compiler/libjpeg/main/jcshuff.c

   1 /*
   2     $Id$
   3 */
   4
   5 /*
   6  * jcshuff.c
   7  *
   8  * Copyright (C) 1991-1998, Thomas G. Lane.
   9  * This file is part of the Independent JPEG Group's software.
  10  * For conditions of distribution and use, see the accompanying README file.
  11  *
  12  * This file contains Huffman entropy encoding routines for sequential JPEG.
  13  *
  14  * Much of the complexity here has to do with supporting output suspension.
  15  * If the data destination module demands suspension, we want to be able to
  16  * back up to the start of the current MCU.  To do this, we copy state
  17  * variables into local working storage, and update them back to the
  18  * permanent JPEG objects only upon successful completion of an MCU.
  19  */
  20
  21 #define JPEG_INTERNALS
  22 #include "jinclude.h"
  23 #include "jpeglib.h"
  24 #include "jlossy.h"             /* Private declarations for lossy codec */
  25 #include "jchuff.h"             /* Declarations shared with jc*huff.c */
  26
  27
  28 /* Expanded entropy encoder object for Huffman encoding.
  29  *
  30  * The savable_state subrecord contains fields that change within an MCU,
  31  * but must not be updated permanently until we complete the MCU.
  32  */
  33
  34 typedef struct {
  35   INT32 put_buffer;             /* current bit-accumulation buffer */
  36   int put_bits;                 /* # of bits now in it */
  37   int last_dc_val[MAX_COMPS_IN_SCAN]; /* last DC coef for each component */
  38 } savable_state;
  39
  40 /* This macro is to work around compilers with missing or broken
  41  * structure assignment.  You'll need to fix this code if you have
  42  * such a compiler and you change MAX_COMPS_IN_SCAN.
  43  */
  44
  45 #ifndef NO_STRUCT_ASSIGN
  46 #define ASSIGN_STATE(dest,src)  ((dest) = (src))
  47 #else
  48 #if MAX_COMPS_IN_SCAN == 4
  49 #define ASSIGN_STATE(dest,src)  \
  50         ((dest).put_buffer = (src).put_buffer, \
  51          (dest).put_bits = (src).put_bits, \
  52          (dest).last_dc_val[0] = (src).last_dc_val[0], \
  53          (dest).last_dc_val[1] = (src).last_dc_val[1], \
  54          (dest).last_dc_val[2] = (src).last_dc_val[2], \
  55          (dest).last_dc_val[3] = (src).last_dc_val[3])
  56 #endif
  57 #endif
  58
  59
  60 typedef struct {
  61   savable_state saved;          /* Bit buffer & DC state at start of MCU */
  62
  63   /* These fields are NOT loaded into local working state. */
  64   unsigned int restarts_to_go;  /* MCUs left in this restart interval */
  65   int next_restart_num;         /* next restart number to write (0-7) */
  66
  67   /* Pointers to derived tables (these workspaces have image lifespan) */
  68   c_derived_tbl * dc_derived_tbls[NUM_HUFF_TBLS];
  69   c_derived_tbl * ac_derived_tbls[NUM_HUFF_TBLS];
  70
  71 #ifdef ENTROPY_OPT_SUPPORTED    /* Statistics tables for optimization */
  72   long * dc_count_ptrs[NUM_HUFF_TBLS];
  73   long * ac_count_ptrs[NUM_HUFF_TBLS];
  74 #endif
  75 } shuff_entropy_encoder;
  76
  77 typedef shuff_entropy_encoder * shuff_entropy_ptr;
  78
  79 /* Working state while writing an MCU.
  80  * This struct contains all the fields that are needed by subroutines.
