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/src/FreeImage/Source/LibJPEG/jchuff.c

https://bitbucket.org/cabalistic/ogredeps/
C | 1576 lines | 928 code | 279 blank | 369 comment | 236 complexity | 019b6da0b5f264fc84337a1721a4f3c9 MD5 | raw file
   1/*
   2 * jchuff.c
   3 *
   4 * Copyright (C) 1991-1997, Thomas G. Lane.
   5 * Modified 2006-2009 by Guido Vollbeding.
   6 * This file is part of the Independent JPEG Group's software.
   7 * For conditions of distribution and use, see the accompanying README file.
   8 *
   9 * This file contains Huffman entropy encoding routines.
  10 * Both sequential and progressive modes are supported in this single module.
  11 *
  12 * Much of the complexity here has to do with supporting output suspension.
  13 * If the data destination module demands suspension, we want to be able to
  14 * back up to the start of the current MCU.  To do this, we copy state
  15 * variables into local working storage, and update them back to the
  16 * permanent JPEG objects only upon successful completion of an MCU.
  17 *
  18 * We do not support output suspension for the progressive JPEG mode, since
  19 * the library currently does not allow multiple-scan files to be written
  20 * with output suspension.
  21 */
  22
  23#define JPEG_INTERNALS
  24#include "jinclude.h"
  25#include "jpeglib.h"
  26
  27
  28/* The legal range of a DCT coefficient is
  29 *  -1024 .. +1023  for 8-bit data;
  30 * -16384 .. +16383 for 12-bit data.
  31 * Hence the magnitude should always fit in 10 or 14 bits respectively.
  32 */
  33
  34#if BITS_IN_JSAMPLE == 8
  35#define MAX_COEF_BITS 10
  36#else
  37#define MAX_COEF_BITS 14
  38#endif
  39
  40/* Derived data constructed for each Huffman table */
  41
  42typedef struct {
  43  unsigned int ehufco[256];	/* code for each symbol */
  44  char ehufsi[256];		/* length of code for each symbol */
  45  /* If no code has been allocated for a symbol S, ehufsi[S] contains 0 */
  46} c_derived_tbl;
  47
  48
  49/* Expanded entropy encoder object for Huffman encoding.
  50 *
  51 * The savable_state subrecord contains fields that change within an MCU,
  52 * but must not be updated permanently until we complete the MCU.
  53 */
  54
  55typedef struct {
  56  INT32 put_buffer;		/* current bit-accumulation buffer */
  57  int put_bits;			/* # of bits now in it */
  58  int last_dc_val[MAX_COMPS_IN_SCAN]; /* last DC coef for each component */
  59} savable_state;
  60
  61/* This macro is to work around compilers with missing or broken
  62 * structure assignment.  You'll need to fix this code if you have
  63 * such a compiler and you change MAX_COMPS_IN_SCAN.
  64 */
  65
  66#ifndef NO_STRUCT_ASSIGN
  67#define ASSIGN_STATE(dest,src)  ((dest) = (src))
  68#else
  69#if MAX_COMPS_IN_SCAN == 4
  70#define ASSIGN_STATE(dest,src)  \
  71	((dest).put_buffer = (src).put_buffer, \
  72	 (dest).put_bits = (src).put_bits, \
  73	 (dest).last_dc_val[0] = (src).last_dc_val[0], \
  74	 (dest).last_dc_val[1] = (src).last_dc_val[1], \
  75	 (dest).last_dc_val[2] = (src).last_dc_val[2], \
  76	 (dest).last_dc_val[3] = (src).last_dc_val[3])
  77#endif
  78#endif
  79
  80
  81typedef struct {
  82  struct jpeg_entropy_encoder pub; /* public fields */
  83
  84  savable_state saved;		/* Bit buffer & DC state at start of MCU */
  85
  86  /* These fields are NOT loaded into local working state. */
  87  unsigned int restarts_to_go;	/* MCUs left in this restart interval */
  88  int next_restart_num;		/* next restart number to write (0-7) */
  89
  90  /* Pointers to derived tables (these workspaces have image lifespan) */
  91  c_derived_tbl * dc_derived_tbls[NUM_HUFF_TBLS];
  92  c_derived_tbl * ac_derived_tbls[NUM_HUFF_TBLS];
  93
  94  /* Statistics tables for optimization */
  95  long * dc_count_ptrs[NUM_HUFF_TBLS];
  96  long * ac_count_ptrs[NUM_HUFF_TBLS];
  97
  98  /* Following fields used only in progressive mode */
  99
 100  /* Mode flag: TRUE for optimization, FALSE for actual data output */
 101  boolean gather_statistics;
 102
 103  /* next_output_byte/free_in_buffer are local copies of cinfo->dest fields.
 104   */
 105  JOCTET * next_output_byte;	/* => next byte to write in buffer */
 106  size_t free_in_buffer;	/* # of byte spaces remaining in buffer */
 107  j_compress_ptr cinfo;		/* link to cinfo (needed for dump_buffer) */
 108
 109  /* Coding status for AC components */
 110  int ac_tbl_no;		/* the table number of the single component */
 111  unsigned int EOBRUN;		/* run length of EOBs */
 112  unsigned int BE;		/* # of buffered correction bits before MCU */
 113  char * bit_buffer;		/* buffer for correction bits (1 per char) */
 114  /* packing correction bits tightly would save some space but cost time... */
 115} huff_entropy_encoder;
 116
 117typedef huff_entropy_encoder * huff_entropy_ptr;
 118
 119/* Working state while writing an MCU (sequential mode).
 120 * This struct contains all the fields that are needed by subroutines.
 121 */
 122
 123typedef struct {
 124  JOCTET * next_output_byte;	/* => next byte to write in buffer */
 125  size_t free_in_buffer;	/* # of byte spaces remaining in buffer */
 126  savable_state cur;		/* Current bit buffer & DC state */
 127  j_compress_ptr cinfo;		/* dump_buffer needs access to this */
 128} working_state;
 129
 130/* MAX_CORR_BITS is the number of bits the AC refinement correction-bit
 131 * buffer can hold.  Larger sizes may slightly improve compression, but
 132 * 1000 is already well into the realm of overkill.
 133 * The minimum safe size is 64 bits.
 134 */
 135
 136#define MAX_CORR_BITS  1000	/* Max # of correction bits I can buffer */
 137
 138/* IRIGHT_SHIFT is like RIGHT_SHIFT, but works on int rather than INT32.
 139 * We assume that int right shift is unsigned if INT32 right shift is,
 140 * which should be safe.
 141 */
 142
 143#ifdef RIGHT_SHIFT_IS_UNSIGNED
 144#define ISHIFT_TEMPS	int ishift_temp;
 145#define IRIGHT_SHIFT(x,shft)  \
 146	((ishift_temp = (x)) < 0 ? \
 147	 (ishift_temp >> (shft)) | ((~0) << (16-(shft))) : \
 148	 (ishift_temp >> (shft)))
 149#else
 150#define ISHIFT_TEMPS
 151#define IRIGHT_SHIFT(x,shft)	((x) >> (shft))
 152#endif
 153
 154
 155/*
 156 * Compute the derived values for a Huffman table.
 157 * This routine also performs some validation checks on the table.
 158 */
 159
 160LOCAL(void)
 161jpeg_make_c_derived_tbl (j_compress_ptr cinfo, boolean isDC, int tblno,
 162			 c_derived_tbl ** pdtbl)
 163{
 164  JHUFF_TBL *htbl;
 165  c_derived_tbl *dtbl;
 166  int p, i, l, lastp, si, maxsymbol;
 167  char huffsize[257];
 168  unsigned int huffcode[257];
 169  unsigned int code;
 170
 171  /* Note that huffsize[] and huffcode[] are filled in code-length order,
 172   * paralleling the order of the symbols themselves in htbl->huffval[].
