J. Duke | 319a3b9 | 2007-12-01 00:00:00 +0000 | [diff] [blame^] | 1 | /* |
| 2 | * reserved comment block |
| 3 | * DO NOT REMOVE OR ALTER! |
| 4 | */ |
| 5 | /* |
| 6 | * jchuff.c |
| 7 | * |
| 8 | * Copyright (C) 1991-1997, 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. |
| 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 "jchuff.h" /* Declarations shared with jcphuff.c */ |
| 25 | |
| 26 | |
| 27 | /* Expanded entropy encoder object for Huffman encoding. |
| 28 | * |
| 29 | * The savable_state subrecord contains fields that change within an MCU, |
| 30 | * but must not be updated permanently until we complete the MCU. |
| 31 | */ |
| 32 | |
| 33 | typedef struct { |
| 34 | INT32 put_buffer; /* current bit-accumulation buffer */ |
| 35 | int put_bits; /* # of bits now in it */ |
| 36 | int last_dc_val[MAX_COMPS_IN_SCAN]; /* last DC coef for each component */ |
| 37 | } savable_state; |
| 38 | |
| 39 | /* This macro is to work around compilers with missing or broken |
| 40 | * structure assignment. You'll need to fix this code if you have |
| 41 | * such a compiler and you change MAX_COMPS_IN_SCAN. |
| 42 | */ |
| 43 | |
| 44 | #ifndef NO_STRUCT_ASSIGN |
| 45 | #define ASSIGN_STATE(dest,src) ((dest) = (src)) |
| 46 | #else |
| 47 | #if MAX_COMPS_IN_SCAN == 4 |
| 48 | #define ASSIGN_STATE(dest,src) \ |
| 49 | ((dest).put_buffer = (src).put_buffer, \ |
| 50 | (dest).put_bits = (src).put_bits, \ |
| 51 | (dest).last_dc_val[0] = (src).last_dc_val[0], \ |
| 52 | (dest).last_dc_val[1] = (src).last_dc_val[1], \ |
| 53 | (dest).last_dc_val[2] = (src).last_dc_val[2], \ |
| 54 | (dest).last_dc_val[3] = (src).last_dc_val[3]) |
| 55 | #endif |
| 56 | #endif |
| 57 | |
| 58 | |
| 59 | typedef struct { |
| 60 | struct jpeg_entropy_encoder pub; /* public fields */ |
| 61 | |
| 62 | savable_state saved; /* Bit buffer & DC state at start of MCU */ |
| 63 | |
| 64 | /* These fields are NOT loaded into local working state. */ |
| 65 | unsigned int restarts_to_go; /* MCUs left in this restart interval */ |
| 66 | int next_restart_num; /* next restart number to write (0-7) */ |
| 67 | |
| 68 | /* Pointers to derived tables (these workspaces have image lifespan) */ |
| 69 | c_derived_tbl * dc_derived_tbls[NUM_HUFF_TBLS]; |
| 70 | c_derived_tbl * ac_derived_tbls[NUM_HUFF_TBLS]; |
| 71 | |
| 72 | #ifdef ENTROPY_OPT_SUPPORTED /* Statistics tables for optimization */ |
| 73 | long * dc_count_ptrs[NUM_HUFF_TBLS]; |
| 74 | long * ac_count_ptrs[NUM_HUFF_TBLS]; |
| 75 | #endif |
| 76 | } huff_entropy_encoder; |
| 77 | |
| 78 | typedef huff_entropy_encoder * huff_entropy_ptr; |
| 79 | |
| 80 | /* Working state while writing an MCU. |
| 81 | * This struct contains all the fields that are needed by subroutines. |
| 82 | */ |
| 83 | |
| 84 | typedef struct { |
| 85 | JOCTET * next_output_byte; /* => next byte to write in buffer */ |
| 86 | size_t free_in_buffer; /* # of byte spaces remaining in buffer */ |
| 87 | savable_state cur; /* Current bit buffer & DC state */ |
| 88 | j_compress_ptr cinfo; /* dump_buffer needs access to this */ |
| 89 | } working_state; |
| 90 | |
| 91 | |
| 92 | /* Forward declarations */ |
| 93 | METHODDEF(boolean) encode_mcu_huff JPP((j_compress_ptr cinfo, |
| 94 | JBLOCKROW *MCU_data)); |
| 95 | METHODDEF(void) finish_pass_huff JPP((j_compress_ptr cinfo)); |
| 96 | #ifdef ENTROPY_OPT_SUPPORTED |
| 97 | METHODDEF(boolean) encode_mcu_gather JPP((j_compress_ptr cinfo, |
| 98 | JBLOCKROW *MCU_data)); |
| 99 | METHODDEF(void) finish_pass_gather JPP((j_compress_ptr cinfo)); |
| 100 | #endif |
| 101 | |
| 102 | |
| 103 | /* |
| 104 | * Initialize for a Huffman-compressed scan. |
| 105 | * If gather_statistics is TRUE, we do not output anything during the scan, |
| 106 | * just count the Huffman symbols used and generate Huffman code tables. |
| 107 | */ |
| 108 | |
| 109 | METHODDEF(void) |
| 110 | start_pass_huff (j_compress_ptr cinfo, boolean gather_statistics) |
| 111 | { |
| 112 | huff_entropy_ptr entropy = (huff_entropy_ptr) cinfo->entropy; |
| 113 | int ci, dctbl, actbl; |
