21);

   kloop(28);  kloop(35);  kloop(42);  kloop(49);  kloop(56);  kloop(57);

   kloop(50);  kloop(43);  kloop(36);  kloop(29);  kloop(22);  kloop(15);

   kloop(23);  kloop(30);  kloop(37);  kloop(44);  kloop(51);  kloop(58);

   kloop(59);  kloop(52);  kloop(45);  kloop(38);  kloop(31);  kloop(39);

   kloop(46);  kloop(53);  kloop(60);  kloop(61);  kloop(54);  kloop(47);

   kloop(55);  kloop(62);  kloop(63);

   /* If the last coef(s) were zero, emit an end-of-block code */

   if (r > 0) {

     code = actbl->ehufco[0];

     size = actbl->ehufsi[0];

     EMIT_BITS(code, size)

   }

   state->cur.put_buffer = put_buffer;

   state->cur.put_bits = put_bits;

   STORE_BUFFER()

   return TRUE;

 }

 /*

  * Emit a restart marker & resynchronize predictions.

  */

 LOCAL(boolean)

 emit_restart (working_state * state, int restart_num)

 {

   int ci;

   if (! flush_bits(state))

     return FALSE;

   emit_byte(state, 0xFF, return FALSE);

   emit_byte(state, JPEG_RST0 + restart_num, return FALSE);

   /* Re-initialize DC predictions to 0 */

   for (ci = 0; ci < state->cinfo->comps_in_scan; ci++)

     state->cur.last_dc_val[ci] = 0;

   /* The restart counter is not updated until we successfully write the MCU. */

   return TRUE;

 }

 /*

  * Encode and output one MCU's worth of Huffman-compressed coefficients.

  */

 METHODDEF(boolean)

 encode_mcu_huff (j_compress_ptr cinfo, JBLOCKROW *MCU_data)

 {

   huff_entropy_ptr entropy = (huff_entropy_ptr) cinfo->entropy;

   working_state state;

   int blkn, ci;

   jpeg_component_info * compptr;

   /* Load up working state */

   state.next_output_byte = cinfo->dest->next_output_byte;

   state.free_in_buffer = cinfo->dest->free_in_buffer;

   ASSIGN_STATE(state.cur, entropy->saved);

   state.cinfo = cinfo;

   /* Emit restart marker if needed */

   if (cinfo->restart_interval) {

     if (entropy->restarts_to_go == 0)

       if (! emit_restart(&state, entropy->next_restart_num))

 	return FALSE;

   }

   /* Encode the MCU data blocks */

   for (blkn = 0; blkn < cinfo->blocks_in_MCU; blkn++) {

     ci = cinfo->MCU_membership[blkn];

     compptr = cinfo->cur_comp_info[ci];

     if (! encode_one_block(&state,

 			   MCU_data[blkn][0], state.cur.last_dc_val[ci],

 			   entropy->dc_derived_tbls[compptr->dc_tbl_no],

 			   entropy->ac_derived_tbls[compptr->ac_tbl_no]))

       return FALSE;

     /* Update last_dc_val */

     state.cur.last_dc_val[ci] = MCU_data[blkn][0][0];

   }

   /* Completed MCU, so update state */

   cinfo->dest->next_output_byte = state.next_output_byte;

   cinfo->dest->free_in_buffer = state.free_in_buffer;

   ASSIGN_STATE(entropy->saved, state.cur);

   /* Update restart-interval state too */

   if (cinfo->restart_interval) {

     if (entropy->restarts_to_go == 0) {

       entropy->restarts_to_go = cinfo->restart_interval;

       entropy->next_restart_num++;

       entropy->next_restart_num &= 7;

     }

     entropy->restarts_to_go--;

   }

   return TRUE;

 }

 /*

  * Finish up at the end of a Huffman-compressed scan.

  */

 METHODDEF(void)

 finish_pass_huff (j_compress_ptr cinfo)

 {

   huff_entropy_ptr entropy = (huff_entropy_ptr) cinfo->entropy;

   working_state state;

   /* Load up working state ... flush_bits needs it */

   state.next_output_byte = cinfo->dest->next_output_byte;

   state.free_in_buffer = cinfo->dest->free_in_buffer;

   ASSIGN_STATE(state.cur, entropy->saved);

   state.cinfo = cinfo;

   /* Flush out the last data */

   if (! flush_bits(&state))

     ERREXIT(cinfo, JERR_CANT_SUSPEND);

   /* Update state */

   cinfo->dest->next_output_byte = state.next_output_byte;

   cinfo->dest->free_in_buffer = state.free_in_buffer;

   ASSIGN_STATE(entropy->saved, state.cur);

 }

 /*

  * Huffman coding optimization.