  81  */
  82
  83 typedef struct {
  84   JOCTET * next_output_byte;    /* => next byte to write in buffer */
  85   size_t free_in_buffer;        /* # of byte spaces remaining in buffer */
  86   savable_state cur;            /* Current bit buffer & DC state */
  87   j_compress_ptr cinfo;         /* dump_buffer needs access to this */
  88 } working_state;
  89
  90
  91 /* Forward declarations */
  92 METHODDEF(boolean) encode_mcu_huff JPP((j_compress_ptr cinfo,
  93                                         JBLOCKROW *MCU_data));
  94 METHODDEF(void) finish_pass_huff JPP((j_compress_ptr cinfo));
  95 #ifdef ENTROPY_OPT_SUPPORTED
  96 METHODDEF(boolean) encode_mcu_gather JPP((j_compress_ptr cinfo,
  97                                           JBLOCKROW *MCU_data));
  98 METHODDEF(void) finish_pass_gather JPP((j_compress_ptr cinfo));
  99 #endif
 100
 101
 102 /*
 103  * Initialize for a Huffman-compressed scan.
 104  * If gather_statistics is TRUE, we do not output anything during the scan,
 105  * just count the Huffman symbols used and generate Huffman code tables.
 106  */
 107
 108 METHODDEF(void)
 109 start_pass_huff (j_compress_ptr cinfo, boolean gather_statistics)
 110 {
 111   j_lossy_c_ptr lossyc = (j_lossy_c_ptr) cinfo->codec;
 112   shuff_entropy_ptr entropy = (shuff_entropy_ptr) lossyc->entropy_private;
 113   int ci, dctbl, actbl;
 114   jpeg_component_info * compptr;
 115
 116   if (gather_statistics) {
 117 #ifdef ENTROPY_OPT_SUPPORTED
 118     lossyc->entropy_encode_mcu = encode_mcu_gather;
 119     lossyc->pub.entropy_finish_pass = finish_pass_gather;
 120 #else
 121     ERREXIT(cinfo, JERR_NOT_COMPILED);
 122 #endif
 123   } else {
 124     lossyc->entropy_encode_mcu = encode_mcu_huff;
 125     lossyc->pub.entropy_finish_pass = finish_pass_huff;
 126   }
 127
 128   for (ci = 0; ci < cinfo->comps_in_scan; ci++) {
 129     compptr = cinfo->cur_comp_info[ci];
 130     dctbl = compptr->dc_tbl_no;
 131     actbl = compptr->ac_tbl_no;
 132     if (gather_statistics) {
 133 #ifdef ENTROPY_OPT_SUPPORTED
 134       /* Check for invalid table indexes */
 135       /* (make_c_derived_tbl does this in the other path) */
 136       if (dctbl < 0 || dctbl >= NUM_HUFF_TBLS)
 137         ERREXIT1(cinfo, JERR_NO_HUFF_TABLE, dctbl);
 138       if (actbl < 0 || actbl >= NUM_HUFF_TBLS)
 139         ERREXIT1(cinfo, JERR_NO_HUFF_TABLE, actbl);
 140       /* Allocate and zero the statistics tables */
 141       /* Note that jpeg_gen_optimal_table expects 257 entries in each table! */
 142       if (entropy->dc_count_ptrs[dctbl] == NULL)
 143         entropy->dc_count_ptrs[dctbl] = (long *)
 144           (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE,
 145                                       257 * SIZEOF(long));
 146       MEMZERO(entropy->dc_count_ptrs[dctbl], 257 * SIZEOF(long));
 147       if (entropy->ac_count_ptrs[actbl] == NULL)
 148         entropy->ac_count_ptrs[actbl] = (long *)
 149           (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE,
 150                                       257 * SIZEOF(long));
 151       MEMZERO(entropy->ac_count_ptrs[actbl], 257 * SIZEOF(long));
 152 #endif
 153     } else {
 154       /* Compute derived values for Huffman tables */
 155       /* We may do this more than once for a table, but it's not expensive */
 156       jpeg_make_c_derived_tbl(cinfo, TRUE, dctbl,
 157                               & entropy->dc_derived_tbls[dctbl]);
 158       jpeg_make_c_derived_tbl(cinfo, FALSE, actbl,
 159                               & entropy->ac_derived_tbls[actbl]);
 160     }
 161     /* Initialize DC predictions to 0 */
 162     entropy->saved.last_dc_val[ci] = 0;
 163   }
 164
 165   /* Initialize bit buffer to empty */
 166   entropy->saved.put_buffer = 0;
 167   entropy->saved.put_bits = 0;
 168
 169   /* Initialize restart stuff */