| 114 | jpeg_component_info * compptr; |
| 115 | |
| 116 | if (gather_statistics) { |
| 117 | #ifdef ENTROPY_OPT_SUPPORTED |
| 118 | entropy->pub.encode_mcu = encode_mcu_gather; |
| 119 | entropy->pub.finish_pass = finish_pass_gather; |
| 120 | #else |
| 121 | ERREXIT(cinfo, JERR_NOT_COMPILED); |
| 122 | #endif |
| 123 | } else { |
| 124 | entropy->pub.encode_mcu = encode_mcu_huff; |
| 125 | entropy->pub.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 | /* |
| 176 | * Compute the derived values for a Huffman table. |
| 177 | * This routine also performs some validation checks on the table. |
| 178 | * |
| 179 | * Note this is also used by jcphuff.c. |
| 180 | */ |
| 181 | |
| 182 | GLOBAL(void) |
| 183 | jpeg_make_c_derived_tbl (j_compress_ptr cinfo, boolean isDC, int tblno, |
| 184 | c_derived_tbl ** pdtbl) |
| 185 | { |
| 186 | JHUFF_TBL *htbl; |
| 187 | c_derived_tbl *dtbl; |
| 188 | int p, i, l, lastp, si, maxsymbol; |
| 189 | char huffsize[257]; |
| 190 | unsigned int huffcode[257]; |
| 191 | unsigned int code; |
| 192 | |
| 193 | /* Note that huffsize[] and huffcode[] are filled in code-length order, |
| 194 | * paralleling the order of the symbols themselves in htbl->huffval[]. |
| 195 | */ |
| 196 | |
| 197 | /* Find the input Huffman table */ |
| 198 | if (tblno < 0 || tblno >= NUM_HUFF_TBLS) |
| 199 | ERREXIT1(cinfo, JERR_NO_HUFF_TABLE, tblno); |
| 200 | htbl = |
| 201 | isDC ? cinfo->dc_huff_tbl_ptrs[tblno] : cinfo->ac_huff_tbl_ptrs[tblno]; |
| 202 | if (htbl == NULL) |
| 203 | ERREXIT1(cinfo, JERR_NO_HUFF_TABLE, tblno); |
| 204 | |
| 205 | /* Allocate a workspace if we haven't already done so. */ |
| 206 | if (*pdtbl == NULL) |
| 207 | *pdtbl = (c_derived_tbl *) |
| 208 | (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE, |
| 209 | SIZEOF(c_derived_tbl)); |
| 210 | dtbl = *pdtbl; |
| 211 | |
| 212 | /* Figure C.1: make table of Huffman code length for each symbol */ |
| 213 | |
| 214 | p = 0; |
| 215 | for (l = 1; l <= 16; l++) { |
| 216 | i = (int) htbl->bits[l]; |
| 217 | if (i < 0 || p + i > 256) /* protect against table overrun */ |
| 218 | ERREXIT(cinfo, JERR_BAD_HUFF_TABLE); |
| 219 | while (i--) |
| 220 | huffsize[p++] = (char) l; |
| 221 | } |
| 222 | huffsize[p] = 0; |
| 223 | lastp = p; |
| 224 | |
| 225 | /* Figure C.2: generate the codes themselves */ |
| 226 | /* We also validate that the counts represent a legal Huffman code tree. */ |
| 227 | |
| 228 | code = 0; |
| 229 | si = huffsize[0]; |
| 230 | p = 0; |
| 231 | while (huffsize[p]) { |
| 232 | while (((int) huffsize[p]) == si) { |
| 233 | huffcode[p++] = code; |
| 234 | code++; |
| 235 | } |
| 236 | /* code is now 1 more than the last code used for codelength si; but |
| 237 | * it must still fit in si bits, since no code is allowed to be all ones. |
| 238 | */ |
| 239 | if (((INT32) code) >= (((INT32) 1) << si)) |
| 240 | ERREXIT(cinfo, JERR_BAD_HUFF_TABLE); |
| 241 | code <<= 1; |
| 242 | si++; |
| 243 | } |
| 244 | |
| 245 | /* Figure C.3: generate encoding tables */ |
| 246 | /* These are code and size indexed by symbol value */ |
| 247 | |
| 248 | /* Set all codeless symbols to have code length 0; |
| 249 | * this lets us detect duplicate VAL entries here, and later |
| 250 | * allows emit_bits to detect any attempt to emit such symbols. |
| 251 | */ |
| 252 | MEMZERO(dtbl->ehufsi, SIZEOF(dtbl->ehufsi)); |
| 253 | |
| 254 | /* This is also a convenient place to check for out-of-range |
| 255 | * and duplicated VAL entries. We allow 0..255 for AC symbols |
| 256 | * but only 0..15 for DC. (We could constrain them further |
| 257 | * based on data depth and mode, but this seems enough.) |
| 258 | */ |
| 259 | maxsymbol = isDC ? 15 : 255; |
| 260 | |
| 261 | for (p = 0; p < lastp; p++) { |
| 262 | i = htbl->huffval[p]; |
| 263 | if (i < 0 || i > maxsymbol || dtbl->ehufsi[i]) |
| 264 | ERREXIT(cinfo, JERR_BAD_HUFF_TABLE); |
| 265 | dtbl->ehufco[i] = huffcode[p]; |
| 266 | dtbl->ehufsi[i] = huffsize[p]; |
| 267 | } |
| 268 | } |
| 269 | |
| 270 | |