 173   */
 174
 175  /* Find the input Huffman table */
 176  if (tblno < 0 || tblno >= NUM_HUFF_TBLS)
 177    ERREXIT1(cinfo, JERR_NO_HUFF_TABLE, tblno);
 178  htbl =
 179    isDC ? cinfo->dc_huff_tbl_ptrs[tblno] : cinfo->ac_huff_tbl_ptrs[tblno];
 180  if (htbl == NULL)
 181    ERREXIT1(cinfo, JERR_NO_HUFF_TABLE, tblno);
 182
 183  /* Allocate a workspace if we haven't already done so. */
 184  if (*pdtbl == NULL)
 185    *pdtbl = (c_derived_tbl *)
 186      (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE,
 187				  SIZEOF(c_derived_tbl));
 188  dtbl = *pdtbl;
 189  
 190  /* Figure C.1: make table of Huffman code length for each symbol */
 191
 192  p = 0;
 193  for (l = 1; l <= 16; l++) {
 194    i = (int) htbl->bits[l];
 195    if (i < 0 || p + i > 256)	/* protect against table overrun */
 196      ERREXIT(cinfo, JERR_BAD_HUFF_TABLE);
 197    while (i--)
 198      huffsize[p++] = (char) l;
 199  }
 200  huffsize[p] = 0;
 201  lastp = p;
 202  
 203  /* Figure C.2: generate the codes themselves */
 204  /* We also validate that the counts represent a legal Huffman code tree. */
 205
 206  code = 0;
 207  si = huffsize[0];
 208  p = 0;
 209  while (huffsize[p]) {
 210    while (((int) huffsize[p]) == si) {
 211      huffcode[p++] = code;
 212      code++;
 213    }
 214    /* code is now 1 more than the last code used for codelength si; but
 215     * it must still fit in si bits, since no code is allowed to be all ones.
 216     */
 217    if (((INT32) code) >= (((INT32) 1) << si))
 218      ERREXIT(cinfo, JERR_BAD_HUFF_TABLE);
 219    code <<= 1;
 220    si++;
 221  }
 222  
 223  /* Figure C.3: generate encoding tables */
 224  /* These are code and size indexed by symbol value */
 225
 226  /* Set all codeless symbols to have code length 0;
 227   * this lets us detect duplicate VAL entries here, and later
 228   * allows emit_bits to detect any attempt to emit such symbols.
 229   */
 230  MEMZERO(dtbl->ehufsi, SIZEOF(dtbl->ehufsi));
 231
 232  /* This is also a convenient place to check for out-of-range
 233   * and duplicated VAL entries.  We allow 0..255 for AC symbols
 234   * but only 0..15 for DC.  (We could constrain them further
 235   * based on data depth and mode, but this seems enough.)
 236   */
 237  maxsymbol = isDC ? 15 : 255;
 238
 239  for (p = 0; p < lastp; p++) {
 240    i = htbl->huffval[p];
 241    if (i < 0 || i > maxsymbol || dtbl->ehufsi[i])
 242      ERREXIT(cinfo, JERR_BAD_HUFF_TABLE);
 243    dtbl->ehufco[i] = huffcode[p];
 244    dtbl->ehufsi[i] = huffsize[p];
 245  }
 246}
 247
 248
 249/* Outputting bytes to the file.
 250 * NB: these must be called only when actually outputting,
 251 * that is, entropy->gather_statistics == FALSE.
 252 */
 253
 254/* Emit a byte, taking 'action' if must suspend. */
 255#define emit_byte_s(state,val,action)  \
 256	{ *(state)->next_output_byte++ = (JOCTET) (val);  \
 257	  if (--(state)->free_in_buffer == 0)  \
 258	    if (! dump_buffer_s(state))  \
 259	      { action; } }
 260
 261/* Emit a byte */
 262#define emit_byte_e(entropy,val)  \
 263	{ *(entropy)->next_output_byte++ = (JOCTET) (val);  \
 264	  if (--(entropy)->free_in_buffer == 0)  \
 265	    dump_buffer_e(entropy); }
 266
 267
 268LOCAL(boolean)
 269dump_buffer_s (working_state * state)
 270/* Empty the output buffer; return TRUE if successful, FALSE if must suspend */
 271{
 272  struct jpeg_destination_mgr * dest = state->cinfo->dest;
 273
 274  if (! (*dest->empty_output_buffer) (state->cinfo))
 275    return FALSE;
 276  /* After a successful buffer dump, must reset buffer pointers */
 277  state->next_output_byte = dest->next_output_byte;
 278  state->free_in_buffer = dest->free_in_buffer;
 279  return TRUE;
 280}
 281
 282
 283LOCAL(void)
 284dump_buffer_e (huff_entropy_ptr entropy)
 285/* Empty the output buffer; we do not support suspension in this case. */
 286{
 287  struct jpeg_destination_mgr * dest = entropy->cinfo->dest;
 288
 289  if (! (*dest->empty_output_buffer) (entropy->cinfo))
 290    ERREXIT(entropy->cinfo, JERR_CANT_SUSPEND);
 291  /* After a successful buffer dump, must reset buffer pointers */
 292  entropy->next_output_byte = dest->next_output_byte;
 293  entropy->free_in_buffer = dest->free_in_buffer;
 294}
 295
 296
 297/* Outputting bits to the file */
 298
 299/* Only the right 24 bits of put_buffer are used; the valid bits are
 300 * left-justified in this part.  At most 16 bits can be passed to emit_bits
 301 * in one call, and we never retain more than 7 bits in put_buffer
 302 * between calls, so 24 bits are sufficient.
 303 */
 304
 305INLINE
 306LOCAL(boolean)
 307emit_bits_s (working_state * state, unsigned int code, int size)
 308/* Emit some bits; return TRUE if successful, FALSE if must suspend */
 309{
 310  /* This routine is heavily used, so it's worth coding tightly. */
 311  register INT32 put_buffer = (INT32) code;
 312  register int put_bits = state->cur.put_bits;
 313
 314  /* if size is 0, caller used an invalid Huffman table entry */
 315  if (size == 0)
 316    ERREXIT(state->cinfo, JERR_HUFF_MISSING_CODE);
 317
 318  put_buffer &= (((INT32) 1)<<size) - 1; /* mask off any extra bits in code */
 319  
 320  put_bits += size;		/* new number of bits in buffer */
 321  
 322  put_buffer <<= 24 - put_bits; /* align incoming bits */
 323
 324  put_buffer |= state->cur.put_buffer; /* and merge with old buffer contents */
 325  
 326  while (put_bits >= 8) {
 327    int c = (int) ((put_buffer >> 16) & 0xFF);
 328    
 329    emit_byte_s(state, c, return FALSE);
 330    if (c == 0xFF) {		/* need to stuff a zero byte? */
 331      emit_byte_s(state, 0, return FALSE);
 332    }
 333    put_buffer <<= 8;
 334    put_bits -= 8;
 335  }
 336
 337  state->cur.put_buffer = put_buffer; /* update state variables */
 338  state->cur.put_bits = put_bits;
 339
 340  return TRUE;
 341}
 342
 343
 344INLINE
 345LOCAL(void)
 346emit_bits_e (huff_entropy_ptr entropy, unsigned int code, int size)
 347/* Emit some bits, unless we are in gather mode */
 348{
 349  /* This routine is heavily used, so it's worth coding tightly. */
 350  register INT32 put_buffer = (INT32) code;
 351  register int put_bits = entropy->saved.put_bits;
 352
 353  /* if size is 0, caller used an invalid Huffman table entry */
 354  if (size == 0)
 355    ERREXIT(entropy->cinfo, JERR_HUFF_MISSING_CODE);
 356
 357  if (entropy->gather_statistics)
 358    return;			/* do nothing if we're only getting stats */
 359
 360  put_buffer &= (((INT32) 1)<<size) - 1; /* mask off any extra bits in code */
 361  
 362  put_bits += size;		/* new number of bits in buffer */
 363
 364  put_buffer <<= 24 - put_bits; /* align incoming bits */
 365
 366  /* and merge with old buffer contents */
 367  put_buffer |= entropy->saved.put_buffer;
 368
 369  while (put_bits >= 8) {
 370    int c = (int) ((put_buffer >> 16) & 0xFF);
 371
 372    emit_byte_e(entropy, c);
 373    if (c == 0xFF) {		/* need to stuff a zero byte? */
 374      emit_byte_e(entropy, 0);
 375    }
 376    put_buffer <<= 8;
 377    put_bits -= 8;
 378  }
 379
 380  entropy->saved.put_buffer = put_buffer; /* update variables */
 381  entropy->saved.put_bits = put_bits;
 382}
 383
 384
 385LOCAL(boolean)
 386flush_bits_s (working_state * state)
 387{
 388  if (! emit_bits_s(state, 0x7F, 7)) /* fill any partial byte with ones */
 389    return FALSE;
 390  state->cur.put_buffer = 0;	     /* and reset bit-buffer to empty */
 391  state->cur.put_bits = 0;
 392  return TRUE;
 393}
 394
 395
 396LOCAL(void)
 397flush_bits_e (huff_entropy_ptr entropy)
 398{
 399  emit_bits_e(entropy, 0x7F, 7); /* fill any partial byte with ones */
 400  entropy->saved.put_buffer = 0; /* and reset bit-buffer to empty */
 401  entropy->saved.put_bits = 0;
 402}
 403
 404
 405/*
 406 * Emit (or just count) a Huffman symbol.