 170   entropy->restarts_to_go = cinfo->restart_interval;
 171   entropy->next_restart_num = 0;
 172 }
 173
 174
 175 /* Outputting bytes to the file */
 176
 177 /* Emit a byte, taking 'action' if must suspend. */
 178 #define emit_byte(state,val,action)  \
 179         { *(state)->next_output_byte++ = (JOCTET) (val);  \
 180           if (--(state)->free_in_buffer == 0)  \
 181             if (! dump_buffer(state))  \
 182               { action; } }
 183
 184
 185 LOCAL(boolean)
 186 dump_buffer (working_state * state)
 187 /* Empty the output buffer; return TRUE if successful, FALSE if must suspend */
 188 {
 189   struct jpeg_destination_mgr * dest = state->cinfo->dest;
 190
 191   if (! (*dest->empty_output_buffer) (state->cinfo))
 192     return FALSE;
 193   /* After a successful buffer dump, must reset buffer pointers */
 194   state->next_output_byte = dest->next_output_byte;
 195   state->free_in_buffer = dest->free_in_buffer;
 196   return TRUE;
 197 }
 198
 199
 200 /* Outputting bits to the file */
 201
 202 /* Only the right 24 bits of put_buffer are used; the valid bits are
 203  * left-justified in this part.  At most 16 bits can be passed to emit_bits
 204  * in one call, and we never retain more than 7 bits in put_buffer
 205  * between calls, so 24 bits are sufficient.
 206  */
 207
 208 INLINE
 209 LOCAL(boolean)
 210 emit_bits (working_state * state, unsigned int code, int size)
 211 /* Emit some bits; return TRUE if successful, FALSE if must suspend */
 212 {
 213   /* This routine is heavily used, so it's worth coding tightly. */
 214   register INT32 put_buffer = (INT32) code;
 215   register int put_bits = state->cur.put_bits;
 216
 217   /* if size is 0, caller used an invalid Huffman table entry */
 218   if (size == 0)
 219     ERREXIT(state->cinfo, JERR_HUFF_MISSING_CODE);
 220
 221   put_buffer &= (((INT32) 1)<<size) - 1; /* mask off any extra bits in code */
 222
 223   put_bits += size;             /* new number of bits in buffer */
 224
 225   put_buffer <<= 24 - put_bits; /* align incoming bits */
 226
 227   put_buffer |= state->cur.put_buffer; /* and merge with old buffer contents */
 228
 229   while (put_bits >= 8) {
 230     int c = (int) ((put_buffer >> 16) & 0xFF);
 231
 232     emit_byte(state, c, return FALSE);
 233     if (c == 0xFF) {            /* need to stuff a zero byte? */
 234       emit_byte(state, 0, return FALSE);
 235     }
 236     put_buffer <<= 8;
 237     put_bits -= 8;
 238   }
 239
 240   state->cur.put_buffer = put_buffer; /* update state variables */
 241   state->cur.put_bits = put_bits;
 242
 243   return TRUE;
 244 }
 245
 246
 247 LOCAL(boolean)
 248 flush_bits (working_state * state)
 249 {
 250   if (! emit_bits(state, 0x7F, 7)) /* fill any partial byte with ones */
 251     return FALSE;
 252   state->cur.put_buffer = 0;    /* and reset bit-buffer to empty */
 253   state->cur.put_bits = 0;
 254   return TRUE;
 255 }
 256
 257
 258 /* Encode a single block's worth of coefficients */
 259
 260 LOCAL(boolean)
 261 encode_one_block (working_state * state, JCOEFPTR block, int last_dc_val,
 262                   c_derived_tbl *dctbl, c_derived_tbl *actbl)
 263 {
 264   register int temp, temp2;
 265   register int nbits;
 266   register int k, r, i;
 267
 268   /* Encode the DC coefficient difference per section F.1.2.1 */
 269
 270   temp = temp2 = block[0] - last_dc_val;
 271
 272   if (temp < 0) {
 273     temp = -temp;               /* temp is abs value of input */
 274     /* For a negative input, want temp2 = bitwise complement of abs(input) */
 275     /* This code assumes we are on a two's complement machine */
 276     temp2--;
 277   }
 278
 279   /* Find the number of bits needed for the magnitude of the coefficient */
 280   nbits = 0;
 281   while (temp) {
 282     nbits++;
 283     temp >>= 1;
 284   }
 285   /* Check for out-of-range coefficient values.