| 271 | /* Outputting bytes to the file */ |
| 272 | |
| 273 | /* Emit a byte, taking 'action' if must suspend. */ |
| 274 | #define emit_byte(state,val,action) \ |
| 275 | { *(state)->next_output_byte++ = (JOCTET) (val); \ |
| 276 | if (--(state)->free_in_buffer == 0) \ |
| 277 | if (! dump_buffer(state)) \ |
| 278 | { action; } } |
| 279 | |
| 280 | |
| 281 | LOCAL(boolean) |
| 282 | dump_buffer (working_state * state) |
| 283 | /* Empty the output buffer; return TRUE if successful, FALSE if must suspend */ |
| 284 | { |
| 285 | struct jpeg_destination_mgr * dest = state->cinfo->dest; |
| 286 | |
| 287 | if (! (*dest->empty_output_buffer) (state->cinfo)) |
| 288 | return FALSE; |
| 289 | /* After a successful buffer dump, must reset buffer pointers */ |
| 290 | state->next_output_byte = dest->next_output_byte; |
| 291 | state->free_in_buffer = dest->free_in_buffer; |
| 292 | return TRUE; |
| 293 | } |
| 294 | |
| 295 | |
| 296 | /* Outputting bits to the file */ |
| 297 | |
| 298 | /* Only the right 24 bits of put_buffer are used; the valid bits are |
| 299 | * left-justified in this part. At most 16 bits can be passed to emit_bits |
| 300 | * in one call, and we never retain more than 7 bits in put_buffer |
| 301 | * between calls, so 24 bits are sufficient. |
| 302 | */ |
| 303 | |
| 304 | INLINE |
| 305 | LOCAL(boolean) |
| 306 | emit_bits (working_state * state, unsigned int code, int size) |
| 307 | /* Emit some bits; return TRUE if successful, FALSE if must suspend */ |
| 308 | { |
| 309 | /* This routine is heavily used, so it's worth coding tightly. */ |
| 310 | register INT32 put_buffer = (INT32) code; |
| 311 | register int put_bits = state->cur.put_bits; |
| 312 | |
| 313 | /* if size is 0, caller used an invalid Huffman table entry */ |
| 314 | if (size == 0) |
| 315 | ERREXIT(state->cinfo, JERR_HUFF_MISSING_CODE); |
| 316 | |
| 317 | put_buffer &= (((INT32) 1)<<size) - 1; /* mask off any extra bits in code */ |
| 318 | |
| 319 | put_bits += size; /* new number of bits in buffer */ |
| 320 | |
| 321 | put_buffer <<= 24 - put_bits; /* align incoming bits */ |
| 322 | |
| 323 | put_buffer |= state->cur.put_buffer; /* and merge with old buffer contents */ |
| 324 | |
| 325 | while (put_bits >= 8) { |
| 326 | int c = (int) ((put_buffer >> 16) & 0xFF); |
| 327 | |
| 328 | emit_byte(state, c, return FALSE); |
| 329 | if (c == 0xFF) { /* need to stuff a zero byte? */ |
| 330 | emit_byte(state, 0, return FALSE); |
| 331 | } |
| 332 | put_buffer <<= 8; |
| 333 | put_bits -= 8; |
| 334 | } |
| 335 | |
| 336 | state->cur.put_buffer = put_buffer; /* update state variables */ |
| 337 | state->cur.put_bits = put_bits; |
| 338 | |
| 339 | return TRUE; |
| 340 | } |
| 341 | |
| 342 | |
| 343 | LOCAL(boolean) |
| 344 | flush_bits (working_state * state) |
| 345 | { |
| 346 | if (! emit_bits(state, 0x7F, 7)) /* fill any partial byte with ones */ |
| 347 | return FALSE; |
| 348 | state->cur.put_buffer = 0; /* and reset bit-buffer to empty */ |
| 349 | state->cur.put_bits = 0; |
| 350 | return TRUE; |
| 351 | } |
| 352 | |
| 353 | |
| 354 | /* Encode a single block's worth of coefficients */ |
| 355 | |
| 356 | LOCAL(boolean) |
| 357 | encode_one_block (working_state * state, JCOEFPTR block, int last_dc_val, |
| 358 | c_derived_tbl *dctbl, c_derived_tbl *actbl) |
| 359 | { |
| 360 | register int temp, temp2; |
| 361 | register int nbits; |
| 362 | register int k, r, i; |
| 363 | |
| 364 | /* Encode the DC coefficient difference per section F.1.2.1 */ |
| 365 | |
| 366 | temp = temp2 = block[0] - last_dc_val; |
| 367 | |
| 368 | if (temp < 0) { |
| 369 | temp = -temp; /* temp is abs value of input */ |
| 370 | /* For a negative input, want temp2 = bitwise complement of abs(input) */ |
| 371 | /* This code assumes we are on a two's complement machine */ |
| 372 | temp2--; |
| 373 | } |
| 374 | |
| 375 | /* Find the number of bits needed for the magnitude of the coefficient */ |
| 376 | nbits = 0; |
| 377 | while (temp) { |
| 378 | nbits++; |
| 379 | temp >>= 1; |
| 380 | } |