 407 */
 408
 409INLINE
 410LOCAL(void)
 411emit_dc_symbol (huff_entropy_ptr entropy, int tbl_no, int symbol)
 412{
 413  if (entropy->gather_statistics)
 414    entropy->dc_count_ptrs[tbl_no][symbol]++;
 415  else {
 416    c_derived_tbl * tbl = entropy->dc_derived_tbls[tbl_no];
 417    emit_bits_e(entropy, tbl->ehufco[symbol], tbl->ehufsi[symbol]);
 418  }
 419}
 420
 421
 422INLINE
 423LOCAL(void)
 424emit_ac_symbol (huff_entropy_ptr entropy, int tbl_no, int symbol)
 425{
 426  if (entropy->gather_statistics)
 427    entropy->ac_count_ptrs[tbl_no][symbol]++;
 428  else {
 429    c_derived_tbl * tbl = entropy->ac_derived_tbls[tbl_no];
 430    emit_bits_e(entropy, tbl->ehufco[symbol], tbl->ehufsi[symbol]);
 431  }
 432}
 433
 434
 435/*
 436 * Emit bits from a correction bit buffer.
 437 */
 438
 439LOCAL(void)
 440emit_buffered_bits (huff_entropy_ptr entropy, char * bufstart,
 441		    unsigned int nbits)
 442{
 443  if (entropy->gather_statistics)
 444    return;			/* no real work */
 445
 446  while (nbits > 0) {
 447    emit_bits_e(entropy, (unsigned int) (*bufstart), 1);
 448    bufstart++;
 449    nbits--;
 450  }
 451}
 452
 453
 454/*
 455 * Emit any pending EOBRUN symbol.
 456 */
 457
 458LOCAL(void)
 459emit_eobrun (huff_entropy_ptr entropy)
 460{
 461  register int temp, nbits;
 462
 463  if (entropy->EOBRUN > 0) {	/* if there is any pending EOBRUN */
 464    temp = entropy->EOBRUN;
 465    nbits = 0;
 466    while ((temp >>= 1))
 467      nbits++;
 468    /* safety check: shouldn't happen given limited correction-bit buffer */
 469    if (nbits > 14)
 470      ERREXIT(entropy->cinfo, JERR_HUFF_MISSING_CODE);
 471
 472    emit_ac_symbol(entropy, entropy->ac_tbl_no, nbits << 4);
 473    if (nbits)
 474      emit_bits_e(entropy, entropy->EOBRUN, nbits);
 475
 476    entropy->EOBRUN = 0;
 477
 478    /* Emit any buffered correction bits */
 479    emit_buffered_bits(entropy, entropy->bit_buffer, entropy->BE);
 480    entropy->BE = 0;
 481  }
 482}
 483
 484
 485/*
 486 * Emit a restart marker & resynchronize predictions.
 487 */
 488
 489LOCAL(boolean)
 490emit_restart_s (working_state * state, int restart_num)
 491{
 492  int ci;
 493
 494  if (! flush_bits_s(state))
 495    return FALSE;
 496
 497  emit_byte_s(state, 0xFF, return FALSE);
 498  emit_byte_s(state, JPEG_RST0 + restart_num, return FALSE);
 499
 500  /* Re-initialize DC predictions to 0 */
 501  for (ci = 0; ci < state->cinfo->comps_in_scan; ci++)
 502    state->cur.last_dc_val[ci] = 0;
 503
 504  /* The restart counter is not updated until we successfully write the MCU. */
 505
 506  return TRUE;
 507}
 508
 509
 510LOCAL(void)
 511emit_restart_e (huff_entropy_ptr entropy, int restart_num)
 512{
 513  int ci;
 514
 515  emit_eobrun(entropy);
 516
 517  if (! entropy->gather_statistics) {
 518    flush_bits_e(entropy);
 519    emit_byte_e(entropy, 0xFF);
 520    emit_byte_e(entropy, JPEG_RST0 + restart_num);
 521  }
 522
 523  if (entropy->cinfo->Ss == 0) {
 524    /* Re-initialize DC predictions to 0 */
 525    for (ci = 0; ci < entropy->cinfo->comps_in_scan; ci++)
 526      entropy->saved.last_dc_val[ci] = 0;
 527  } else {
 528    /* Re-initialize all AC-related fields to 0 */
 529    entropy->EOBRUN = 0;
 530    entropy->BE = 0;
 531  }
 532}
 533
 534
 535/*
 536 * MCU encoding for DC initial scan (either spectral selection,
 537 * or first pass of successive approximation).
 538 */
 539
 540METHODDEF(boolean)
 541encode_mcu_DC_first (j_compress_ptr cinfo, JBLOCKROW *MCU_data)
 542{
 543  huff_entropy_ptr entropy = (huff_entropy_ptr) cinfo->entropy;
 544  register int temp, temp2;
 545  register int nbits;
 546  int blkn, ci;
 547  int Al = cinfo->Al;
 548  JBLOCKROW block;
 549  jpeg_component_info * compptr;
 550  ISHIFT_TEMPS
 551
 552  entropy->next_output_byte = cinfo->dest->next_output_byte;
 553  entropy->free_in_buffer = cinfo->dest->free_in_buffer;
 554
 555  /* Emit restart marker if needed */
 556  if (cinfo->restart_interval)
 557    if (entropy->restarts_to_go == 0)
 558      emit_restart_e(entropy, entropy->next_restart_num);
 559
 560  /* Encode the MCU data blocks */
 561  for (blkn = 0; blkn < cinfo->blocks_in_MCU; blkn++) {
 562    block = MCU_data[blkn];
 563    ci = cinfo->MCU_membership[blkn];
 564    compptr = cinfo->cur_comp_info[ci];
 565
 566    /* Compute the DC value after the required point transform by Al.
 567     * This is simply an arithmetic right shift.
 568     */
 569    temp2 = IRIGHT_SHIFT((int) ((*block)[0]), Al);
 570
 571    /* DC differences are figured on the point-transformed values. */
 572    temp = temp2 - entropy->saved.last_dc_val[ci];
 573    entropy->saved.last_dc_val[ci] = temp2;
 574
 575    /* Encode the DC coefficient difference per section G.1.2.1 */
 576    temp2 = temp;
 577    if (temp < 0) {
 578      temp = -temp;		/* temp is abs value of input */
 579      /* For a negative input, want temp2 = bitwise complement of abs(input) */
 580      /* This code assumes we are on a two's complement machine */
 581      temp2--;
 582    }
 583    
 584    /* Find the number of bits needed for the magnitude of the coefficient */
 585    nbits = 0;
 586    while (temp) {
 587      nbits++;
 588      temp >>= 1;
 589    }
 590    /* Check for out-of-range coefficient values.
 591     * Since we're encoding a difference, the range limit is twice as much.
