1/* 2 * jchuff.c 3 * 4 * This file was part of the Independent JPEG Group's software: 5 * Copyright (C) 1991-1997, Thomas G. Lane. 6 * libjpeg-turbo Modifications: 7 * Copyright (C) 2009-2011, 2014-2016, D. R. Commander. 8 * Copyright (C) 2015, Matthieu Darbois. 9 * For conditions of distribution and use, see the accompanying README.ijg 10 * 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 "jsimd.h" 25#include "jconfigint.h" 26#include <limits.h> 27 28/* 29 * NOTE: If USE_CLZ_INTRINSIC is defined, then clz/bsr instructions will be 30 * used for bit counting rather than the lookup table. This will reduce the 31 * memory footprint by 64k, which is important for some mobile applications 32 * that create many isolated instances of libjpeg-turbo (web browsers, for 33 * instance.) This may improve performance on some mobile platforms as well. 34 * This feature is enabled by default only on ARM processors, because some x86 35 * chips have a slow implementation of bsr, and the use of clz/bsr cannot be 36 * shown to have a significant performance impact even on the x86 chips that 37 * have a fast implementation of it. When building for ARMv6, you can 38 * explicitly disable the use of clz/bsr by adding -mthumb to the compiler 39 * flags (this defines __thumb__). 40 */ 41 42/* NOTE: Both GCC and Clang define __GNUC__ */ 43#if defined __GNUC__ && (defined __arm__ || defined __aarch64__) 44#if !defined __thumb__ || defined __thumb2__ 45#define USE_CLZ_INTRINSIC 46#endif 47#endif 48 49#ifdef USE_CLZ_INTRINSIC 50#define JPEG_NBITS_NONZERO(x) (32 - __builtin_clz(x)) 51#define JPEG_NBITS(x) (x ? JPEG_NBITS_NONZERO(x) : 0) 52#else 53#include "jpeg_nbits_table.h" 54#define JPEG_NBITS(x) (jpeg_nbits_table[x]) 55#define JPEG_NBITS_NONZERO(x) JPEG_NBITS(x) 56#endif 57 58#ifndef min 59 #define min(a,b) ((a)<(b)?(a):(b)) 60#endif 61 62 63/* Expanded entropy encoder object for Huffman encoding. 64 * 65 * The savable_state subrecord contains fields that change within an MCU, 66 * but must not be updated permanently until we complete the MCU. 67 */ 68 69typedef struct { 70 size_t put_buffer; /* current bit-accumulation buffer */ 71 int put_bits; /* # of bits now in it */ 72 int last_dc_val[MAX_COMPS_IN_SCAN]; /* last DC coef for each component */ 73} savable_state; 74 75/* This macro is to work around compilers with missing or broken 76 * structure assignment. You'll need to fix this code if you have 77 * such a compiler and you change MAX_COMPS_IN_SCAN. 78 */ 79 80#ifndef NO_STRUCT_ASSIGN 81#define ASSIGN_STATE(dest,src) ((dest) = (src)) 82#else 83#if MAX_COMPS_IN_SCAN == 4 84#define ASSIGN_STATE(dest,src) \ 85 ((dest).put_buffer = (src).put_buffer, \ 86 (dest).put_bits = (src).put_bits, \ 87 (dest).last_dc_val[0] = (src).last_dc_val[0], \ 88 (dest).last_dc_val[1] = (src).last_dc_val[1], \ 89 (dest).last_dc_val[2] = (src).last_dc_val[2], \ 90 (dest).last_dc_val[3] = (src).last_dc_val[3]) 91#endif 92#endif 93 94 95typedef struct { 96 struct jpeg_entropy_encoder pub; /* public fields */ 97 98 savable_state saved; /* Bit buffer & DC state at start of MCU */ 99 100 /* These fields are NOT loaded into local working state. */ 101 unsigned int restarts_to_go; /* MCUs left in this restart interval */ 102 int next_restart_num; /* next restart number to write (0-7) */ 103 104 /* Pointers to derived tables (these workspaces have image lifespan) */ 105 c_derived_tbl *dc_derived_tbls[NUM_HUFF_TBLS]; 106 c_derived_tbl *ac_derived_tbls[NUM_HUFF_TBLS]; 107 108#ifdef ENTROPY_OPT_SUPPORTED /* Statistics tables for optimization */ 109 long *dc_count_ptrs[NUM_HUFF_TBLS]; 110 long *ac_count_ptrs[NUM_HUFF_TBLS]; 111#endif 112 113 int simd; 114} huff_entropy_encoder; 115 116typedef huff_entropy_encoder *huff_entropy_ptr; 117 118/* Working state while writing an MCU. 119 * This struct contains all the fields that are needed by subroutines. 120 */ 121 122typedef struct { 123 JOCTET *next_output_byte; /* => next byte to write in buffer */ 124 size_t free_in_buffer; /* # of byte spaces remaining in buffer */ 125 savable_state cur; /* Current bit buffer & DC state */ 126 j_compress_ptr cinfo; /* dump_buffer needs access to this */ 127} working_state; 128 129 130/* Forward declarations */ 131METHODDEF(boolean) encode_mcu_huff (j_compress_ptr cinfo, JBLOCKROW *MCU_data); 132METHODDEF(void) finish_pass_huff (j_compress_ptr cinfo); 133#ifdef ENTROPY_OPT_SUPPORTED 134METHODDEF(boolean) encode_mcu_gather (j_compress_ptr cinfo, 135 JBLOCKROW *MCU_data); 136METHODDEF(void) finish_pass_gather (j_compress_ptr cinfo); 137#endif 138 139 140/* 141 * Initialize for a Huffman-compressed scan. 142 * If gather_statistics is TRUE, we do not output anything during the scan, 143 * just count the Huffman symbols used and generate Huffman code tables. 