| 381 | /* Check for out-of-range coefficient values. |
| 382 | * Since we're encoding a difference, the range limit is twice as much. |
| 383 | */ |
| 384 | if (nbits > MAX_COEF_BITS+1) |
| 385 | ERREXIT(state->cinfo, JERR_BAD_DCT_COEF); |
| 386 | |
| 387 | /* Emit the Huffman-coded symbol for the number of bits */ |
| 388 | if (! emit_bits(state, dctbl->ehufco[nbits], dctbl->ehufsi[nbits])) |
| 389 | return FALSE; |
| 390 | |
| 391 | /* Emit that number of bits of the value, if positive, */ |
| 392 | /* or the complement of its magnitude, if negative. */ |
| 393 | if (nbits) /* emit_bits rejects calls with size 0 */ |
| 394 | if (! emit_bits(state, (unsigned int) temp2, nbits)) |
| 395 | return FALSE; |
| 396 | |
| 397 | /* Encode the AC coefficients per section F.1.2.2 */ |
| 398 | |
| 399 | r = 0; /* r = run length of zeros */ |
| 400 | |
| 401 | for (k = 1; k < DCTSIZE2; k++) { |
| 402 | if ((temp = block[jpeg_natural_order[k]]) == 0) { |
| 403 | r++; |
| 404 | } else { |
| 405 | /* if run length > 15, must emit special run-length-16 codes (0xF0) */ |
| 406 | while (r > 15) { |
| 407 | if (! emit_bits(state, actbl->ehufco[0xF0], actbl->ehufsi[0xF0])) |
| 408 | return FALSE; |
| 409 | r -= 16; |
| 410 | } |
| 411 | |
| 412 | temp2 = temp; |
| 413 | if (temp < 0) { |
| 414 | temp = -temp; /* temp is abs value of input */ |
| 415 | /* This code assumes we are on a two's complement machine */ |
| 416 | temp2--; |
| 417 | } |
| 418 | |
| 419 | /* Find the number of bits needed for the magnitude of the coefficient */ |
| 420 | nbits = 1; /* there must be at least one 1 bit */ |
| 421 | while ((temp >>= 1)) |
| 422 | nbits++; |
| 423 | /* Check for out-of-range coefficient values */ |
| 424 | if (nbits > MAX_COEF_BITS) |
| 425 | ERREXIT(state->cinfo, JERR_BAD_DCT_COEF); |
| 426 | |
| 427 | /* Emit Huffman symbol for run length / number of bits */ |
| 428 | i = (r << 4) + nbits; |
| 429 | if (! emit_bits(state, actbl->ehufco[i], actbl->ehufsi[i])) |
| 430 | return FALSE; |
| 431 | |
| 432 | /* Emit that number of bits of the value, if positive, */ |
| 433 | /* or the complement of its magnitude, if negative. */ |
| 434 | if (! emit_bits(state, (unsigned int) temp2, nbits)) |
| 435 | return FALSE; |
| 436 | |
| 437 | r = 0; |
| 438 | } |
| 439 | } |
| 440 | |
| 441 | /* If the last coef(s) were zero, emit an end-of-block code */ |
| 442 | if (r > 0) |
| 443 | if (! emit_bits(state, actbl->ehufco[0], actbl->ehufsi[0])) |
| 444 | return FALSE; |
| 445 | |
| 446 | return TRUE; |
| 447 | } |
| 448 | |
| 449 | |
| 450 | /* |
| 451 | * Emit a restart marker & resynchronize predictions. |
| 452 | */ |
| 453 | |
| 454 | LOCAL(boolean) |
| 455 | emit_restart (working_state * state, int restart_num) |
| 456 | { |
| 457 | int ci; |
| 458 | |
| 459 | if (! flush_bits(state)) |
| 460 | return FALSE; |
| 461 | |
| 462 | emit_byte(state, 0xFF, return FALSE); |
| 463 | emit_byte(state, JPEG_RST0 + restart_num, return FALSE); |
| 464 | |
| 465 | /* Re-initialize DC predictions to 0 */ |
| 466 | for (ci = 0; ci < state->cinfo->comps_in_scan; ci++) |
| 467 | state->cur.last_dc_val[ci] = 0; |
| 468 | |
| 469 | /* The restart counter is not updated until we successfully write the MCU. */ |
| 470 | |
| 471 | return TRUE; |
| 472 | } |
| 473 | |
| 474 | |
| 475 | /* |
| 476 | * Encode and output one MCU's worth of Huffman-compressed coefficients. |
| 477 | */ |
| 478 | |
| 479 | METHODDEF(boolean) |
| 480 | encode_mcu_huff (j_compress_ptr cinfo, JBLOCKROW *MCU_data) |
| 481 | { |
| 482 | huff_entropy_ptr entropy = (huff_entropy_ptr) cinfo->entropy; |
| 483 | working_state state; |
| 484 | int blkn, ci; |
| 485 | jpeg_component_info * compptr; |
| 486 | |
| 487 | /* Load up working state */ |
| 488 | state.next_output_byte = cinfo->dest->next_output_byte; |
| 489 | state.free_in_buffer = cinfo->dest->free_in_buffer; |
| 490 | ASSIGN_STATE(state.cur, entropy->saved); |
| 491 | state.cinfo = cinfo; |
| 492 | |
| 493 | /* Emit restart marker if needed */ |
| 494 | if (cinfo->restart_interval) { |
| 495 | if (entropy->restarts_to_go == 0) |