 286    * Since we're encoding a difference, the range limit is twice as much.
 287    */
 288   if (nbits > MAX_COEF_BITS+1)
 289     ERREXIT(state->cinfo, JERR_BAD_DCT_COEF);
 290
 291   /* Emit the Huffman-coded symbol for the number of bits */
 292   if (! emit_bits(state, dctbl->ehufco[nbits], dctbl->ehufsi[nbits]))
 293     return FALSE;
 294
 295   /* Emit that number of bits of the value, if positive, */
 296   /* or the complement of its magnitude, if negative. */
 297   if (nbits)                    /* emit_bits rejects calls with size 0 */
 298     if (! emit_bits(state, (unsigned int) temp2, nbits))
 299       return FALSE;
 300
 301   /* Encode the AC coefficients per section F.1.2.2 */
 302
 303   r = 0;                        /* r = run length of zeros */
 304
 305   for (k = 1; k < DCTSIZE2; k++) {
 306     if ((temp = block[jpeg_natural_order[k]]) == 0) {
 307       r++;
 308     } else {
 309       /* if run length > 15, must emit special run-length-16 codes (0xF0) */
 310       while (r > 15) {
 311         if (! emit_bits(state, actbl->ehufco[0xF0], actbl->ehufsi[0xF0]))
 312           return FALSE;
 313         r -= 16;
 314       }
 315
 316       temp2 = temp;
 317       if (temp < 0) {
 318         temp = -temp;           /* temp is abs value of input */
 319         /* This code assumes we are on a two's complement machine */
 320         temp2--;
 321       }
 322
 323       /* Find the number of bits needed for the magnitude of the coefficient */
 324       nbits = 1;                /* there must be at least one 1 bit */
 325       while ((temp >>= 1))
 326         nbits++;
 327       /* Check for out-of-range coefficient values */
 328       if (nbits > MAX_COEF_BITS)
 329         ERREXIT(state->cinfo, JERR_BAD_DCT_COEF);
 330
 331       /* Emit Huffman symbol for run length / number of bits */
 332       i = (r << 4) + nbits;
 333       if (! emit_bits(state, actbl->ehufco[i], actbl->ehufsi[i]))
 334         return FALSE;
 335
 336       /* Emit that number of bits of the value, if positive, */
 337       /* or the complement of its magnitude, if negative. */
 338       if (! emit_bits(state, (unsigned int) temp2, nbits))
 339         return FALSE;
 340
 341       r = 0;
 342     }
 343   }
 344
 345   /* If the last coef(s) were zero, emit an end-of-block code */
 346   if (r > 0)
 347     if (! emit_bits(state, actbl->ehufco[0], actbl->ehufsi[0]))
 348       return FALSE;
 349
 350   return TRUE;
 351 }
 352
 353
 354 /*
 355  * Emit a restart marker & resynchronize predictions.
 356  */
 357
 358 LOCAL(boolean)
 359 emit_restart (working_state * state, int restart_num)
 360 {
 361   int ci;
 362
 363   if (! flush_bits(state))
 364     return FALSE;
 365
 366   emit_byte(state, 0xFF, return FALSE);
 367   emit_byte(state, JPEG_RST0 + restart_num, return FALSE);
 368
 369   /* Re-initialize DC predictions to 0 */
 370   for (ci = 0; ci < state->cinfo->comps_in_scan; ci++)
 371     state->cur.last_dc_val[ci] = 0;
 372
 373   /* The restart counter is not updated until we successfully write the MCU. */
 374
 375   return TRUE;
 376 }
 377
 378
 379 /*
 380  * Encode and output one MCU's worth of Huffman-compressed coefficients.