144 */ 145 146METHODDEF(void) 147start_pass_huff (j_compress_ptr cinfo, boolean gather_statistics) 148{ 149 huff_entropy_ptr entropy = (huff_entropy_ptr) cinfo->entropy; 150 int ci, dctbl, actbl; 151 jpeg_component_info *compptr; 152 153 if (gather_statistics) { 154#ifdef ENTROPY_OPT_SUPPORTED 155 entropy->pub.encode_mcu = encode_mcu_gather; 156 entropy->pub.finish_pass = finish_pass_gather; 157#else 158 ERREXIT(cinfo, JERR_NOT_COMPILED); 159#endif 160 } else { 161 entropy->pub.encode_mcu = encode_mcu_huff; 162 entropy->pub.finish_pass = finish_pass_huff; 163 } 164 165 entropy->simd = jsimd_can_huff_encode_one_block(); 166 167 for (ci = 0; ci < cinfo->comps_in_scan; ci++) { 168 compptr = cinfo->cur_comp_info[ci]; 169 dctbl = compptr->dc_tbl_no; 170 actbl = compptr->ac_tbl_no; 171 if (gather_statistics) { 172#ifdef ENTROPY_OPT_SUPPORTED 173 /* Check for invalid table indexes */ 174 /* (make_c_derived_tbl does this in the other path) */ 175 if (dctbl < 0 || dctbl >= NUM_HUFF_TBLS) 176 ERREXIT1(cinfo, JERR_NO_HUFF_TABLE, dctbl); 177 if (actbl < 0 || actbl >= NUM_HUFF_TBLS) 178 ERREXIT1(cinfo, JERR_NO_HUFF_TABLE, actbl); 179 /* Allocate and zero the statistics tables */ 180 /* Note that jpeg_gen_optimal_table expects 257 entries in each table! */ 181 if (entropy->dc_count_ptrs[dctbl] == NULL) 182 entropy->dc_count_ptrs[dctbl] = (long *) 183 (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE, 184 257 * sizeof(long)); 185 MEMZERO(entropy->dc_count_ptrs[dctbl], 257 * sizeof(long)); 186 if (entropy->ac_count_ptrs[actbl] == NULL) 187 entropy->ac_count_ptrs[actbl] = (long *) 188 (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE, 189 257 * sizeof(long)); 190 MEMZERO(entropy->ac_count_ptrs[actbl], 257 * sizeof(long)); 191#endif 192 } else { 193 /* Compute derived values for Huffman tables */ 194 /* We may do this more than once for a table, but it's not expensive */ 195 jpeg_make_c_derived_tbl(cinfo, TRUE, dctbl, 196 & entropy->dc_derived_tbls[dctbl]); 197 jpeg_make_c_derived_tbl(cinfo, FALSE, actbl, 198 & entropy->ac_derived_tbls[actbl]); 199 } 200 /* Initialize DC predictions to 0 */ 201 entropy->saved.last_dc_val[ci] = 0; 202 } 203 204 /* Initialize bit buffer to empty */ 205 entropy->saved.put_buffer = 0; 206 entropy->saved.put_bits = 0; 207 208 /* Initialize restart stuff */ 209 entropy->restarts_to_go = cinfo->restart_interval; 210 entropy->next_restart_num = 0; 211} 212 213 214/* 215 * Compute the derived values for a Huffman table. 216 * This routine also performs some validation checks on the table. 217 * 218 * Note this is also used by jcphuff.c. 219 */ 220 221GLOBAL(void) 222jpeg_make_c_derived_tbl (j_compress_ptr cinfo, boolean isDC, int tblno, 223 c_derived_tbl **pdtbl) 224{ 225 JHUFF_TBL *htbl; 226 c_derived_tbl *dtbl; 227 int p, i, l, lastp, si, maxsymbol; 228 char huffsize[257]; 229 unsigned int huffcode[257]; 230 unsigned int code; 231 232 /* Note that huffsize[] and huffcode[] are filled in code-length order, 233 * paralleling the order of the symbols themselves in htbl->huffval[]. 234 */ 235 236 /* Find the input Huffman table */ 237 if (tblno < 0 || tblno >= NUM_HUFF_TBLS) 238 ERREXIT1(cinfo, JERR_NO_HUFF_TABLE, tblno); 239 htbl = 240 isDC ? cinfo->dc_huff_tbl_ptrs[tblno] : cinfo->ac_huff_tbl_ptrs[tblno]; 241 if (htbl == NULL) 242 ERREXIT1(cinfo, JERR_NO_HUFF_TABLE, tblno); 243 244 /* Allocate a workspace if we haven't already done so. */ 245 if (*pdtbl == NULL) 246 *pdtbl = (c_derived_tbl *) 247 (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE, 248 sizeof(c_derived_tbl)); 249 dtbl = *pdtbl; 250 251 /* Figure C.1: make table of Huffman code length for each symbol */ 252 253 p = 0; 254 for (l = 1; l <= 16; l++) { 255 i = (int) htbl->bits[l]; 256 if (i < 0 || p + i > 256) /* protect against table overrun */ 257 ERREXIT(cinfo, JERR_BAD_HUFF_TABLE); 258 while (i--) 259 huffsize[p++] = (char) l; 260 } 261 huffsize[p] = 0; 262 lastp = p; 263 264 /* Figure C.2: generate the codes themselves */ 265 /* We also validate that the counts represent a legal Huffman code tree. */ 266 267 code = 0; 268 si = huffsize[0]; 269 p = 0; 270 while (huffsize[p]) { 271 while (((int) huffsize[p]) == si) { 272 huffcode[p++] = code; 273 code++; 274 } 275 /* code is now 1 more than the last code used for codelength si; but 276 * it must still fit in si bits, since no code is allowed to be all ones. 277 */ 278 if (((JLONG) code) >= (((JLONG) 1) << si)) 279 ERREXIT(cinfo, JERR_BAD_HUFF_TABLE); 280 code <<= 1; 281 si++; 282 } 283 284 /* Figure C.3: generate encoding tables */ 285 /* These are code and size indexed by symbol value */ 286 287 /* Set all codeless symbols to have code length 0; 288 * this lets us detect duplicate VAL entries here, and later 289 * allows emit_bits to detect any attempt to emit such symbols. 290 */ 291 MEMZERO(dtbl->ehufsi, sizeof(dtbl->ehufsi)); 292 293 /* This is also a convenient place to check for out-of-range 294 * and duplicated VAL entries. We allow 0..255 for AC symbols 295 * but only 0..15 for DC. (We could constrain them further 296 * based on data depth and mode, but this seems enough.) 297 */ 298 maxsymbol = isDC ? 15 : 255; 299 300 for (p = 0; p < lastp; p++) { 301 i = htbl->huffval[p]; 302 if (i < 0 || i > maxsymbol || dtbl->ehufsi[i]) 303 ERREXIT(cinfo, JERR_BAD_HUFF_TABLE); 304 dtbl->ehufco[i] = huffcode[p]; 305 dtbl->ehufsi[i] = huffsize[p]; 306 } 307} 308 309 310/* Outputting bytes to the file */ 311 312/* Emit a byte, taking 'action' if must suspend. */ 313#define emit_byte(state,val,action) \ 314 { *(state)->next_output_byte++ = (JOCTET) (val); \ 315 if (--(state)->free_in_buffer == 0) \ 316 if (! dump_buffer(state)) \ 317 { action; } } 318 319 320LOCAL(boolean) 321dump_buffer (working_state *state) 322/* Empty the output buffer; return TRUE if successful, FALSE if must suspend */ 323{ 324 struct jpeg_destination_mgr *dest = state->cinfo->dest; 325 326 if (! (*dest->empty_output_buffer) (state->cinfo)) 327 return FALSE; 328 /* After a successful buffer dump, must reset buffer pointers */ 329 state->next_output_byte = dest->next_output_byte; 330 state->free_in_buffer = dest->free_in_buffer; 331 return TRUE; 332} 333 334 335/* Outputting bits to the file */ 336 337/* These macros perform the same task as the emit_bits() function in the 338 * original libjpeg code. In addition to reducing overhead by explicitly 339 * inlining the code, additional performance is achieved by taking into 340 * account the size of the bit buffer and waiting until it is almost full 341 * before emptying it. This mostly benefits 64-bit platforms, since 6 342 * bytes can be stored in a 64-bit bit buffer before it has to be emptied. 343 */ 344 345#define EMIT_BYTE() { \ 346 JOCTET c; \ 347 put_bits -= 8; \ 348 c = (JOCTET)GETJOCTET(put_buffer >> put_bits); \ 349 *buffer++ = c; \ 350 if (c == 0xFF) /* need to stuff a zero byte? */ \ 351 *buffer++ = 0; \ 352 } 353 354#define PUT_BITS(code, size) { \ 355 put_bits += size; \ 356 put_buffer = (put_buffer << size) | code; \ 357} 358 359#define CHECKBUF15() { \ 360 if (put_bits > 15) { \ 361 EMIT_BYTE() \ 362 EMIT_BYTE() \ 363 } \ 364} 365 366#define CHECKBUF31() { \ 367 if (put_bits > 31) { \ 368 EMIT_BYTE() \ 369 EMIT_BYTE() \ 370 EMIT_BYTE() \ 371 EMIT_BYTE() \ 372 } \ 373} 374 375#define CHECKBUF47() { \ 376 if (put_bits > 47) { \ 377 EMIT_BYTE() \ 378 EMIT_BYTE() \ 379 EMIT_BYTE() \ 380 EMIT_BYTE() \ 381 EMIT_BYTE() \ 382 EMIT_BYTE() \ 383 } \ 384} 385 386#if !defined(_WIN32) && !defined(SIZEOF_SIZE_T) 387#error Cannot determine word size 388#endif 389 390#if SIZEOF_SIZE_T==8 || defined(_WIN64) 391 392#define EMIT_BITS(code, size) { \ 393 CHECKBUF47() \ 394 PUT_BITS(code, size) \ 395} 396 397#define EMIT_CODE(code, size) { \ 398 temp2 &= (((JLONG) 1)<<nbits) - 1; \ 399 CHECKBUF31() \ 400 PUT_BITS(code, size) \ 401 PUT_BITS(temp2, nbits) \ 402 } 403 404#else 405 406#define EMIT_BITS(code, size) { \ 407 PUT_BITS(code, size) \ 408 CHECKBUF15() \ 409} 410 411#define EMIT_CODE(code, size) { \ 412 temp2 &= (((JLONG) 1)<<nbits) - 1; \ 413 PUT_BITS(code, size) \ 414 CHECKBUF15() \ 415 PUT_BITS(temp2, nbits) \ 416 CHECKBUF15() \ 417 } 418 419#endif 420 421 422/* Although it is exceedingly rare, it is possible for a Huffman-encoded 423 * coefficient block to be larger than the 128-byte unencoded block. For each 424 * of the 64 coefficients, PUT_BITS is invoked twice, and each invocation can 425 * theoretically store 16 bits (for a maximum of 2048 bits or 256 bytes per 426 * encoded block.) If, for instance, one artificially sets the AC 427 * coefficients to alternating values of 32767 and -32768 (using the JPEG 428 * scanning order-- 1, 8, 16, etc.), then this will produce an encoded block 429 * larger than 200 bytes. 