| 496 | if (! emit_restart(&state, entropy->next_restart_num)) |
| 497 | return FALSE; |
| 498 | } |
| 499 | |
| 500 | /* Encode the MCU data blocks */ |
| 501 | for (blkn = 0; blkn < cinfo->blocks_in_MCU; blkn++) { |
| 502 | ci = cinfo->MCU_membership[blkn]; |
| 503 | compptr = cinfo->cur_comp_info[ci]; |
| 504 | if (! encode_one_block(&state, |
| 505 | MCU_data[blkn][0], state.cur.last_dc_val[ci], |
| 506 | entropy->dc_derived_tbls[compptr->dc_tbl_no], |
| 507 | entropy->ac_derived_tbls[compptr->ac_tbl_no])) |
| 508 | return FALSE; |
| 509 | /* Update last_dc_val */ |
| 510 | state.cur.last_dc_val[ci] = MCU_data[blkn][0][0]; |
| 511 | } |
| 512 | |
| 513 | /* Completed MCU, so update state */ |
| 514 | cinfo->dest->next_output_byte = state.next_output_byte; |
| 515 | cinfo->dest->free_in_buffer = state.free_in_buffer; |
| 516 | ASSIGN_STATE(entropy->saved, state.cur); |
| 517 | |
| 518 | /* Update restart-interval state too */ |
| 519 | if (cinfo->restart_interval) { |
| 520 | if (entropy->restarts_to_go == 0) { |
| 521 | entropy->restarts_to_go = cinfo->restart_interval; |
| 522 | entropy->next_restart_num++; |
| 523 | entropy->next_restart_num &= 7; |
| 524 | } |
| 525 | entropy->restarts_to_go--; |
| 526 | } |
| 527 | |
| 528 | return TRUE; |
| 529 | } |
| 530 | |
| 531 | |
| 532 | /* |
| 533 | * Finish up at the end of a Huffman-compressed scan. |
| 534 | */ |
| 535 | |
| 536 | METHODDEF(void) |
| 537 | finish_pass_huff (j_compress_ptr cinfo) |
| 538 | { |
| 539 | huff_entropy_ptr entropy = (huff_entropy_ptr) cinfo->entropy; |
| 540 | working_state state; |
| 541 | |
| 542 | /* Load up working state ... flush_bits needs it */ |
| 543 | state.next_output_byte = cinfo->dest->next_output_byte; |
| 544 | state.free_in_buffer = cinfo->dest->free_in_buffer; |
| 545 | ASSIGN_STATE(state.cur, entropy->saved); |
| 546 | state.cinfo = cinfo; |
| 547 | |
| 548 | /* Flush out the last data */ |
| 549 | if (! flush_bits(&state)) |
| 550 | ERREXIT(cinfo, JERR_CANT_SUSPEND); |
| 551 | |
| 552 | /* Update state */ |
| 553 | cinfo->dest->next_output_byte = state.next_output_byte; |
| 554 | cinfo->dest->free_in_buffer = state.free_in_buffer; |
| 555 | ASSIGN_STATE(entropy->saved, state.cur); |
| 556 | } |
| 557 | |
| 558 | |
| 559 | /* |
| 560 | * Huffman coding optimization. |
| 561 | * |
| 562 | * We first scan the supplied data and count the number of uses of each symbol |
| 563 | * that is to be Huffman-coded. (This process MUST agree with the code above.) |
| 564 | * Then we build a Huffman coding tree for the observed counts. |
| 565 | * Symbols which are not needed at all for the particular image are not |
| 566 | * assigned any code, which saves space in the DHT marker as well as in |
| 567 | * the compressed data. |
| 568 | */ |
| 569 | |
| 570 | #ifdef ENTROPY_OPT_SUPPORTED |
| 571 | |
| 572 | |
| 573 | /* Process a single block's worth of coefficients */ |
| 574 | |
| 575 | LOCAL(void) |
| 576 | htest_one_block (j_compress_ptr cinfo, JCOEFPTR block, int last_dc_val, |
| 577 | long dc_counts[], long ac_counts[]) |
| 578 | { |
| 579 | register int temp; |
| 580 | register int nbits; |
| 581 | register int k, r; |
| 582 | |
| 583 | /* Encode the DC coefficient difference per section F.1.2.1 */ |
| 584 | |
| 585 | temp = block[0] - last_dc_val; |
| 586 | if (temp < 0) |
| 587 | temp = -temp; |
| 588 | |
| 589 | /* Find the number of bits needed for the magnitude of the coefficient */ |
| 590 | nbits = 0; |
| 591 | while (temp) { |
| 592 | nbits++; |
| 593 | temp >>= 1; |
| 594 | } |
| 595 | /* Check for out-of-range coefficient values. |
| 596 | * Since we're encoding a difference, the range limit is twice as much. |
| 597 | */ |
| 598 | if (nbits > MAX_COEF_BITS+1) |
| 599 | ERREXIT(cinfo, JERR_BAD_DCT_COEF); |
| 600 | |
| 601 | /* Count the Huffman symbol for the number of bits */ |
| 602 | dc_counts[nbits]++; |
| 603 | |
| 604 | /* Encode the AC coefficients per section F.1.2.2 */ |
| 605 | |
| 606 | r = 0; /* r = run length of zeros */ |
| 607 | |