 381  */
 382
 383 METHODDEF(boolean)
 384 encode_mcu_huff (j_compress_ptr cinfo, JBLOCKROW *MCU_data)
 385 {
 386   j_lossy_c_ptr lossyc = (j_lossy_c_ptr) cinfo->codec;
 387   shuff_entropy_ptr entropy = (shuff_entropy_ptr) lossyc->entropy_private;
 388   working_state state;
 389   int blkn, ci;
 390   jpeg_component_info * compptr;
 391
 392   /* Load up working state */
 393   state.next_output_byte = cinfo->dest->next_output_byte;
 394   state.free_in_buffer = cinfo->dest->free_in_buffer;
 395   ASSIGN_STATE(state.cur, entropy->saved);
 396   state.cinfo = cinfo;
 397
 398   /* Emit restart marker if needed */
 399   if (cinfo->restart_interval) {
 400     if (entropy->restarts_to_go == 0)
 401       if (! emit_restart(&state, entropy->next_restart_num))
 402         return FALSE;
 403   }
 404
 405   /* Encode the MCU data blocks */
 406   for (blkn = 0; blkn < cinfo->data_units_in_MCU; blkn++) {
 407     ci = cinfo->MCU_membership[blkn];
 408     compptr = cinfo->cur_comp_info[ci];
 409     if (! encode_one_block(&state,
 410                            MCU_data[blkn][0], state.cur.last_dc_val[ci],
 411                            entropy->dc_derived_tbls[compptr->dc_tbl_no],
 412                            entropy->ac_derived_tbls[compptr->ac_tbl_no]))
 413       return FALSE;
 414     /* Update last_dc_val */
 415     state.cur.last_dc_val[ci] = MCU_data[blkn][0][0];
 416   }
 417
 418   /* Completed MCU, so update state */
 419   cinfo->dest->next_output_byte = state.next_output_byte;
 420   cinfo->dest->free_in_buffer = state.free_in_buffer;
 421   ASSIGN_STATE(entropy->saved, state.cur);
 422
 423   /* Update restart-interval state too */
 424   if (cinfo->restart_interval) {
 425     if (entropy->restarts_to_go == 0) {
 426       entropy->restarts_to_go = cinfo->restart_interval;
 427       entropy->next_restart_num++;
 428       entropy->next_restart_num &= 7;
 429     }
 430     entropy->restarts_to_go--;
 431   }
 432
 433   return TRUE;
 434 }
 435
 436
 437 /*
 438  * Finish up at the end of a Huffman-compressed scan.
 439  */
 440
 441 METHODDEF(void)
 442 finish_pass_huff (j_compress_ptr cinfo)
 443 {
 444   j_lossy_c_ptr lossyc = (j_lossy_c_ptr) cinfo->codec;
 445   shuff_entropy_ptr entropy = (shuff_entropy_ptr) lossyc->entropy_private;
 446   working_state state;
 447
 448   /* Load up working state ... flush_bits needs it */
 449   state.next_output_byte = cinfo->dest->next_output_byte;
 450   state.free_in_buffer = cinfo->dest->free_in_buffer;
 451   ASSIGN_STATE(state.cur, entropy->saved);
 452   state.cinfo = cinfo;
 453
 454   /* Flush out the last data */
 455   if (! flush_bits(&state))
 456     ERREXIT(cinfo, JERR_CANT_SUSPEND);
 457
 458   /* Update state */
 459   cinfo->dest->next_output_byte = state.next_output_byte;
 460   cinfo->dest->free_in_buffer = state.free_in_buffer;
 461   ASSIGN_STATE(entropy->saved, state.cur);
 462 }
 463
 464
 465 /*
 466  * Huffman coding optimization.
 467  *
 468  * We first scan the supplied data and count the number of uses of each symbol
 469  * that is to be Huffman-coded. (This process MUST agree with the code above.)
 470  * Then we build a Huffman coding tree for the observed counts.