  *

  * We first scan the supplied data and count the number of uses of each symbol

  * that is to be Huffman-coded. (This process MUST agree with the code above.)

  * Then we build a Huffman coding tree for the observed counts.

  * Symbols which are not needed at all for the particular image are not

  * assigned any code, which saves space in the DHT marker as well as in

  * the compressed data.

  */

 #ifdef ENTROPY_OPT_SUPPORTED

 /* Process a single block's worth of coefficients */

 LOCAL(void)

 htest_one_block (j_compress_ptr cinfo, JCOEFPTR block, int last_dc_val,

 		 long dc_counts[], long ac_counts[])

 {

   register int temp;

   register int nbits;

   register int k, r;

   /* Encode the DC coefficient difference per section F.1.2.1 */

   temp = block[0] - last_dc_val;

   if (temp < 0)

     temp = -temp;

   /* Find the number of bits needed for the magnitude of the coefficient */

   nbits = 0;

   while (temp) {

     nbits++;

     temp >>= 1;

   }

   /* Check for out-of-range coefficient values.

    * Since we're encoding a difference, the range limit is twice as much.

    */

   if (nbits > MAX_COEF_BITS+1)

     ERREXIT(cinfo, JERR_BAD_DCT_COEF);

   /* Count the Huffman symbol for the number of bits */

   dc_counts[nbits]++;

   /* Encode the AC coefficients per section F.1.2.2 */

   r = 0;			/* r = run length of zeros */

   for (k = 1; k < DCTSIZE2; k++) {

     if ((temp = block[jpeg_natural_order[k]]) == 0) {

       r++;

     } else {

       /* if run length > 15, must emit special run-length-16 codes (0xF0) */

       while (r > 15) {

 	ac_counts[0xF0]++;

 	r -= 16;

       }

       /* Find the number of bits needed for the magnitude of the coefficient */

       if (temp < 0)

 	temp = -temp;

       /* Find the number of bits needed for the magnitude of the coefficient */

       nbits = 1;		/* there must be at least one 1 bit */

       while ((temp >>= 1))

 	nbits++;

       /* Check for out-of-range coefficient values */

       if (nbits > MAX_COEF_BITS)

 	ERREXIT(cinfo, JERR_BAD_DCT_COEF);

       /* Count Huffman symbol for run length / number of bits */

       ac_counts[(r << 4) + nbits]++;

       r = 0;

     }

   }

   /* If the last coef(s) were zero, emit an end-of-block code */

   if (r > 0)

     ac_counts[0]++;

 }

 /*

  * Trial-encode one MCU's worth of Huffman-compressed coefficients.

  * No data is actually output, so no suspension return is possible.

  */

 METHODDEF(boolean)

 encode_mcu_gather (j_compress_ptr cinfo, JBLOCKROW *MCU_data)

 {

   huff_entropy_ptr entropy = (huff_entropy_ptr) cinfo->entropy;

   int blkn, ci;

   jpeg_component_info * compptr;

   /* Take care of restart intervals if needed */

   if (cinfo->restart_interval) {

     if (entropy->restarts_to_go == 0) {

       /* Re-initialize DC predictions to 0 */

       for (ci = 0; ci < cinfo->comps_in_scan; ci++)

 	entropy->saved.last_dc_val[ci] = 0;

       /* Update restart state */

       entropy->restarts_to_go = cinfo->restart_interval;

     }

     entropy->restarts_to_go--;

   }

   for (blkn = 0; blkn < cinfo->blocks_in_MCU; blkn++) {

     ci = cinfo->MCU_membership[blkn];

     compptr = cinfo->cur_comp_info[ci];

     htest_one_block(cinfo, MCU_data[blkn][0], entropy->saved.last_dc_val[ci],

 		    entropy->dc_count_ptrs[compptr->dc_tbl_no],

 		    entropy->ac_count_ptrs[compptr->ac_tbl_no]);

     entropy->saved.last_dc_val[ci] = MCU_data[blkn][0][0];

   }

   return TRUE;

 }

 /*

  * Generate the best Huffman code table for the given counts, fill htbl.

  * Note this is also used by jcphuff.c.