430 */ 431#define BUFSIZE (DCTSIZE2 * 4) 432 433#define LOAD_BUFFER() { \ 434 if (state->free_in_buffer < BUFSIZE) { \ 435 localbuf = 1; \ 436 buffer = _buffer; \ 437 } \ 438 else buffer = state->next_output_byte; \ 439 } 440 441#define STORE_BUFFER() { \ 442 if (localbuf) { \ 443 bytes = buffer - _buffer; \ 444 buffer = _buffer; \ 445 while (bytes > 0) { \ 446 bytestocopy = min(bytes, state->free_in_buffer); \ 447 MEMCOPY(state->next_output_byte, buffer, bytestocopy); \ 448 state->next_output_byte += bytestocopy; \ 449 buffer += bytestocopy; \ 450 state->free_in_buffer -= bytestocopy; \ 451 if (state->free_in_buffer == 0) \ 452 if (! dump_buffer(state)) return FALSE; \ 453 bytes -= bytestocopy; \ 454 } \ 455 } \ 456 else { \ 457 state->free_in_buffer -= (buffer - state->next_output_byte); \ 458 state->next_output_byte = buffer; \ 459 } \ 460 } 461 462 463LOCAL(boolean) 464flush_bits (working_state *state) 465{ 466 JOCTET _buffer[BUFSIZE], *buffer; 467 size_t put_buffer; int put_bits; 468 size_t bytes, bytestocopy; int localbuf = 0; 469 470 put_buffer = state->cur.put_buffer; 471 put_bits = state->cur.put_bits; 472 LOAD_BUFFER() 473 474 /* fill any partial byte with ones */ 475 PUT_BITS(0x7F, 7) 476 while (put_bits >= 8) EMIT_BYTE() 477 478 state->cur.put_buffer = 0; /* and reset bit-buffer to empty */ 479 state->cur.put_bits = 0; 480 STORE_BUFFER() 481 482 return TRUE; 483} 484 485 486/* Encode a single block's worth of coefficients */ 487 488LOCAL(boolean) 489encode_one_block_simd (working_state *state, JCOEFPTR block, int last_dc_val, 490 c_derived_tbl *dctbl, c_derived_tbl *actbl) 491{ 492 JOCTET _buffer[BUFSIZE], *buffer; 493 size_t bytes, bytestocopy; int localbuf = 0; 494 495 LOAD_BUFFER() 496 497 buffer = jsimd_huff_encode_one_block(state, buffer, block, last_dc_val, 498 dctbl, actbl); 499 500 STORE_BUFFER() 501 502 return TRUE; 503} 504 505LOCAL(boolean) 506encode_one_block (working_state *state, JCOEFPTR block, int last_dc_val, 507 c_derived_tbl *dctbl, c_derived_tbl *actbl) 508{ 509 int temp, temp2, temp3; 510 int nbits; 511 int r, code, size; 512 JOCTET _buffer[BUFSIZE], *buffer; 513 size_t put_buffer; int put_bits; 514 int code_0xf0 = actbl->ehufco[0xf0], size_0xf0 = actbl->ehufsi[0xf0]; 515 size_t bytes, bytestocopy; int localbuf = 0; 516 517 put_buffer = state->cur.put_buffer; 518 put_bits = state->cur.put_bits; 519 LOAD_BUFFER() 520 521 /* Encode the DC coefficient difference per section F.1.2.1 */ 522 523 temp = temp2 = block[0] - last_dc_val; 524 525 /* This is a well-known technique for obtaining the absolute value without a 526 * branch. It is derived from an assembly language technique presented in 527 * "How to Optimize for the Pentium Processors", Copyright (c) 1996, 1997 by 528 * Agner Fog. 529 */ 530 temp3 = temp >> (CHAR_BIT * sizeof(int) - 1); 531 temp ^= temp3; 532 temp -= temp3; 533 534 /* For a negative input, want temp2 = bitwise complement of abs(input) */ 535 /* This code assumes we are on a two's complement machine */ 536 temp2 += temp3; 537 538 /* Find the number of bits needed for the magnitude of the coefficient */ 539 nbits = JPEG_NBITS(temp); 540 541 /* Emit the Huffman-coded symbol for the number of bits */ 542 code = dctbl->ehufco[nbits]; 543 size = dctbl->ehufsi[nbits]; 544 EMIT_BITS(code, size) 545 546 /* Mask off any extra bits in code */ 547 temp2 &= (((JLONG) 1)<<nbits) - 1; 548 549 /* Emit that number of bits of the value, if positive, */ 550 /* or the complement of its magnitude, if negative. */ 551 EMIT_BITS(temp2, nbits) 552 553 /* Encode the AC coefficients per section F.1.2.2 */ 554 555 r = 0; /* r = run length of zeros */ 556 557/* Manually unroll the k loop to eliminate the counter variable. This 558 * improves performance greatly on systems with a limited number of 559 * registers (such as x86.) 