 471  * Symbols which are not needed at all for the particular image are not
 472  * assigned any code, which saves space in the DHT marker as well as in
 473  * the compressed data.
 474  */
 475
 476 #ifdef ENTROPY_OPT_SUPPORTED
 477
 478
 479 /* Process a single block's worth of coefficients */
 480
 481 LOCAL(void)
 482 htest_one_block (j_compress_ptr cinfo, JCOEFPTR block, int last_dc_val,
 483                  long dc_counts[], long ac_counts[])
 484 {
 485   register int temp;
 486   register int nbits;
 487   register int k, r;
 488
 489   /* Encode the DC coefficient difference per section F.1.2.1 */
 490
 491   temp = block[0] - last_dc_val;
 492   if (temp < 0)
 493     temp = -temp;
 494
 495   /* Find the number of bits needed for the magnitude of the coefficient */
 496   nbits = 0;
 497   while (temp) {
 498     nbits++;
 499     temp >>= 1;
 500   }
 501   /* Check for out-of-range coefficient values.
 502    * Since we're encoding a difference, the range limit is twice as much.
 503    */
 504   if (nbits > MAX_COEF_BITS+1)
 505     ERREXIT(cinfo, JERR_BAD_DCT_COEF);
 506
 507   /* Count the Huffman symbol for the number of bits */
 508   dc_counts[nbits]++;
 509
 510   /* Encode the AC coefficients per section F.1.2.2 */
 511
 512   r = 0;                        /* r = run length of zeros */
 513
 514   for (k = 1; k < DCTSIZE2; k++) {
 515     if ((temp = block[jpeg_natural_order[k]]) == 0) {
 516       r++;
 517     } else {
 518       /* if run length > 15, must emit special run-length-16 codes (0xF0) */
 519       while (r > 15) {
 520         ac_counts[0xF0]++;
 521         r -= 16;
 522       }
 523
 524       /* Find the number of bits needed for the magnitude of the coefficient */
 525       if (temp < 0)
 526         temp = -temp;
 527
 528       /* Find the number of bits needed for the magnitude of the coefficient */
 529       nbits = 1;                /* there must be at least one 1 bit */
 530       while ((temp >>= 1))
 531         nbits++;
 532       /* Check for out-of-range coefficient values */
 533       if (nbits > MAX_COEF_BITS)
 534         ERREXIT(cinfo, JERR_BAD_DCT_COEF);
 535
 536       /* Count Huffman symbol for run length / number of bits */
 537       ac_counts[(r << 4) + nbits]++;
 538
 539       r = 0;
 540     }
 541   }
 542
 543   /* If the last coef(s) were zero, emit an end-of-block code */
 544   if (r > 0)
 545     ac_counts[0]++;
 546 }
 547
 548
 549 /*
 550  * Trial-encode one MCU's worth of Huffman-compressed coefficients.
 551  * No data is actually output, so no suspension return is possible.
 552  */
 553
 554 METHODDEF(boolean)
 555 encode_mcu_gather (j_compress_ptr cinfo, JBLOCKROW *MCU_data)
 556 {
 557   j_lossy_c_ptr lossyc = (j_lossy_c_ptr) cinfo->codec;
 558   shuff_entropy_ptr entropy = (shuff_entropy_ptr) lossyc->entropy_private;
 559   int blkn, ci;
 560   jpeg_component_info * compptr;
 561
 562   /* Take care of restart intervals if needed */
 563   if (cinfo->restart_interval) {
 564     if (entropy->restarts_to_go == 0) {
 565       /* Re-initialize DC predictions to 0 */
 566       for (ci = 0; ci < cinfo->comps_in_scan; ci++)
 567         entropy->saved.last_dc_val[ci] = 0;
 568       /* Update restart state */
 569       entropy->restarts_to_go = cinfo->restart_interval;
 570     }
 571     entropy->restarts_to_go--;
 572   }
 573
 574   for (blkn = 0; blkn < cinfo->data_units_in_MCU; blkn++) {
 575     ci = cinfo->MCU_membership[blkn];
 576     compptr = cinfo->cur_comp_info[ci];
 577     htest_one_block(cinfo, MCU_data[blkn][0], entropy->saved.last_dc_val[ci],
 578                     entropy->dc_count_ptrs[compptr->dc_tbl_no],
 579                     entropy->ac_count_ptrs[compptr->ac_tbl_no]);
 580     entropy->saved.last_dc_val[ci] = MCU_data[blkn][0][0];
 581   }
 582
 583   return TRUE;
 584 }
 585
 586
 587 /*
 588  * Finish up a statistics-gathering pass and create the new Huffman tables.