  *

  * The JPEG standard requires that no symbol be assigned a codeword of all

  * one bits (so that padding bits added at the end of a compressed segment

  * can't look like a valid code).  Because of the canonical ordering of

  * codewords, this just means that there must be an unused slot in the

  * longest codeword length category.  Section K.2 of the JPEG spec suggests

  * reserving such a slot by pretending that symbol 256 is a valid symbol

  * with count 1.  In theory that's not optimal; giving it count zero but

  * including it in the symbol set anyway should give a better Huffman code.

  * But the theoretically better code actually seems to come out worse in

  * practice, because it produces more all-ones bytes (which incur stuffed

  * zero bytes in the final file).  In any case the difference is tiny.

  *

  * The JPEG standard requires Huffman codes to be no more than 16 bits long.

  * If some symbols have a very small but nonzero probability, the Huffman tree

  * must be adjusted to meet the code length restriction.  We currently use

  * the adjustment method suggested in JPEG section K.2.  This method is *not*

  * optimal; it may not choose the best possible limited-length code.  But

  * typically only very-low-frequency symbols will be given less-than-optimal

  * lengths, so the code is almost optimal.  Experimental comparisons against

  * an optimal limited-length-code algorithm indicate that the difference is

  * microscopic --- usually less than a hundredth of a percent of total size.

  * So the extra complexity of an optimal algorithm doesn't seem worthwhile.

  */

 GLOBAL(void)

 jpeg_gen_optimal_table (j_compress_ptr cinfo, JHUFF_TBL * htbl, long freq[])

 {

 #define MAX_CLEN 32		/* assumed maximum initial code length */

   UINT8 bits[MAX_CLEN+1];	/* bits[k] = # of symbols with code length k */

   int codesize[257];		/* codesize[k] = code length of symbol k */

   int others[257];		/* next symbol in current branch of tree */

   int c1, c2;

   int p, i, j;

   long v;

   /* This algorithm is explained in section K.2 of the JPEG standard */

   MEMZERO(bits, SIZEOF(bits));

   MEMZERO(codesize, SIZEOF(codesize));

   for (i = 0; i < 257; i++)

     others[i] = -1;		/* init links to empty */

   freq[256] = 1;		/* make sure 256 has a nonzero count */

   /* Including the pseudo-symbol 256 in the Huffman procedure guarantees

    * that no real symbol is given code-value of all ones, because 256

    * will be placed last in the largest codeword category.

    */

   /* Huffman's basic algorithm to assign optimal code lengths to symbols */

   for (;;) {

     /* Find the smallest nonzero frequency, set c1 = its symbol */

     /* In case of ties, take the larger symbol number */

     c1 = -1;

     v = 1000000000L;

     for (i = 0; i <= 256; i++) {

       if (freq[i] && freq[i] <= v) {

 	v = freq[i];

 	c1 = i;

       }

     }

     /* Find the next smallest nonzero frequency, set c2 = its symbol */

     /* In case of ties, take the larger symbol number */

     c2 = -1;

     v = 1000000000L;

     for (i = 0; i <= 256; i++) {

       if (freq[i] && freq[i] <= v && i != c1) {

 	v = freq[i];

 	c2 = i;

       }

     }

     /* Done if we've merged everything into one frequency */

     if (c2 < 0)

       break;

     /* Else merge the two counts/trees */

     freq[c1] += freq[c2];

     freq[c2] = 0;

     /* Increment the codesize of everything in c1's tree branch */

     codesize[c1]++;

     while (others[c1] >= 0) {

       c1 = others[c1];

       codesize[c1]++;

     }

     others[c1] = c2;		/* chain c2 onto c1's tree branch */

     /* Increment the codesize of everything in c2's tree branch */

     codesize[c2]++;

     while (others[c2] >= 0) {

       c2 = others[c2];

       codesize[c2]++;

     }

   }

   /* Now count the number of symbols of each code length */

   for (i = 0; i <= 256; i++) {

     if (codesize[i]) {

       /* The JPEG standard seems to think that this can't happen, */

       /* but I'm paranoid... */

       if (codesize[i] > MAX_CLEN)

 	ERREXIT(cinfo, JERR_HUFF_CLEN_OVERFLOW);

       bits[codesize[i]]++;

     }

   }

   /* JPEG doesn't allow symbols with code lengths over 16 bits, so if the pure

    * Huffman procedure assigned any such lengths, we must adjust the coding.