560 */ 561#define kloop(jpeg_natural_order_of_k) { \ 562 if ((temp = block[jpeg_natural_order_of_k]) == 0) { \ 563 r++; \ 564 } else { \ 565 temp2 = temp; \ 566 /* Branch-less absolute value, bitwise complement, etc., same as above */ \ 567 temp3 = temp >> (CHAR_BIT * sizeof(int) - 1); \ 568 temp ^= temp3; \ 569 temp -= temp3; \ 570 temp2 += temp3; \ 571 nbits = JPEG_NBITS_NONZERO(temp); \ 572 /* if run length > 15, must emit special run-length-16 codes (0xF0) */ \ 573 while (r > 15) { \ 574 EMIT_BITS(code_0xf0, size_0xf0) \ 575 r -= 16; \ 576 } \ 577 /* Emit Huffman symbol for run length / number of bits */ \ 578 temp3 = (r << 4) + nbits; \ 579 code = actbl->ehufco[temp3]; \ 580 size = actbl->ehufsi[temp3]; \ 581 EMIT_CODE(code, size) \ 582 r = 0; \ 583 } \ 584} 585 586 /* One iteration for each value in jpeg_natural_order[] */ 587 kloop(1); kloop(8); kloop(16); kloop(9); kloop(2); kloop(3); 588 kloop(10); kloop(17); kloop(24); kloop(32); kloop(25); kloop(18); 589 kloop(11); kloop(4); kloop(5); kloop(12); kloop(19); kloop(26); 590 kloop(33); kloop(40); kloop(48); kloop(41); kloop(34); kloop(27); 591 kloop(20); kloop(13); kloop(6); kloop(7); kloop(14); kloop(21); 592 kloop(28); kloop(35); kloop(42); kloop(49); kloop(56); kloop(57); 593 kloop(50); kloop(43); kloop(36); kloop(29); kloop(22); kloop(15); 594 kloop(23); kloop(30); kloop(37); kloop(44); kloop(51); kloop(58); 595 kloop(59); kloop(52); kloop(45); kloop(38); kloop(31); kloop(39); 596 kloop(46); kloop(53); kloop(60); kloop(61); kloop(54); kloop(47); 597 kloop(55); kloop(62); kloop(63); 598 599 /* If the last coef(s) were zero, emit an end-of-block code */ 600 if (r > 0) { 601 code = actbl->ehufco[0]; 602 size = actbl->ehufsi[0]; 603 EMIT_BITS(code, size) 604 } 605 606 state->cur.put_buffer = put_buffer; 607 state->cur.put_bits = put_bits; 608 STORE_BUFFER() 609 610 return TRUE; 611} 612 613 614/* 615 * Emit a restart marker & resynchronize predictions. 616 */ 617 618LOCAL(boolean) 619emit_restart (working_state *state, int restart_num) 620{ 621 int ci; 622 623 if (! flush_bits(state)) 624 return FALSE; 625 626 emit_byte(state, 0xFF, return FALSE); 627 emit_byte(state, JPEG_RST0 + restart_num, return FALSE); 628 629 /* Re-initialize DC predictions to 0 */ 630 for (ci = 0; ci < state->cinfo->comps_in_scan; ci++) 631 state->cur.last_dc_val[ci] = 0; 632 633 /* The restart counter is not updated until we successfully write the MCU. */ 634 635 return TRUE; 636} 637 638 639/* 640 * Encode and output one MCU's worth of Huffman-compressed coefficients. 641 */ 642 643METHODDEF(boolean) 644encode_mcu_huff (j_compress_ptr cinfo, JBLOCKROW *MCU_data) 645{ 646 huff_entropy_ptr entropy = (huff_entropy_ptr) cinfo->entropy; 647 working_state state; 648 int blkn, ci; 649 jpeg_component_info *compptr; 650 651 /* Load up working state */ 652 state.next_output_byte = cinfo->dest->next_output_byte; 653 state.free_in_buffer = cinfo->dest->free_in_buffer; 654 ASSIGN_STATE(state.cur, entropy->saved); 655 state.cinfo = cinfo; 656 657 /* Emit restart marker if needed */ 658 if (cinfo->restart_interval) { 659 if (entropy->restarts_to_go == 0) 660 if (! emit_restart(&state, entropy->next_restart_num)) 661 return FALSE; 662 } 663 664 /* Encode the MCU data blocks */ 665 if (entropy->simd) { 666 for (blkn = 0; blkn < cinfo->blocks_in_MCU; blkn++) { 667 ci = cinfo->MCU_membership[blkn]; 668 compptr = cinfo->cur_comp_info[ci]; 669 if (! encode_one_block_simd(&state, 670 MCU_data[blkn][0], state.cur.last_dc_val[ci], 671 entropy->dc_derived_tbls[compptr->dc_tbl_no], 672 entropy->ac_derived_tbls[compptr->ac_tbl_no])) 673 return FALSE; 674 /* Update last_dc_val */ 675 state.cur.last_dc_val[ci] = MCU_data[blkn][0][0]; 676 } 677 } else { 678 for (blkn = 0; blkn < cinfo->blocks_in_MCU; blkn++) { 679 ci = cinfo->MCU_membership[blkn]; 680 compptr = cinfo->cur_comp_info[ci]; 681 if (! encode_one_block(&state, 682 MCU_data[blkn][0], state.cur.last_dc_val[ci], 683 entropy->dc_derived_tbls[compptr->dc_tbl_no], 684 entropy->ac_derived_tbls[compptr->ac_tbl_no])) 685 return FALSE; 686 /* Update last_dc_val */ 687 state.cur.last_dc_val[ci] = MCU_data[blkn][0][0]; 688 } 689 } 690 691 /* Completed MCU, so update state */ 692 cinfo->dest->next_output_byte = state.next_output_byte; 693 cinfo->dest->free_in_buffer = state.free_in_buffer; 694 