| 608 | for (k = 1; k < DCTSIZE2; k++) { |
| 609 | if ((temp = block[jpeg_natural_order[k]]) == 0) { |
| 610 | r++; |
| 611 | } else { |
| 612 | /* if run length > 15, must emit special run-length-16 codes (0xF0) */ |
| 613 | while (r > 15) { |
| 614 | ac_counts[0xF0]++; |
| 615 | r -= 16; |
| 616 | } |
| 617 | |
| 618 | /* Find the number of bits needed for the magnitude of the coefficient */ |
| 619 | if (temp < 0) |
| 620 | temp = -temp; |
| 621 | |
| 622 | /* Find the number of bits needed for the magnitude of the coefficient */ |
| 623 | nbits = 1; /* there must be at least one 1 bit */ |
| 624 | while ((temp >>= 1)) |
| 625 | nbits++; |
| 626 | /* Check for out-of-range coefficient values */ |
| 627 | if (nbits > MAX_COEF_BITS) |
| 628 | ERREXIT(cinfo, JERR_BAD_DCT_COEF); |
| 629 | |
| 630 | /* Count Huffman symbol for run length / number of bits */ |
| 631 | ac_counts[(r << 4) + nbits]++; |
| 632 | |
| 633 | r = 0; |
| 634 | } |
| 635 | } |
| 636 | |
| 637 | /* If the last coef(s) were zero, emit an end-of-block code */ |
| 638 | if (r > 0) |
| 639 | ac_counts[0]++; |
| 640 | } |
| 641 | |
| 642 | |
| 643 | /* |
| 644 | * Trial-encode one MCU's worth of Huffman-compressed coefficients. |
| 645 | * No data is actually output, so no suspension return is possible. |
| 646 | */ |
| 647 | |
| 648 | METHODDEF(boolean) |
| 649 | encode_mcu_gather (j_compress_ptr cinfo, JBLOCKROW *MCU_data) |
| 650 | { |
| 651 | huff_entropy_ptr entropy = (huff_entropy_ptr) cinfo->entropy; |
| 652 | int blkn, ci; |
| 653 | jpeg_component_info * compptr; |
| 654 | |
| 655 | /* Take care of restart intervals if needed */ |
| 656 | if (cinfo->restart_interval) { |
| 657 | if (entropy->restarts_to_go == 0) { |
| 658 | /* Re-initialize DC predictions to 0 */ |
| 659 | for (ci = 0; ci < cinfo->comps_in_scan; ci++) |
| 660 | entropy->saved.last_dc_val[ci] = 0; |
| 661 | /* Update restart state */ |
| 662 | entropy->restarts_to_go = cinfo->restart_interval; |
| 663 | } |
| 664 | entropy->restarts_to_go--; |
| 665 | } |
| 666 | |
| 667 | for (blkn = 0; blkn < cinfo->blocks_in_MCU; blkn++) { |
| 668 | ci = cinfo->MCU_membership[blkn]; |
| 669 | compptr = cinfo->cur_comp_info[ci]; |
| 670 | htest_one_block(cinfo, MCU_data[blkn][0], entropy->saved.last_dc_val[ci], |
| 671 | entropy->dc_count_ptrs[compptr->dc_tbl_no], |
| 672 | entropy->ac_count_ptrs[compptr->ac_tbl_no]); |
| 673 | entropy->saved.last_dc_val[ci] = MCU_data[blkn][0][0]; |
| 674 | } |
| 675 | |
| 676 | return TRUE; |
| 677 | } |
| 678 | |
| 679 | |
| 680 | /* |
| 681 | * Generate the best Huffman code table for the given counts, fill htbl. |
| 682 | * Note this is also used by jcphuff.c. |
| 683 | * |
| 684 | * The JPEG standard requires that no symbol be assigned a codeword of all |
| 685 | * one bits (so that padding bits added at the end of a compressed segment |
| 686 | * can't look like a valid code). Because of the canonical ordering of |
| 687 | * codewords, this just means that there must be an unused slot in the |
| 688 | * longest codeword length category. Section K.2 of the JPEG spec suggests |
| 689 | * reserving such a slot by pretending that symbol 256 is a valid symbol |
| 690 | * with count 1. In theory that's not optimal; giving it count zero but |
| 691 | * including it in the symbol set anyway should give a better Huffman code. |
| 692 | * But the theoretically better code actually seems to come out worse in |
| 693 | * practice, because it produces more all-ones bytes (which incur stuffed |
| 694 | * zero bytes in the final file). In any case the difference is tiny. |
| 695 | * |
| 696 | * The JPEG standard requires Huffman codes to be no more than 16 bits long. |
| 697 | * If some symbols have a very small but nonzero probability, the Huffman tree |
| 698 | * must be adjusted to meet the code length restriction. We currently use |
| 699 | * the adjustment method suggested in JPEG section K.2. This method is *not* |
| 700 | * optimal; it may not choose the best possible limited-length code. But |