 592     */
 593    if (nbits > MAX_COEF_BITS+1)
 594      ERREXIT(cinfo, JERR_BAD_DCT_COEF);
 595    
 596    /* Count/emit the Huffman-coded symbol for the number of bits */
 597    emit_dc_symbol(entropy, compptr->dc_tbl_no, nbits);
 598    
 599    /* Emit that number of bits of the value, if positive, */
 600    /* or the complement of its magnitude, if negative. */
 601    if (nbits)			/* emit_bits rejects calls with size 0 */
 602      emit_bits_e(entropy, (unsigned int) temp2, nbits);
 603  }
 604
 605  cinfo->dest->next_output_byte = entropy->next_output_byte;
 606  cinfo->dest->free_in_buffer = entropy->free_in_buffer;
 607
 608  /* Update restart-interval state too */
 609  if (cinfo->restart_interval) {
 610    if (entropy->restarts_to_go == 0) {
 611      entropy->restarts_to_go = cinfo->restart_interval;
 612      entropy->next_restart_num++;
 613      entropy->next_restart_num &= 7;
 614    }
 615    entropy->restarts_to_go--;
 616  }
 617
 618  return TRUE;
 619}
 620
 621
 622/*
 623 * MCU encoding for AC initial scan (either spectral selection,
 624 * or first pass of successive approximation).
 625 */
 626
 627METHODDEF(boolean)
 628encode_mcu_AC_first (j_compress_ptr cinfo, JBLOCKROW *MCU_data)
 629{
 630  huff_entropy_ptr entropy = (huff_entropy_ptr) cinfo->entropy;
 631  register int temp, temp2;
 632  register int nbits;
 633  register int r, k;
 634  int Se, Al;
 635  const int * natural_order;
 636  JBLOCKROW block;
 637
 638  entropy->next_output_byte = cinfo->dest->next_output_byte;
 639  entropy->free_in_buffer = cinfo->dest->free_in_buffer;
 640
 641  /* Emit restart marker if needed */
 642  if (cinfo->restart_interval)
 643    if (entropy->restarts_to_go == 0)
 644      emit_restart_e(entropy, entropy->next_restart_num);
 645
 646  Se = cinfo->Se;
 647  Al = cinfo->Al;
 648  natural_order = cinfo->natural_order;
 649
 650  /* Encode the MCU data block */
 651  block = MCU_data[0];
 652
 653  /* Encode the AC coefficients per section G.1.2.2, fig. G.3 */
 654  
 655  r = 0;			/* r = run length of zeros */
 656   
 657  for (k = cinfo->Ss; k <= Se; k++) {
 658    if ((temp = (*block)[natural_order[k]]) == 0) {
 659      r++;
 660      continue;
 661    }
 662    /* We must apply the point transform by Al.  For AC coefficients this
 663     * is an integer division with rounding towards 0.  To do this portably
 664     * in C, we shift after obtaining the absolute value; so the code is
 665     * interwoven with finding the abs value (temp) and output bits (temp2).
 666     */
 667    if (temp < 0) {
 668      temp = -temp;		/* temp is abs value of input */
 669      temp >>= Al;		/* apply the point transform */
 670      /* For a negative coef, want temp2 = bitwise complement of abs(coef) */
 671      temp2 = ~temp;
 672    } else {
 673      temp >>= Al;		/* apply the point transform */
 674      temp2 = temp;
 675    }
 676    /* Watch out for case that nonzero coef is zero after point transform */
 677    if (temp == 0) {
 678      r++;
 679      continue;
 680    }
 681
 682    /* Emit any pending EOBRUN */
 683    if (entropy->EOBRUN > 0)
 684      emit_eobrun(entropy);
 685    /* if run length > 15, must emit special run-length-16 codes (0xF0) */
 686    while (r > 15) {
 687      emit_ac_symbol(entropy, entropy->ac_tbl_no, 0xF0);
 688      r -= 16;
 689    }
 690
 691    /* Find the number of bits needed for the magnitude of the coefficient */
 692    nbits = 1;			/* there must be at least one 1 bit */
 693    while ((temp >>= 1))
 694      nbits++;
 695    /* Check for out-of-range coefficient values */
 696    if (nbits > MAX_COEF_BITS)
 697      ERREXIT(cinfo, JERR_BAD_DCT_COEF);
 698
 699    /* Count/emit Huffman symbol for run length / number of bits */
 700    emit_ac_symbol(entropy, entropy->ac_tbl_no, (r << 4) + nbits);
 701
 702    /* Emit that number of bits of the value, if positive, */
 703    /* or the complement of its magnitude, if negative. */
 704    emit_bits_e(entropy, (unsigned int) temp2, nbits);
 705
 706    r = 0;			/* reset zero run length */
 707  }
 708
 709  if (r > 0) {			/* If there are trailing zeroes, */
 710    entropy->EOBRUN++;		/* count an EOB */
 711    if (entropy->EOBRUN == 0x7FFF)
 712      emit_eobrun(entropy);	/* force it out to avoid overflow */
 713  }
 714
 715  cinfo->dest->next_output_byte = entropy->next_output_byte;
 716  cinfo->dest->free_in_buffer = entropy->free_in_buffer;
 717
 718  /* Update restart-interval state too */
 719  if (cinfo->restart_interval) {
 720    if (entropy->restarts_to_go == 0) {
 721      entropy->restarts_to_go = cinfo->restart_interval;
 722      entropy->next_restart_num++;
 723      entropy->next_restart_num &= 7;
 724    }
 725    entropy->restarts_to_go--;
 726  }
 727
 728  return TRUE;
 729}
 730
 731
 732/*
 733 * MCU encoding for DC successive approximation refinement scan.
 734 * Note: we assume such scans can be multi-component, although the spec
 735 * is not very clear on the point.
 736 */
 737
 738METHODDEF(boolean)
 739encode_mcu_DC_refine (j_compress_ptr cinfo, JBLOCKROW *MCU_data)
 740{
 741  huff_entropy_ptr entropy = (huff_entropy_ptr) cinfo->entropy;
 742  register int temp;
 743  int blkn;
 744  int Al = cinfo->Al;
 745  JBLOCKROW block;
 746
 747  entropy->next_output_byte = cinfo->dest->next_output_byte;
 748  entropy->free_in_buffer = cinfo->dest->free_in_buffer;
 749
 750  /* Emit restart marker if needed */
 751  if (cinfo->restart_interval)
 752    if (entropy->restarts_to_go == 0)
 753      emit_restart_e(entropy, entropy->next_restart_num);
 754
 755  /* Encode the MCU data blocks */
 756  for (blkn = 0; blkn < cinfo->blocks_in_MCU; blkn++) {
 757    block = MCU_data[blkn];
 758
 759    /* We simply emit the Al'th bit of the DC coefficient value. */
 760    temp = (*block)[0];
 761    emit_bits_e(entropy, (unsigned int) (temp >> Al), 1);
 762  }
 763
 764  cinfo->dest->next_output_byte = entropy->next_output_byte;
 765  cinfo->dest->free_in_buffer = entropy->free_in_buffer;
 766
 767  /* Update restart-interval state too */
 768  if (cinfo->restart_interval) {
 769    if (entropy->restarts_to_go == 0) {
 770      entropy->restarts_to_go = cinfo->restart_interval;
 771      entropy->next_restart_num++;
 772      entropy->next_restart_num &= 7;
 773    }
 774    entropy->restarts_to_go--;
 775  }
 776
 777  return TRUE;
 778}
 779
 780
 781/*
 782 * MCU encoding for AC successive approximation refinement scan.
 783 */
 784
 785METHODDEF(boolean)
 786encode_mcu_AC_refine (j_compress_ptr cinfo, JBLOCKROW *MCU_data)
 787{
 788  huff_entropy_ptr entropy = (huff_entropy_ptr) cinfo->entropy;
 789  register int temp;
 790  register int r, k;
 791  int EOB;
 792  char *BR_buffer;
 793  unsigned int BR;
 794  int Se, Al;
 795  const int * natural_order;
 796  JBLOCKROW block;
 797  int absvalues[DCTSIZE2];
 798
 799  entropy->next_output_byte = cinfo->dest->next_output_byte;
 800  entropy->free_in_buffer = cinfo->dest->free_in_buffer;
 801
 802  /* Emit restart marker if needed */
 803  if (cinfo->restart_interval)
 804    if (entropy->restarts_to_go == 0)
 805      emit_restart_e(entropy, entropy->next_restart_num);
 806
 807  Se = cinfo->Se;
 808  Al = cinfo->Al;
 809  natural_order = cinfo->natural_order;
 810
 811  /* Encode the MCU data block */
 812  block = MCU_data[0];
 813
 814  /* It is convenient to make a pre-pass to determine the transformed
 815   * coefficients' absolute values and the EOB position.