    * Here is what the JPEG spec says about how this next bit works:

    * Since symbols are paired for the longest Huffman code, the symbols are

    * removed from this length category two at a time.  The prefix for the pair

    * (which is one bit shorter) is allocated to one of the pair; then,

    * skipping the BITS entry for that prefix length, a code word from the next

    * shortest nonzero BITS entry is converted into a prefix for two code words

    * one bit longer.

    */

   for (i = MAX_CLEN; i > 16; i--) {

     while (bits[i] > 0) {

       j = i - 2;		/* find length of new prefix to be used */

       while (bits[j] == 0)

 	j--;

       bits[i] -= 2;		/* remove two symbols */

       bits[i-1]++;		/* one goes in this length */

       bits[j+1] += 2;		/* two new symbols in this length */

       bits[j]--;		/* symbol of this length is now a prefix */

     }

   }

   /* Remove the count for the pseudo-symbol 256 from the largest codelength */

   while (bits[i] == 0)		/* find largest codelength still in use */

     i--;

   bits[i]--;

   /* Return final symbol counts (only for lengths 0..16) */

   MEMCOPY(htbl->bits, bits, SIZEOF(htbl->bits));

   /* Return a list of the symbols sorted by code length */

   /* It's not real clear to me why we don't need to consider the codelength

    * changes made above, but the JPEG spec seems to think this works.

    */

   p = 0;

   for (i = 1; i <= MAX_CLEN; i++) {

     for (j = 0; j <= 255; j++) {

       if (codesize[j] == i) {

 	htbl->huffval[p] = (UINT8) j;

 	p++;

       }

     }

   }

   /* Set sent_table FALSE so updated table will be written to JPEG file. */

   htbl->sent_table = FALSE;

 }

 /*

  * Finish up a statistics-gathering pass and create the new Huffman tables.

  */

 METHODDEF(void)

 finish_pass_gather (j_compress_ptr cinfo)

 {

   huff_entropy_ptr entropy = (huff_entropy_ptr) cinfo->entropy;

   int ci, dctbl, actbl;

   jpeg_component_info * compptr;

   JHUFF_TBL **htblptr;

   boolean did_dc[NUM_HUFF_TBLS];

   boolean did_ac[NUM_HUFF_TBLS];

   /* It's important not to apply jpeg_gen_optimal_table more than once

    * per table, because it clobbers the input frequency counts!

    */

   MEMZERO(did_dc, SIZEOF(did_dc));

   MEMZERO(did_ac, SIZEOF(did_ac));

   for (ci = 0; ci < cinfo->comps_in_scan; ci++) {

     compptr = cinfo->cur_comp_info[ci];

     dctbl = compptr->dc_tbl_no;

     actbl = compptr->ac_tbl_no;

     if (! did_dc[dctbl]) {

       htblptr = & cinfo->dc_huff_tbl_ptrs[dctbl];

       if (*htblptr == NULL)

 	*htblptr = jpeg_alloc_huff_table((j_common_ptr) cinfo);

       jpeg_gen_optimal_table(cinfo, *htblptr, entropy->dc_count_ptrs[dctbl]);

       did_dc[dctbl] = TRUE;

     }

     if (! did_ac[actbl]) {

       htblptr = & cinfo->ac_huff_tbl_ptrs[actbl];

       if (*htblptr == NULL)

 	*htblptr = jpeg_alloc_huff_table((j_common_ptr) cinfo);

       jpeg_gen_optimal_table(cinfo, *htblptr, entropy->ac_count_ptrs[actbl]);

       did_ac[actbl] = TRUE;

     }

   }

 }

 #endif /* ENTROPY_OPT_SUPPORTED */

 /*

  * Module initialization routine for Huffman entropy encoding.

  */

 GLOBAL(void)

 jinit_huff_encoder (j_compress_ptr cinfo)

 {

   huff_entropy_ptr entropy;

   int i;

   entropy = (huff_entropy_ptr)

     (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE,

 				SIZEOF(huff_entropy_encoder));

   cinfo->entropy = (struct jpeg_entropy_encoder *) entropy;

   entropy->pub.start_pass = start_pass_huff;

   /* Mark tables unallocated */

   for (i = 0; i < NUM_HUFF_TBLS; i++) {

     entropy->dc_derived_tbls[i] = entropy->ac_derived_tbls[i] = NULL;

 #ifdef ENTROPY_OPT_SUPPORTED

     entropy->dc_count_ptrs[i] = entropy->ac_count_ptrs[i] = NULL;

 #endif

   }

 }