ASSIGN_STATE(entropy->saved, state.cur); 695 696 /* Update restart-interval state too */ 697 if (cinfo->restart_interval) { 698 if (entropy->restarts_to_go == 0) { 699 entropy->restarts_to_go = cinfo->restart_interval; 700 entropy->next_restart_num++; 701 entropy->next_restart_num &= 7; 702 } 703 entropy->restarts_to_go--; 704 } 705 706 return TRUE; 707} 708 709 710/* 711 * Finish up at the end of a Huffman-compressed scan. 712 */ 713 714METHODDEF(void) 715finish_pass_huff (j_compress_ptr cinfo) 716{ 717 huff_entropy_ptr entropy = (huff_entropy_ptr) cinfo->entropy; 718 working_state state; 719 720 /* Load up working state ... flush_bits needs it */ 721 state.next_output_byte = cinfo->dest->next_output_byte; 722 state.free_in_buffer = cinfo->dest->free_in_buffer; 723 ASSIGN_STATE(state.cur, entropy->saved); 724 state.cinfo = cinfo; 725 726 /* Flush out the last data */ 727 if (! flush_bits(&state)) 728 ERREXIT(cinfo, JERR_CANT_SUSPEND); 729 730 /* Update state */ 731 cinfo->dest->next_output_byte = state.next_output_byte; 732 cinfo->dest->free_in_buffer = state.free_in_buffer; 733 ASSIGN_STATE(entropy->saved, state.cur); 734} 735 736 737/* 738 * Huffman coding optimization. 739 * 740 * We first scan the supplied data and count the number of uses of each symbol 741 * that is to be Huffman-coded. (This process MUST agree with the code above.) 742 * Then we build a Huffman coding tree for the observed counts. 743 * Symbols which are not needed at all for the particular image are not 744 * assigned any code, which saves space in the DHT marker as well as in 745 * the compressed data. 746 */ 747 748#ifdef ENTROPY_OPT_SUPPORTED 749 750 751/* Process a single block's worth of coefficients */ 752 753LOCAL(void) 754htest_one_block (j_compress_ptr cinfo, JCOEFPTR block, int last_dc_val, 755 long dc_counts[], long ac_counts[]) 756{ 757 register int temp; 758 register int nbits; 759 register int k, r; 760 761 /* Encode the DC coefficient difference per section F.1.2.1 */ 762 763 temp = block[0] - last_dc_val; 764 if (temp < 0) 765 temp = -temp; 766 767 /* Find the number of bits needed for the magnitude of the coefficient */ 768 nbits = 0; 769 while (temp) { 770 nbits++; 771 temp >>= 1; 772 } 773 /* Check for out-of-range coefficient values. 774 * Since we're encoding a difference, the range limit is twice as much. 775 */ 776 if (nbits > MAX_COEF_BITS+1) 777 ERREXIT(cinfo, JERR_BAD_DCT_COEF); 778 779 /* Count the Huffman symbol for the number of bits */ 780 dc_counts[nbits]++; 781 782 /* Encode the AC coefficients per section F.1.2.2 */ 783 784 r = 0; /* r = run length of zeros */ 785 786 for (k = 1; k < DCTSIZE2; k++) { 787 if ((temp = block[jpeg_natural_order[k]]) == 0) { 788 r++; 789 } else { 790 /* if run length > 15, must emit special run-length-16 codes (0xF0) */ 791 while (r > 15) { 792 ac_counts[0xF0]++; 793 r -= 16; 794 } 795 796 /* Find the number of bits needed for the magnitude of the coefficient */ 797 if (temp < 0) 798 temp = -temp; 799 800 /* Find the number of bits needed for the magnitude of the coefficient */ 801 nbits = 1; /* there must be at least one 1 bit */ 802 while ((temp >>= 1)) 803 nbits++; 804 /* Check for out-of-range coefficient values */ 805 if (nbits > MAX_COEF_BITS) 806 ERREXIT(cinfo, JERR_BAD_DCT_COEF); 807 808 /* Count Huffman symbol for run length / number of bits */ 809 ac_counts[(r << 4) + nbits]++; 810 811 r = 0; 812 } 813 } 814 815 /* If the last coef(s) were zero, emit an end-of-block code */ 816 if (r > 0) 817 ac_counts[0]++; 818} 819 820 821/* 822 * Trial-encode one MCU's worth of Huffman-compressed coefficients. 823 * No data is actually output, so no suspension return is possible. 824 */ 825 826METHODDEF(boolean) 827encode_mcu_gather (j_compress_ptr cinfo, JBLOCKROW *MCU_data) 828{ 829 huff_entropy_ptr entropy = (huff_entropy_ptr) cinfo->entropy; 830 int blkn, ci; 831 jpeg_component_info *compptr; 832 833 /* Take care of restart intervals if needed */ 834 if (cinfo->restart_interval) { 835 if (entropy->restarts_to_go == 0) { 836 /* Re-initialize DC predictions to 0 */ 837 for (ci = 0; ci < cinfo->comps_in_scan; ci++) 838 entropy->saved.last_dc_val[ci] = 0; 839 /* Update restart state */ 840 entropy->restarts_to_go = cinfo->restart_interval; 841 } 842 entropy->restarts_to_go--; 843 } 844 845 for (blkn = 0; blkn < cinfo->blocks_in_MCU; blkn++) { 846 ci = cinfo->MCU_membership[blkn]; 847 compptr = cinfo->cur_comp_info[ci]; 848 htest_one_block(cinfo, MCU_data[blkn][0], entropy->saved.last_dc_val[ci], 849 entropy->dc_count_ptrs[compptr->dc_tbl_no], 850 entropy->ac_count_ptrs[compptr->ac_tbl_no]); 851 entropy->saved.last_dc_val[ci] = MCU_data[blkn][0][0]; 852 } 853 854 return TRUE; 855} 856 857 858/* 859 * Generate the best Huffman code table for the given counts, fill htbl. 860 * Note this is also used by jcphuff.c. 861 * 862 * The JPEG standard requires that no symbol be assigned a codeword of all 863 * one bits (so that padding bits added at the end of a compressed segment 864 * can't look like a valid code). Because of the canonical ordering of 865 * codewords, this just means that there must be an unused slot in the 866 * longest codeword length category. Section K.2 of the JPEG spec suggests 867 * reserving such a slot by pretending that symbol 256 is a valid symbol 868 * with count 1. In theory that's not optimal; giving it count zero but 869 * including it in the symbol set anyway should give a better Huffman code. 870 * But the theoretically better code actually seems to come out worse in 871 * practice, because it produces more all-ones bytes (which incur stuffed 872 * zero bytes in the final file). In any case the difference is tiny. 873 * 874 * The JPEG standard requires Huffman codes to be no more than 16 bits long. 875 * If some symbols have a very small but nonzero probability, the Huffman tree 876 * must be adjusted to meet the code length restriction. We currently use 877 * the adjustment method suggested in JPEG section K.2. This method is *not* 878 * optimal; it may not choose the best possible limited-length code. But 879 * typically only very-low-frequency symbols will be given less-than-optimal 880 * lengths, so the code is almost optimal. Experimental comparisons against 881 * an optimal limited-length-code algorithm indicate that the difference is 882 * microscopic --- usually less than a hundredth of a percent of total size. 883 * So the extra complexity of an optimal algorithm doesn't seem worthwhile. 884 */ 885 886GLOBAL(void) 887jpeg_gen_optimal_table (j_compress_ptr cinfo, JHUFF_TBL *htbl, long freq[]) 888{ 889#define MAX_CLEN 32 /* assumed maximum initial code length */ 890 UINT8 bits[MAX_CLEN+1]; /* bits[k] = # of symbols with code length k */ 891 int codesize[257]; /* codesize[k] = code length of symbol k */ 892 int others[257]; /* next symbol in current branch of tree */ 893 int c1, c2; 894 int p, i, j; 895 long v; 896 897 /* This algorithm is explained in section K.2 of the JPEG standard */ 898 899 MEMZERO(bits, sizeof(bits)); 900 MEMZERO(codesize, sizeof(codesize)); 901 for (i = 0; i < 257; i++) 902 others[i] = -1; /* init links to empty */ 903 904 freq[256] = 1; /* make sure 256 has a nonzero count */ 905 /* Including the pseudo-symbol 256 in the Huffman procedure guarantees 906 * that no real symbol is given code-value of all ones, because 256 907 * will be placed last in the largest codeword category. 908 */ 909 910 /* Huffman's basic algorithm to assign optimal code lengths to symbols */ 911 912 for (;;) { 913 /* Find the smallest nonzero frequency, set c1 = its symbol */ 914 /* In case of ties, take the larger symbol number */ 915 c1 = -1; 916 v = 1000000000L; 917 for (i = 0; i <= 256; i++) { 918 if (freq[i] && freq[i] <= v) { 919 v = freq[i]; 920 c1 = i; 921 } 922 } 923 924 /* Find the next smallest nonzero frequency, set c2 = its symbol */ 925 /* In case of ties, take the larger symbol number */ 926 c2 = -1; 927 v = 1000000000L; 928 for (i = 0; i <= 256; i++) { 929 if (freq[i] && freq[i] <= v && i != c1) { 930 v = freq[i]; 931 c2 = i; 932 } 933 } 934 935 /* Done if we've merged everything into one frequency */ 936 if (c2 < 0) 937 break; 938 939 /* Else merge the two counts/trees */ 940 freq[c1] += freq[c2]; 941 freq[c2] = 0; 942 943 /* Increment the codesize of everything in c1's tree branch */ 944 codesize[c1]++; 945 while (others[c1] >= 0) { 946 c1 = others[c1]; 947 codesize[c1]++; 948 } 949 950 others[c1] = c2; /* chain c2 onto c1's tree branch */ 951 952 /* Increment the codesize of everything in c2's tree branch */ 953 codesize[c2]++; 954 while (others[c2] >= 0) { 955 c2 = others[c2]; 956 codesize[c2]++; 957 } 958 } 959 960 /* Now count the number of symbols of each code length */ 961 for (i = 0; i <= 256; i++) { 962 if (codesize[i]) { 963 /* The JPEG standard seems to think that this can't happen, */ 964 /* but I'm paranoid... */ 965 if (codesize[i] > MAX_CLEN) 966 ERREXIT(cinfo, JERR_HUFF_CLEN_OVERFLOW); 967 968 bits[codesize[i]]++; 969 } 970 } 971 972 /* JPEG doesn't allow symbols with code lengths over 16 bits, so if the pure 973 * Huffman procedure assigned any such lengths, we must adjust the coding. 