 816   */
 817  EOB = 0;
 818  for (k = cinfo->Ss; k <= Se; k++) {
 819    temp = (*block)[natural_order[k]];
 820    /* We must apply the point transform by Al.  For AC coefficients this
 821     * is an integer division with rounding towards 0.  To do this portably
 822     * in C, we shift after obtaining the absolute value.
 823     */
 824    if (temp < 0)
 825      temp = -temp;		/* temp is abs value of input */
 826    temp >>= Al;		/* apply the point transform */
 827    absvalues[k] = temp;	/* save abs value for main pass */
 828    if (temp == 1)
 829      EOB = k;			/* EOB = index of last newly-nonzero coef */
 830  }
 831
 832  /* Encode the AC coefficients per section G.1.2.3, fig. G.7 */
 833  
 834  r = 0;			/* r = run length of zeros */
 835  BR = 0;			/* BR = count of buffered bits added now */
 836  BR_buffer = entropy->bit_buffer + entropy->BE; /* Append bits to buffer */
 837
 838  for (k = cinfo->Ss; k <= Se; k++) {
 839    if ((temp = absvalues[k]) == 0) {
 840      r++;
 841      continue;
 842    }
 843
 844    /* Emit any required ZRLs, but not if they can be folded into EOB */
 845    while (r > 15 && k <= EOB) {
 846      /* emit any pending EOBRUN and the BE correction bits */
 847      emit_eobrun(entropy);
 848      /* Emit ZRL */
 849      emit_ac_symbol(entropy, entropy->ac_tbl_no, 0xF0);
 850      r -= 16;
 851      /* Emit buffered correction bits that must be associated with ZRL */
 852      emit_buffered_bits(entropy, BR_buffer, BR);
 853      BR_buffer = entropy->bit_buffer; /* BE bits are gone now */
 854      BR = 0;
 855    }
 856
 857    /* If the coef was previously nonzero, it only needs a correction bit.
 858     * NOTE: a straight translation of the spec's figure G.7 would suggest
 859     * that we also need to test r > 15.  But if r > 15, we can only get here
 860     * if k > EOB, which implies that this coefficient is not 1.
 861     */
 862    if (temp > 1) {
 863      /* The correction bit is the next bit of the absolute value. */
 864      BR_buffer[BR++] = (char) (temp & 1);
 865      continue;
 866    }
 867
 868    /* Emit any pending EOBRUN and the BE correction bits */
 869    emit_eobrun(entropy);
 870
 871    /* Count/emit Huffman symbol for run length / number of bits */
 872    emit_ac_symbol(entropy, entropy->ac_tbl_no, (r << 4) + 1);
 873
 874    /* Emit output bit for newly-nonzero coef */
 875    temp = ((*block)[natural_order[k]] < 0) ? 0 : 1;
 876    emit_bits_e(entropy, (unsigned int) temp, 1);
 877
 878    /* Emit buffered correction bits that must be associated with this code */
 879    emit_buffered_bits(entropy, BR_buffer, BR);
 880    BR_buffer = entropy->bit_buffer; /* BE bits are gone now */
 881    BR = 0;
 882    r = 0;			/* reset zero run length */
 883  }
 884
 885  if (r > 0 || BR > 0) {	/* If there are trailing zeroes, */
 886    entropy->EOBRUN++;		/* count an EOB */
 887    entropy->BE += BR;		/* concat my correction bits to older ones */
 888    /* We force out the EOB if we risk either:
 889     * 1. overflow of the EOB counter;
 890     * 2. overflow of the correction bit buffer during the next MCU.
 891     */
 892    if (entropy->EOBRUN == 0x7FFF || entropy->BE > (MAX_CORR_BITS-DCTSIZE2+1))
 893      emit_eobrun(entropy);
 894  }
 895
 896  cinfo->dest->next_output_byte = entropy->next_output_byte;
 897  cinfo->dest->free_in_buffer = entropy->free_in_buffer;
 898
 899  /* Update restart-interval state too */
 900  if (cinfo->restart_interval) {
 901    if (entropy->restarts_to_go == 0) {
 902      entropy->restarts_to_go = cinfo->restart_interval;
 903      entropy->next_restart_num++;
 904      entropy->next_restart_num &= 7;
 905    }
 906    entropy->restarts_to_go--;
 907  }
 908
 909  return TRUE;
 910}
 911
 912
 913/* Encode a single block's worth of coefficients */
 914
 915LOCAL(boolean)
 916encode_one_block (working_state * state, JCOEFPTR block, int last_dc_val,
 917		  c_derived_tbl *dctbl, c_derived_tbl *actbl)
 918{
 919  register int temp, temp2;
 920  register int nbits;
 921  register int k, r, i;
 922  int Se = state->cinfo->lim_Se;
 923  const int * natural_order = state->cinfo->natural_order;
 924
 925  /* Encode the DC coefficient difference per section F.1.2.1 */
 926
 927  temp = temp2 = block[0] - last_dc_val;
 928
 929  if (temp < 0) {
 930    temp = -temp;		/* temp is abs value of input */
 931    /* For a negative input, want temp2 = bitwise complement of abs(input) */
 932    /* This code assumes we are on a two's complement machine */
 933    temp2--;
 934  }
 935
 936  /* Find the number of bits needed for the magnitude of the coefficient */
 937  nbits = 0;
 938  while (temp) {
 939    nbits++;
 940    temp >>= 1;
 941  }
 942  /* Check for out-of-range coefficient values.
 943   * Since we're encoding a difference, the range limit is twice as much.
 944   */
 945  if (nbits > MAX_COEF_BITS+1)
 946    ERREXIT(state->cinfo, JERR_BAD_DCT_COEF);
 947
 948  /* Emit the Huffman-coded symbol for the number of bits */
 949  if (! emit_bits_s(state, dctbl->ehufco[nbits], dctbl->ehufsi[nbits]))
 950    return FALSE;
 951
 952  /* Emit that number of bits of the value, if positive, */
 953  /* or the complement of its magnitude, if negative. */
 954  if (nbits)			/* emit_bits rejects calls with size 0 */
 955    if (! emit_bits_s(state, (unsigned int) temp2, nbits))
 956      return FALSE;
 957
 958  /* Encode the AC coefficients per section F.1.2.2 */
 959
 960  r = 0;			/* r = run length of zeros */
 961
 962  for (k = 1; k <= Se; k++) {
 963    if ((temp = block[natural_order[k]]) == 0) {
 964      r++;
 965    } else {
 966      /* if run length > 15, must emit special run-length-16 codes (0xF0) */
 967      while (r > 15) {
 968	if (! emit_bits_s(state, actbl->ehufco[0xF0], actbl->ehufsi[0xF0]))
 969	  return FALSE;
 970	r -= 16;
 971      }
 972
 973      temp2 = temp;
 974      if (temp < 0) {
 975	temp = -temp;		/* temp is abs value of input */
 976	/* This code assumes we are on a two's complement machine */
 977	temp2--;
 978      }
 979
 980      /* Find the number of bits needed for the magnitude of the coefficient */
 981      nbits = 1;		/* there must be at least one 1 bit */
 982      while ((temp >>= 1))
 983	nbits++;
 984      /* Check for out-of-range coefficient values */
 985      if (nbits > MAX_COEF_BITS)
 986	ERREXIT(state->cinfo, JERR_BAD_DCT_COEF);
 987
 988      /* Emit Huffman symbol for run length / number of bits */
 989      i = (r << 4) + nbits;
 990      if (! emit_bits_s(state, actbl->ehufco[i], actbl->ehufsi[i]))
 991	return FALSE;
 992
 993      /* Emit that number of bits of the value, if positive, */
 994      /* or the complement of its magnitude, if negative. */
 995      if (! emit_bits_s(state, (unsigned int) temp2, nbits))
 996	return FALSE;
 997
 998      r = 0;
 999    }
1000  }
1001
1002  /* If the last coef(s) were zero, emit an end-of-block code */
1003  if (r > 0)
1004    if (! emit_bits_s(state, actbl->ehufco[0], actbl->ehufsi[0]))
1005      return FALSE;
1006
1007  return TRUE;
1008}
1009
1010
1011/*
1012 * Encode and output one MCU's worth of Huffman-compressed coefficients.