| 701 | * typically only very-low-frequency symbols will be given less-than-optimal |
| 702 | * lengths, so the code is almost optimal. Experimental comparisons against |
| 703 | * an optimal limited-length-code algorithm indicate that the difference is |
| 704 | * microscopic --- usually less than a hundredth of a percent of total size. |
| 705 | * So the extra complexity of an optimal algorithm doesn't seem worthwhile. |
| 706 | */ |
| 707 | |
| 708 | GLOBAL(void) |
| 709 | jpeg_gen_optimal_table (j_compress_ptr cinfo, JHUFF_TBL * htbl, long freq[]) |
| 710 | { |
| 711 | #define MAX_CLEN 32 /* assumed maximum initial code length */ |
| 712 | UINT8 bits[MAX_CLEN+1]; /* bits[k] = # of symbols with code length k */ |
| 713 | int codesize[257]; /* codesize[k] = code length of symbol k */ |
| 714 | int others[257]; /* next symbol in current branch of tree */ |
| 715 | int c1, c2; |
| 716 | int p, i, j; |
| 717 | long v; |
| 718 | |
| 719 | /* This algorithm is explained in section K.2 of the JPEG standard */ |
| 720 | |
| 721 | MEMZERO(bits, SIZEOF(bits)); |
| 722 | MEMZERO(codesize, SIZEOF(codesize)); |
| 723 | for (i = 0; i < 257; i++) |
| 724 | others[i] = -1; /* init links to empty */ |
| 725 | |
| 726 | freq[256] = 1; /* make sure 256 has a nonzero count */ |
| 727 | /* Including the pseudo-symbol 256 in the Huffman procedure guarantees |
| 728 | * that no real symbol is given code-value of all ones, because 256 |
| 729 | * will be placed last in the largest codeword category. |
| 730 | */ |
| 731 | |
| 732 | /* Huffman's basic algorithm to assign optimal code lengths to symbols */ |
| 733 | |
| 734 | for (;;) { |
| 735 | /* Find the smallest nonzero frequency, set c1 = its symbol */ |
| 736 | /* In case of ties, take the larger symbol number */ |
| 737 | c1 = -1; |
| 738 | v = 1000000000L; |
| 739 | for (i = 0; i <= 256; i++) { |
| 740 | if (freq[i] && freq[i] <= v) { |
| 741 | v = freq[i]; |
| 742 | c1 = i; |
| 743 | } |
| 744 | } |
| 745 | |
| 746 | /* Find the next smallest nonzero frequency, set c2 = its symbol */ |
| 747 | /* In case of ties, take the larger symbol number */ |
| 748 | c2 = -1; |
| 749 | v = 1000000000L; |
| 750 | for (i = 0; i <= 256; i++) { |
| 751 | if (freq[i] && freq[i] <= v && i != c1) { |
| 752 | v = freq[i]; |
| 753 | c2 = i; |
| 754 | } |
| 755 | } |
| 756 | |
| 757 | /* Done if we've merged everything into one frequency */ |
| 758 | if (c2 < 0) |
| 759 | break; |
| 760 | |
| 761 | /* Else merge the two counts/trees */ |
| 762 | freq[c1] += freq[c2]; |
| 763 | freq[c2] = 0; |
| 764 | |
| 765 | /* Increment the codesize of everything in c1's tree branch */ |
| 766 | codesize[c1]++; |
| 767 | while (others[c1] >= 0) { |
| 768 | c1 = others[c1]; |
| 769 | codesize[c1]++; |
| 770 | } |
| 771 | |
| 772 | others[c1] = c2; /* chain c2 onto c1's tree branch */ |
| 773 | |
| 774 | /* Increment the codesize of everything in c2's tree branch */ |
| 775 | codesize[c2]++; |
| 776 | while (others[c2] >= 0) { |
| 777 | c2 = others[c2]; |
| 778 | codesize[c2]++; |
| 779 | } |
| 780 | } |
| 781 | |
| 782 | /* Now count the number of symbols of each code length */ |
| 783 | for (i = 0; i <= 256; i++) { |
| 784 | if (codesize[i]) { |
| 785 | /* The JPEG standard seems to think that this can't happen, */ |
| 786 | /* but I'm paranoid... */ |
| 787 | if (codesize[i] > MAX_CLEN) |
| 788 | ERREXIT(cinfo, JERR_HUFF_CLEN_OVERFLOW); |
| 789 | |
| 790 | bits[codesize[i]]++; |
| 791 | } |
| 792 | } |
| 793 | |
| 794 | /* JPEG doesn't allow symbols with code lengths over 16 bits, so if the pure |
| 795 | * Huffman procedure assigned any such lengths, we must adjust the coding. |
| 796 | * Here is what the JPEG spec says about how this next bit works: |
| 797 | * Since symbols are paired for the longest Huffman code, the symbols are |
| 798 | * removed from this length category two at a time. The prefix for the pair |
| 799 | * (which is one bit shorter) is allocated to one of the pair; then, |
| 800 | * skipping the BITS entry for that prefix length, a code word from the next |