 589  */
 590
 591 METHODDEF(void)
 592 finish_pass_gather (j_compress_ptr cinfo)
 593 {
 594   j_lossy_c_ptr lossyc = (j_lossy_c_ptr) cinfo->codec;
 595   shuff_entropy_ptr entropy = (shuff_entropy_ptr) lossyc->entropy_private;
 596   int ci, dctbl, actbl;
 597   jpeg_component_info * compptr;
 598   JHUFF_TBL **htblptr;
 599   boolean did_dc[NUM_HUFF_TBLS];
 600   boolean did_ac[NUM_HUFF_TBLS];
 601
 602   /* It's important not to apply jpeg_gen_optimal_table more than once
 603    * per table, because it clobbers the input frequency counts!
 604    */
 605   MEMZERO(did_dc, SIZEOF(did_dc));
 606   MEMZERO(did_ac, SIZEOF(did_ac));
 607
 608   for (ci = 0; ci < cinfo->comps_in_scan; ci++) {
 609     compptr = cinfo->cur_comp_info[ci];
 610     dctbl = compptr->dc_tbl_no;
 611     actbl = compptr->ac_tbl_no;
 612     if (! did_dc[dctbl]) {
 613       htblptr = & cinfo->dc_huff_tbl_ptrs[dctbl];
 614       if (*htblptr == NULL)
 615         *htblptr = jpeg_alloc_huff_table((j_common_ptr) cinfo);
 616       jpeg_gen_optimal_table(cinfo, *htblptr, entropy->dc_count_ptrs[dctbl]);
 617       did_dc[dctbl] = TRUE;
 618     }
 619     if (! did_ac[actbl]) {
 620       htblptr = & cinfo->ac_huff_tbl_ptrs[actbl];
 621       if (*htblptr == NULL)
 622         *htblptr = jpeg_alloc_huff_table((j_common_ptr) cinfo);
 623       jpeg_gen_optimal_table(cinfo, *htblptr, entropy->ac_count_ptrs[actbl]);
 624       did_ac[actbl] = TRUE;
 625     }
 626   }
 627 }
 628
 629
 630 #endif /* ENTROPY_OPT_SUPPORTED */
 631
 632
 633 METHODDEF(boolean)
 634 need_optimization_pass (j_compress_ptr cinfo)
 635 {
 636   return TRUE;
 637 }
 638
 639
 640 /*
 641  * Module initialization routine for Huffman entropy encoding.
 642  */
 643
 644 JGLOBAL(void)
 645 jinit_shuff_encoder (j_compress_ptr cinfo)
 646 {
 647   j_lossy_c_ptr lossyc = (j_lossy_c_ptr) cinfo->codec;
 648   shuff_entropy_ptr entropy;
 649   int i;
 650
 651   entropy = (shuff_entropy_ptr)
 652     (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE,
 653                                 SIZEOF(shuff_entropy_encoder));
 654   lossyc->entropy_private = (struct jpeg_entropy_encoder *) entropy;
 655   lossyc->pub.entropy_start_pass = start_pass_huff;
 656   lossyc->pub.need_optimization_pass = need_optimization_pass;
 657
 658   /* Mark tables unallocated */
 659   for (i = 0; i < NUM_HUFF_TBLS; i++) {
 660     entropy->dc_derived_tbls[i] = entropy->ac_derived_tbls[i] = NULL;
 661 #ifdef ENTROPY_OPT_SUPPORTED
 662     entropy->dc_count_ptrs[i] = entropy->ac_count_ptrs[i] = NULL;
 663 #endif
 664   }
 665 }