1013 */
1014
1015METHODDEF(boolean)
1016encode_mcu_huff (j_compress_ptr cinfo, JBLOCKROW *MCU_data)
1017{
1018  huff_entropy_ptr entropy = (huff_entropy_ptr) cinfo->entropy;
1019  working_state state;
1020  int blkn, ci;
1021  jpeg_component_info * compptr;
1022
1023  /* Load up working state */
1024  state.next_output_byte = cinfo->dest->next_output_byte;
1025  state.free_in_buffer = cinfo->dest->free_in_buffer;
1026  ASSIGN_STATE(state.cur, entropy->saved);
1027  state.cinfo = cinfo;
1028
1029  /* Emit restart marker if needed */
1030  if (cinfo->restart_interval) {
1031    if (entropy->restarts_to_go == 0)
1032      if (! emit_restart_s(&state, entropy->next_restart_num))
1033	return FALSE;
1034  }
1035
1036  /* Encode the MCU data blocks */
1037  for (blkn = 0; blkn < cinfo->blocks_in_MCU; blkn++) {
1038    ci = cinfo->MCU_membership[blkn];
1039    compptr = cinfo->cur_comp_info[ci];
1040    if (! encode_one_block(&state,
1041			   MCU_data[blkn][0], state.cur.last_dc_val[ci],
1042			   entropy->dc_derived_tbls[compptr->dc_tbl_no],
1043			   entropy->ac_derived_tbls[compptr->ac_tbl_no]))
1044      return FALSE;
1045    /* Update last_dc_val */
1046    state.cur.last_dc_val[ci] = MCU_data[blkn][0][0];
1047  }
1048
1049  /* Completed MCU, so update state */
1050  cinfo->dest->next_output_byte = state.next_output_byte;
1051  cinfo->dest->free_in_buffer = state.free_in_buffer;
1052  ASSIGN_STATE(entropy->saved, state.cur);
1053
1054  /* Update restart-interval state too */
1055  if (cinfo->restart_interval) {
1056    if (entropy->restarts_to_go == 0) {
1057      entropy->restarts_to_go = cinfo->restart_interval;
1058      entropy->next_restart_num++;
1059      entropy->next_restart_num &= 7;
1060    }
1061    entropy->restarts_to_go--;
1062  }
1063
1064  return TRUE;
1065}
1066
1067
1068/*
1069 * Finish up at the end of a Huffman-compressed scan.
1070 */
1071
1072METHODDEF(void)
1073finish_pass_huff (j_compress_ptr cinfo)
1074{
1075  huff_entropy_ptr entropy = (huff_entropy_ptr) cinfo->entropy;
1076  working_state state;
1077
1078  if (cinfo->progressive_mode) {
1079    entropy->next_output_byte = cinfo->dest->next_output_byte;
1080    entropy->free_in_buffer = cinfo->dest->free_in_buffer;
1081
1082    /* Flush out any buffered data */
1083    emit_eobrun(entropy);
1084    flush_bits_e(entropy);
1085
1086    cinfo->dest->next_output_byte = entropy->next_output_byte;
1087    cinfo->dest->free_in_buffer = entropy->free_in_buffer;
1088  } else {
1089    /* Load up working state ... flush_bits needs it */
1090    state.next_output_byte = cinfo->dest->next_output_byte;
1091    state.free_in_buffer = cinfo->dest->free_in_buffer;
1092    ASSIGN_STATE(state.cur, entropy->saved);
1093    state.cinfo = cinfo;
1094
1095    /* Flush out the last data */
1096    if (! flush_bits_s(&state))
1097      ERREXIT(cinfo, JERR_CANT_SUSPEND);
1098
1099    /* Update state */
1100    cinfo->dest->next_output_byte = state.next_output_byte;
1101    cinfo->dest->free_in_buffer = state.free_in_buffer;
1102    ASSIGN_STATE(entropy->saved, state.cur);
1103  }
1104}
1105
1106
1107/*
1108 * Huffman coding optimization.
1109 *
1110 * We first scan the supplied data and count the number of uses of each symbol
1111 * that is to be Huffman-coded. (This process MUST agree with the code above.)
1112 * Then we build a Huffman coding tree for the observed counts.
1113 * Symbols which are not needed at all for the particular image are not
1114 * assigned any code, which saves space in the DHT marker as well as in
1115 * the compressed data.
1116 */
1117
1118
1119/* Process a single block's worth of coefficients */
1120
1121LOCAL(void)
1122htest_one_block (j_compress_ptr cinfo, JCOEFPTR block, int last_dc_val,
1123		 long dc_counts[], long ac_counts[])
1124{
1125  register int temp;
1126  register int nbits;
1127  register int k, r;
1128  int Se = cinfo->lim_Se;
1129  const int * natural_order = cinfo->natural_order;
1130  
1131  /* Encode the DC coefficient difference per section F.1.2.1 */
1132  
1133  temp = block[0] - last_dc_val;
1134  if (temp < 0)
1135    temp = -temp;
1136  
1137  /* Find the number of bits needed for the magnitude of the coefficient */
1138  nbits = 0;
1139  while (temp) {
1140    nbits++;
1141    temp >>= 1;
1142  }
1143  /* Check for out-of-range coefficient values.
1144   * Since we're encoding a difference, the range limit is twice as much.
1145   */
1146  if (nbits > MAX_COEF_BITS+1)
1147    ERREXIT(cinfo, JERR_BAD_DCT_COEF);
1148
1149  /* Count the Huffman symbol for the number of bits */
1150  dc_counts[nbits]++;
1151  
1152  /* Encode the AC coefficients per section F.1.2.2 */
1153  
1154  r = 0;			/* r = run length of zeros */
1155  
1156  for (k = 1; k <= Se; k++) {
1157    if ((temp = block[natural_order[k]]) == 0) {
1158      r++;
1159    } else {
1160      /* if run length > 15, must emit special run-length-16 codes (0xF0) */
1161      while (r > 15) {
1162	ac_counts[0xF0]++;
1163	r -= 16;
1164      }
1165      
1166      /* Find the number of bits needed for the magnitude of the coefficient */
1167      if (temp < 0)
1168	temp = -temp;
1169      
1170      /* Find the number of bits needed for the magnitude of the coefficient */
1171      nbits = 1;		/* there must be at least one 1 bit */
1172      while ((temp >>= 1))
1173	nbits++;
1174      /* Check for out-of-range coefficient values */
1175      if (nbits > MAX_COEF_BITS)
1176	ERREXIT(cinfo, JERR_BAD_DCT_COEF);
1177      
1178      /* Count Huffman symbol for run length / number of bits */
1179      ac_counts[(r << 4) + nbits]++;
1180      
1181      r = 0;
1182    }
1183  }
1184
1185  /* If the last coef(s) were zero, emit an end-of-block code */
1186  if (r > 0)
1187    ac_counts[0]++;
1188}
1189
1190
1191/*
1192 * Trial-encode one MCU's worth of Huffman-compressed coefficients.
1193 * No data is actually output, so no suspension return is possible.