974 * Here is what the JPEG spec says about how this next bit works: 975 * Since symbols are paired for the longest Huffman code, the symbols are 976 * removed from this length category two at a time. The prefix for the pair 977 * (which is one bit shorter) is allocated to one of the pair; then, 978 * skipping the BITS entry for that prefix length, a code word from the next 979 * shortest nonzero BITS entry is converted into a prefix for two code words 980 * one bit longer. 981 */ 982 983 for (i = MAX_CLEN; i > 16; i--) { 984 while (bits[i] > 0) { 985 j = i - 2; /* find length of new prefix to be used */ 986 while (bits[j] == 0) 987 j--; 988 989 bits[i] -= 2; /* remove two symbols */ 990 bits[i-1]++; /* one goes in this length */ 991 bits[j+1] += 2; /* two new symbols in this length */ 992 bits[j]--; /* symbol of this length is now a prefix */ 993 } 994 } 995 996 /* Remove the count for the pseudo-symbol 256 from the largest codelength */ 997 while (bits[i] == 0) /* find largest codelength still in use */ 998 i--; 999 bits[i]--; 1000 1001 /* Return final symbol counts (only for lengths 0..16) */ 1002 MEMCOPY(htbl->bits, bits, sizeof(htbl->bits)); 1003 1004 /* Return a list of the symbols sorted by code length */ 1005 /* It's not real clear to me why we don't need to consider the codelength 1006 * changes made above, but the JPEG spec seems to think this works. 1007 */ 1008 p = 0; 1009 for (i = 1; i <= MAX_CLEN; i++) { 1010 for (j = 0; j <= 255; j++) { 1011 if (codesize[j] == i) { 1012 htbl->huffval[p] = (UINT8) j; 1013 p++; 1014 } 1015 } 1016 } 1017 1018 /* Set sent_table FALSE so updated table will be written to JPEG file. */ 1019 htbl->sent_table = FALSE; 1020} 1021 1022 1023/* 1024 * Finish up a statistics-gathering pass and create the new Huffman tables. 1025 */ 1026 1027METHODDEF(void) 1028finish_pass_gather (j_compress_ptr cinfo) 1029{ 1030 huff_entropy_ptr entropy = (huff_entropy_ptr) cinfo->entropy; 1031 int ci, dctbl, actbl; 1032 jpeg_component_info *compptr; 1033 JHUFF_TBL **htblptr; 1034 boolean did_dc[NUM_HUFF_TBLS]; 1035 boolean did_ac[NUM_HUFF_TBLS]; 1036 1037 /* It's important not to apply jpeg_gen_optimal_table more than once 1038 * per table, because it clobbers the input frequency counts! 1039 */ 1040 MEMZERO(did_dc, sizeof(did_dc)); 1041 MEMZERO(did_ac, sizeof(did_ac)); 1042 1043 for (ci = 0; ci < cinfo->comps_in_scan; ci++) { 1044 compptr = cinfo->cur_comp_info[ci]; 1045 dctbl = compptr->dc_tbl_no; 1046 actbl = compptr->ac_tbl_no; 1047 if (! did_dc[dctbl]) { 1048 htblptr = & cinfo->dc_huff_tbl_ptrs[dctbl]; 1049 if (*htblptr == NULL) 1050 *htblptr = jpeg_alloc_huff_table((j_common_ptr) cinfo); 1051 jpeg_gen_optimal_table(cinfo, *htblptr, entropy->dc_count_ptrs[dctbl]); 1052 did_dc[dctbl] = TRUE; 1053 } 1054 if (! did_ac[actbl]) { 1055 htblptr = & cinfo->ac_huff_tbl_ptrs[actbl]; 1056 if (*htblptr == NULL) 1057 *htblptr = jpeg_alloc_huff_table((j_common_ptr) cinfo); 1058 jpeg_gen_optimal_table(cinfo, *htblptr, entropy->ac_count_ptrs[actbl]); 1059 did_ac[actbl] = TRUE; 1060 } 1061 } 1062} 1063 1064 1065#endif /* ENTROPY_OPT_SUPPORTED */ 1066 1067 1068/* 1069 * Module initialization routine for Huffman entropy encoding. 1070 */ 1071 1072GLOBAL(void) 1073jinit_huff_encoder (j_compress_ptr cinfo) 1074{ 1075 huff_entropy_ptr entropy; 1076 int i; 1077 1078 entropy = (huff_entropy_ptr) 1079 (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE, 1080 sizeof(huff_entropy_encoder)); 1081 cinfo->entropy = (struct jpeg_entropy_encoder *) entropy; 1082 entropy->pub.start_pass = start_pass_huff; 1083 1084 /* Mark tables unallocated */ 1085 for (i = 0; i < NUM_HUFF_TBLS; i++) { 1086 entropy->dc_derived_tbls[i] = entropy->ac_derived_tbls[i] = NULL; 1087#ifdef ENTROPY_OPT_SUPPORTED 1088 entropy->dc_count_ptrs[i] = entropy->ac_count_ptrs[i] = NULL; 1089#endif 1090 } 1091} 1092