| 801 | * shortest nonzero BITS entry is converted into a prefix for two code words |
| 802 | * one bit longer. |
| 803 | */ |
| 804 | |
| 805 | for (i = MAX_CLEN; i > 16; i--) { |
| 806 | while (bits[i] > 0) { |
| 807 | j = i - 2; /* find length of new prefix to be used */ |
| 808 | while (bits[j] == 0) |
| 809 | j--; |
| 810 | |
| 811 | bits[i] -= 2; /* remove two symbols */ |
| 812 | bits[i-1]++; /* one goes in this length */ |
| 813 | bits[j+1] += 2; /* two new symbols in this length */ |
| 814 | bits[j]--; /* symbol of this length is now a prefix */ |
| 815 | } |
| 816 | } |
| 817 | |
| 818 | /* Remove the count for the pseudo-symbol 256 from the largest codelength */ |
| 819 | while (bits[i] == 0) /* find largest codelength still in use */ |
| 820 | i--; |
| 821 | bits[i]--; |
| 822 | |
| 823 | /* Return final symbol counts (only for lengths 0..16) */ |
| 824 | MEMCOPY(htbl->bits, bits, SIZEOF(htbl->bits)); |
| 825 | |
| 826 | /* Return a list of the symbols sorted by code length */ |
| 827 | /* It's not real clear to me why we don't need to consider the codelength |
| 828 | * changes made above, but the JPEG spec seems to think this works. |
| 829 | */ |
| 830 | p = 0; |
| 831 | for (i = 1; i <= MAX_CLEN; i++) { |
| 832 | for (j = 0; j <= 255; j++) { |
| 833 | if (codesize[j] == i) { |
| 834 | htbl->huffval[p] = (UINT8) j; |
| 835 | p++; |
| 836 | } |
| 837 | } |
| 838 | } |
| 839 | |
| 840 | /* Set sent_table FALSE so updated table will be written to JPEG file. */ |
| 841 | htbl->sent_table = FALSE; |
| 842 | } |
| 843 | |
| 844 | |
| 845 | /* |
| 846 | * Finish up a statistics-gathering pass and create the new Huffman tables. |
| 847 | */ |
| 848 | |
| 849 | METHODDEF(void) |
| 850 | finish_pass_gather (j_compress_ptr cinfo) |
| 851 | { |
| 852 | huff_entropy_ptr entropy = (huff_entropy_ptr) cinfo->entropy; |
| 853 | int ci, dctbl, actbl; |
| 854 | jpeg_component_info * compptr; |
| 855 | JHUFF_TBL **htblptr; |
| 856 | boolean did_dc[NUM_HUFF_TBLS]; |
| 857 | boolean did_ac[NUM_HUFF_TBLS]; |
| 858 | |
| 859 | /* It's important not to apply jpeg_gen_optimal_table more than once |
| 860 | * per table, because it clobbers the input frequency counts! |
| 861 | */ |
| 862 | MEMZERO(did_dc, SIZEOF(did_dc)); |
| 863 | MEMZERO(did_ac, SIZEOF(did_ac)); |
| 864 | |
| 865 | for (ci = 0; ci < cinfo->comps_in_scan; ci++) { |
| 866 | compptr = cinfo->cur_comp_info[ci]; |
| 867 | dctbl = compptr->dc_tbl_no; |
| 868 | actbl = compptr->ac_tbl_no; |
| 869 | if (! did_dc[dctbl]) { |
| 870 | htblptr = & cinfo->dc_huff_tbl_ptrs[dctbl]; |
| 871 | if (*htblptr == NULL) |
| 872 | *htblptr = jpeg_alloc_huff_table((j_common_ptr) cinfo); |
| 873 | jpeg_gen_optimal_table(cinfo, *htblptr, entropy->dc_count_ptrs[dctbl]); |
| 874 | did_dc[dctbl] = TRUE; |
| 875 | } |
| 876 | if (! did_ac[actbl]) { |
| 877 | htblptr = & cinfo->ac_huff_tbl_ptrs[actbl]; |
| 878 | if (*htblptr == NULL) |
| 879 | *htblptr = jpeg_alloc_huff_table((j_common_ptr) cinfo); |
| 880 | jpeg_gen_optimal_table(cinfo, *htblptr, entropy->ac_count_ptrs[actbl]); |
| 881 | did_ac[actbl] = TRUE; |
| 882 | } |
| 883 | } |
| 884 | } |
| 885 | |
| 886 | |
| 887 | #endif /* ENTROPY_OPT_SUPPORTED */ |
| 888 | |
| 889 | |
| 890 | /* |
| 891 | * Module initialization routine for Huffman entropy encoding. |
| 892 | */ |
| 893 | |
| 894 | GLOBAL(void) |
| 895 | jinit_huff_encoder (j_compress_ptr cinfo) |
| 896 | { |
| 897 | huff_entropy_ptr entropy; |
| 898 | int i; |
| 899 | |
| 900 | entropy = (huff_entropy_ptr) |
| 901 | (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE, |
| 902 | SIZEOF(huff_entropy_encoder)); |
| 903 | cinfo->entropy = (struct jpeg_entropy_encoder *) entropy; |
| 904 | entropy->pub.start_pass = start_pass_huff; |
| 905 | |
| 906 | /* Mark tables unallocated */ |
| 907 | for (i = 0; i < NUM_HUFF_TBLS; i++) { |
| 908 | entropy->dc_derived_tbls[i] = entropy->ac_derived_tbls[i] = NULL; |
| 909 | #ifdef ENTROPY_OPT_SUPPORTED |
| 910 | entropy->dc_count_ptrs[i] = entropy->ac_count_ptrs[i] = NULL; |
| 911 | #endif |
| 912 | } |
| 913 | } |