1194 */
1195
1196METHODDEF(boolean)
1197encode_mcu_gather (j_compress_ptr cinfo, JBLOCKROW *MCU_data)
1198{
1199  huff_entropy_ptr entropy = (huff_entropy_ptr) cinfo->entropy;
1200  int blkn, ci;
1201  jpeg_component_info * compptr;
1202
1203  /* Take care of restart intervals if needed */
1204  if (cinfo->restart_interval) {
1205    if (entropy->restarts_to_go == 0) {
1206      /* Re-initialize DC predictions to 0 */
1207      for (ci = 0; ci < cinfo->comps_in_scan; ci++)
1208	entropy->saved.last_dc_val[ci] = 0;
1209      /* Update restart state */
1210      entropy->restarts_to_go = cinfo->restart_interval;
1211    }
1212    entropy->restarts_to_go--;
1213  }
1214
1215  for (blkn = 0; blkn < cinfo->blocks_in_MCU; blkn++) {
1216    ci = cinfo->MCU_membership[blkn];
1217    compptr = cinfo->cur_comp_info[ci];
1218    htest_one_block(cinfo, MCU_data[blkn][0], entropy->saved.last_dc_val[ci],
1219		    entropy->dc_count_ptrs[compptr->dc_tbl_no],
1220		    entropy->ac_count_ptrs[compptr->ac_tbl_no]);
1221    entropy->saved.last_dc_val[ci] = MCU_data[blkn][0][0];
1222  }
1223
1224  return TRUE;
1225}
1226
1227
1228/*
1229 * Generate the best Huffman code table for the given counts, fill htbl.
1230 *
1231 * The JPEG standard requires that no symbol be assigned a codeword of all
1232 * one bits (so that padding bits added at the end of a compressed segment
1233 * can't look like a valid code).  Because of the canonical ordering of
1234 * codewords, this just means that there must be an unused slot in the
1235 * longest codeword length category.  Section K.2 of the JPEG spec suggests
1236 * reserving such a slot by pretending that symbol 256 is a valid symbol
1237 * with count 1.  In theory that's not optimal; giving it count zero but
1238 * including it in the symbol set anyway should give a better Huffman code.
1239 * But the theoretically better code actually seems to come out worse in
1240 * practice, because it produces more all-ones bytes (which incur stuffed
1241 * zero bytes in the final file).  In any case the difference is tiny.
1242 *
1243 * The JPEG standard requires Huffman codes to be no more than 16 bits long.
1244 * If some symbols have a very small but nonzero probability, the Huffman tree
1245 * must be adjusted to meet the code length restriction.  We currently use
1246 * the adjustment method suggested in JPEG section K.2.  This method is *not*
1247 * optimal; it may not choose the best possible limited-length code.  But
1248 * typically only very-low-frequency symbols will be given less-than-optimal
1249 * lengths, so the code is almost optimal.  Experimental comparisons against
1250 * an optimal limited-length-code algorithm indicate that the difference is
1251 * microscopic --- usually less than a hundredth of a percent of total size.
1252 * So the extra complexity of an optimal algorithm doesn't seem worthwhile.
1253 */
1254
1255LOCAL(void)
1256jpeg_gen_optimal_table (j_compress_ptr cinfo, JHUFF_TBL * htbl, long freq[])
1257{
1258#define MAX_CLEN 32		/* assumed maximum initial code length */
1259  UINT8 bits[MAX_CLEN+1];	/* bits[k] = # of symbols with code length k */
1260  int codesize[257];		/* codesize[k] = code length of symbol k */
1261  int others[257];		/* next symbol in current branch of tree */
1262  int c1, c2;
1263  int p, i, j;
1264  long v;
1265
1266  /* This algorithm is explained in section K.2 of the JPEG standard */
1267
1268  MEMZERO(bits, SIZEOF(bits));
1269  MEMZERO(codesize, SIZEOF(codesize));
1270  for (i = 0; i < 257; i++)
1271    others[i] = -1;		/* init links to empty */
1272  
1273  freq[256] = 1;		/* make sure 256 has a nonzero count */
1274  /* Including the pseudo-symbol 256 in the Huffman procedure guarantees
1275   * that no real symbol is given code-value of all ones, because 256
1276   * will be placed last in the largest codeword category.
1277   */
1278
1279  /* Huffman's basic algorithm to assign optimal code lengths to symbols */
1280
1281  for (;;) {
1282    /* Find the smallest nonzero frequency, set c1 = its symbol */
1283    /* In case of ties, take the larger symbol number */
1284    c1 = -1;
1285    v = 1000000000L;
1286    for (i = 0; i <= 256; i++) {
1287      if (freq[i] && freq[i] <= v) {
1288	v = freq[i];
1289	c1 = i;
1290      }
1291    }
1292
1293    /* Find the next smallest nonzero frequency, set c2 = its symbol */
1294    /* In case of ties, take the larger symbol number */
1295    c2 = -1;
1296    v = 1000000000L;
1297    for (i = 0; i <= 256; i++) {
1298      if (freq[i] && freq[i] <= v && i != c1) {
1299	v = freq[i];
1300	c2 = i;
1301      }
1302    }
1303
1304    /* Done if we've merged everything into one frequency */
1305    if (c2 < 0)
1306      break;
1307    
1308    /* Else merge the two counts/trees */
1309    freq[c1] += freq[c2];
1310    freq[c2] = 0;
1311
1312    /* Increment the codesize of everything in c1's tree branch */
1313    codesize[c1]++;
1314    while (others[c1] >= 0) {
1315      c1 = others[c1];
1316      codesize[c1]++;
1317    }
1318    
1319    others[c1] = c2;		/* chain c2 onto c1's tree branch */
1320    
1321    /* Increment the codesize of everything in c2's tree branch */
1322    codesize[c2]++;
1323    while (others[c2] >= 0) {
1324      c2 = others[c2];
1325      codesize[c2]++;
1326    }
1327  }
1328
1329  /* Now count the number of symbols of each code length */
1330  for (i = 0; i <= 256; i++) {
1331    if (codesize[i]) {
1332      /* The JPEG standard seems to think that this can't happen, */
1333      /* but I'm paranoid... */
1334      if (codesize[i] > MAX_CLEN)
1335	ERREXIT(cinfo, JERR_HUFF_CLEN_OVERFLOW);
1336
1337      bits[codesize[i]]++;
1338    }
1339  }
1340
1341  /* JPEG doesn't allow symbols with code lengths over 16 bits, so if the pure
1342   * Huffman procedure assigned any such lengths, we must adjust the coding.
1343   * Here is what the JPEG spec says about how this next bit works:
1344   * Since symbols are paired for the longest Huffman code, the symbols are
1345   * removed from this length category two at a time.  The prefix for the pair
1346   * (which is one bit shorter) is allocated to one of the pair; then,
1347   * skipping the BITS entry for that prefix length, a code word from the next
1348   * shortest nonzero BITS entry is converted into a prefix for two code words
1349   * one bit longer.
1350   */
1351  
1352  for (i = MAX_CLEN; i > 16; i--) {
1353    while (bits[i] > 0) {
1354      j = i - 2;		/* find length of new prefix to be used */
1355      while (bits[j] == 0)
1356	j--;
1357      
1358      bits[i] -= 2;		/* remove two symbols */
1359      bits[i-1]++;		/* one goes in this length */
1360      bits[j+1] += 2;		/* two new symbols in this length */
1361      bits[j]--;		/* symbol of this length is now a prefix */
1362    }
1363  }
1364
1365  /* Remove the count for the pseudo-symbol 256 from the largest codelength */
1366  while (bits[i] == 0)		/* find largest codelength still in use */
1367    i--;
1368  bits[i]--;
1369  
1370  /* Return final symbol counts (only for lengths 0..16) */
1371  MEMCOPY(htbl->bits, bits, SIZEOF(htbl->bits));
1372  
1373  /* Return a list of the symbols sorted by code length */
1374  /* It's not real clear to me why we don't need to consider the codelength
1375   * changes made above, but the JPEG spec seems to think this works.
1376   */
1377  p = 0;
1378  for (i = 1; i <= MAX_CLEN; i++) {
1379    for (j = 0; j <= 255; j++) {
1380      if (codesize[j] == i) {
1381	htbl->huffval[p] = (UINT8) j;
1382	p++;
1383      }
1384    }
1385  }
1386
1387  /* Set sent_table FALSE so updated table will be written to JPEG file. */
1388  htbl->sent_table = FALSE;
1389}
1390
1391
1392/*
1393 * Finish up a statistics-gathering pass and create the new Huffman tables.
1394 */
1395
1396METHODDEF(void)
1397finish_pass_gather (j_compress_ptr cinfo)
1398{
1399  huff_entropy_ptr entropy = (huff_entropy_ptr) cinfo->entropy;
1400  int ci, tbl;
1401  jpeg_component_info * compptr;
1402  JHUFF_TBL **htblptr;
1403  boolean did_dc[NUM_HUFF_TBLS];
1404  boolean did_ac[NUM_HUFF_TBLS];
1405
1406  /* It's important not to apply jpeg_gen_optimal_table more than once
1407   * per table, because it clobbers the input frequency counts!
1408   */
1409  if (cinfo->progressive_mode)
1410    /* Flush out buffered data (all we care about is counting the EOB symbol) */
1411    emit_eobrun(entropy);
1412
1413  MEMZERO(did_dc, SIZEOF(did_dc));
1414  MEMZERO(did_ac, SIZEOF(did_ac));
1415
1416  for (ci = 0; ci < cinfo->comps_in_scan; ci++) {
1417    compptr = cinfo->cur_comp_info[ci];
1418    /* DC needs no table for refinement scan */
1419    if (cinfo->Ss == 0 && cinfo->Ah == 0) {
1420      tbl = compptr->dc_tbl_no;
1421      if (! did_dc[tbl]) {
1422	htblptr = & cinfo->dc_huff_tbl_ptrs[tbl];
1423	if (*htblptr == NULL)
1424	  *htblptr = jpeg_alloc_huff_table((j_common_ptr) cinfo);
1425	jpeg_gen_optimal_table(cinfo, *htblptr, entropy->dc_count_ptrs[tbl]);
1426	did_dc[tbl] = TRUE;
1427      }
1428    }
1429    /* AC needs no table when not present */
1430    if (cinfo->Se) {
1431      tbl = compptr->ac_tbl_no;
1432      if (! did_ac[tbl]) {
1433	htblptr = & cinfo->ac_huff_tbl_ptrs[tbl];
1434	if (*htblptr == NULL)
1435	  *htblptr = jpeg_alloc_huff_table((j_common_ptr) cinfo);
1436	jpeg_gen_optimal_table(cinfo, *htblptr, entropy->ac_count_ptrs[tbl]);
1437	did_ac[tbl] = TRUE;
1438      }
1439    }
1440  }
1441}
1442
1443
1444/*
1445 * Initialize for a Huffman-compressed scan.
1446 * If gather_statistics is TRUE, we do not output anything during the scan,
1447 * just count the Huffman symbols used and generate Huffman code tables.
1448 */
1449
1450METHODDEF(void)
1451start_pass_huff (j_compress_ptr cinfo, boolean gather_statistics)
1452{
1453  huff_entropy_ptr entropy = (huff_entropy_ptr) cinfo->entropy;
1454  int ci, tbl;
1455  jpeg_component_info * compptr;
1456
1457  if (gather_statistics)
1458    entropy->pub.finish_pass = finish_pass_gather;
1459  else
1460    entropy->pub.finish_pass = finish_pass_huff;
1461
1462  if (cinfo->progressive_mode) {
1463    entropy->cinfo = cinfo;
1464    entropy->gather_statistics = gather_statistics;
1465
1466    /* We assume jcmaster.c already validated the scan parameters. */
1467
1468    /* Select execution routine */
1469    if (cinfo->Ah == 0) {
1470      if (cinfo->Ss == 0)
1471	entropy->pub.encode_mcu = encode_mcu_DC_first;
1472      else
1473	entropy->pub.encode_mcu = encode_mcu_AC_first;
1474    } else {
1475      if (cinfo->Ss == 0)
1476	entropy->pub.encode_mcu = encode_mcu_DC_refine;
1477      else {
1478	entropy->pub.encode_mcu = encode_mcu_AC_refine;
1479	/* AC refinement needs a correction bit buffer */
1480	if (entropy->bit_buffer == NULL)
1481	  entropy->bit_buffer = (char *)
1482	    (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE,
1483					MAX_CORR_BITS * SIZEOF(char));
1484      }
1485    }
1486
1487    /* Initialize AC stuff */
1488    entropy->ac_tbl_no = cinfo->cur_comp_info[0]->ac_tbl_no;
1489    entropy->EOBRUN = 0;
1490    entropy->BE = 0;
1491  } else {
1492    if (gather_statistics)
1493      entropy->pub.encode_mcu = encode_mcu_gather;
1494    else
1495      entropy->pub.encode_mcu = encode_mcu_huff;
1496  }
1497
1498  for (ci = 0; ci < cinfo->comps_in_scan; ci++) {
1499    compptr = cinfo->cur_comp_info[ci];
1500    /* DC needs no table for refinement scan */
1501    if (cinfo->Ss == 0 && cinfo->Ah == 0) {
1502      tbl = compptr->dc_tbl_no;
1503      if (gather_statistics) {
1504	/* Check for invalid table index */
1505	/* (make_c_derived_tbl does this in the other path) */
1506	if (tbl < 0 || tbl >= NUM_HUFF_TBLS)
1507	  ERREXIT1(cinfo, JERR_NO_HUFF_TABLE, tbl);
1508	/* Allocate and zero the statistics tables */
1509	/* Note that jpeg_gen_optimal_table expects 257 entries in each table! */
1510	if (entropy->dc_count_ptrs[tbl] == NULL)
1511	  entropy->dc_count_ptrs[tbl] = (long *)
1512	    (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE,
1513					257 * SIZEOF(long));
1514	MEMZERO(entropy->dc_count_ptrs[tbl], 257 * SIZEOF(long));
1515      } else {
1516	/* Compute derived values for Huffman tables */
1517	/* We may do this more than once for a table, but it's not expensive */
1518	jpeg_make_c_derived_tbl(cinfo, TRUE, tbl,
1519				& entropy->dc_derived_tbls[tbl]);
1520      }
1521      /* Initialize DC predictions to 0 */
1522      entropy->saved.last_dc_val[ci] = 0;
1523    }
1524    /* AC needs no table when not present */
1525    if (cinfo->Se) {
1526      tbl = compptr->ac_tbl_no;
1527      if (gather_statistics) {
1528	if (tbl < 0 || tbl >= NUM_HUFF_TBLS)
1529	  ERREXIT1(cinfo, JERR_NO_HUFF_TABLE, tbl);
1530	if (entropy->ac_count_ptrs[tbl] == NULL)
1531	  entropy->ac_count_ptrs[tbl] = (long *)
1532	    (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE,
1533					257 * SIZEOF(long));
1534	MEMZERO(entropy->ac_count_ptrs[tbl], 257 * SIZEOF(long));
1535      } else {
1536	jpeg_make_c_derived_tbl(cinfo, FALSE, tbl,
1537				& entropy->ac_derived_tbls[tbl]);
1538      }
1539    }
1540  }
1541
1542  /* Initialize bit buffer to empty */
1543  entropy->saved.put_buffer = 0;
1544  entropy->saved.put_bits = 0;
1545
1546  /* Initialize restart stuff */
1547  entropy->restarts_to_go = cinfo->restart_interval;
1548  entropy->next_restart_num = 0;
1549}
1550
1551
1552/*
1553 * Module initialization routine for Huffman entropy encoding.
1554 */
1555
1556GLOBAL(void)
1557jinit_huff_encoder (j_compress_ptr cinfo)
1558{
1559  huff_entropy_ptr entropy;
1560  int i;
1561
1562  entropy = (huff_entropy_ptr)
1563    (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE,
1564				SIZEOF(huff_entropy_encoder));
1565  cinfo->entropy = (struct jpeg_entropy_encoder *) entropy;
1566  entropy->pub.start_pass = start_pass_huff;
1567
1568  /* Mark tables unallocated */
1569  for (i = 0; i < NUM_HUFF_TBLS; i++) {
1570    entropy->dc_derived_tbls[i] = entropy->ac_derived_tbls[i] = NULL;
1571    entropy->dc_count_ptrs[i] = entropy->ac_count_ptrs[i] = NULL;
1572  }
1573
1574  if (cinfo->progressive_mode)
1575    entropy->bit_buffer = NULL;	/* needed only in AC refinement scan */
1576}