/libjpeg/jdshuff.c
C | 360 lines | 187 code | 68 blank | 105 comment | 37 complexity | 07f339203d76733142849355af822d5e MD5 | raw file
1/* 2 * jdshuff.c 3 * 4 * Copyright (C) 1991-1998, Thomas G. Lane. 5 * This file is part of the Independent JPEG Group's software. 6 * For conditions of distribution and use, see the accompanying README file. 7 * 8 * This file contains Huffman entropy decoding routines for sequential JPEG. 9 * 10 * Much of the complexity here has to do with supporting input suspension. 11 * If the data source module demands suspension, we want to be able to back 12 * up to the start of the current MCU. To do this, we copy state variables 13 * into local working storage, and update them back to the permanent 14 * storage only upon successful completion of an MCU. 15 */ 16 17#define JPEG_INTERNALS 18#include "jinclude.h" 19#include "jpeglib.h" 20#include "jlossy.h" /* Private declarations for lossy codec */ 21#include "jdhuff.h" /* Declarations shared with jd*huff.c */ 22 23 24/* 25 * Private entropy decoder object for Huffman decoding. 26 * 27 * The savable_state subrecord contains fields that change within an MCU, 28 * but must not be updated permanently until we complete the MCU. 29 */ 30 31typedef struct { 32 int last_dc_val[MAX_COMPS_IN_SCAN]; /* last DC coef for each component */ 33} savable_state; 34 35/* This macro is to work around compilers with missing or broken 36 * structure assignment. You'll need to fix this code if you have 37 * such a compiler and you change MAX_COMPS_IN_SCAN. 38 */ 39 40#ifndef NO_STRUCT_ASSIGN 41#define ASSIGN_STATE(dest,src) ((dest) = (src)) 42#else 43#if MAX_COMPS_IN_SCAN == 4 44#define ASSIGN_STATE(dest,src) \ 45 ((dest).last_dc_val[0] = (src).last_dc_val[0], \ 46 (dest).last_dc_val[1] = (src).last_dc_val[1], \ 47 (dest).last_dc_val[2] = (src).last_dc_val[2], \ 48 (dest).last_dc_val[3] = (src).last_dc_val[3]) 49#endif 50#endif 51 52 53typedef struct { 54 huffd_common_fields; /* Fields shared with other entropy decoders */ 55 56 /* These fields are loaded into local variables at start of each MCU. 57 * In case of suspension, we exit WITHOUT updating them. 58 */ 59 savable_state saved; /* Other state at start of MCU */ 60 61 /* These fields are NOT loaded into local working state. */ 62 unsigned int restarts_to_go; /* MCUs left in this restart interval */ 63 64 /* Pointers to derived tables (these workspaces have image lifespan) */ 65 d_derived_tbl * dc_derived_tbls[NUM_HUFF_TBLS]; 66 d_derived_tbl * ac_derived_tbls[NUM_HUFF_TBLS]; 67 68 /* Precalculated info set up by start_pass for use in decode_mcu: */ 69 70 /* Pointers to derived tables to be used for each block within an MCU */ 71 d_derived_tbl * dc_cur_tbls[D_MAX_DATA_UNITS_IN_MCU]; 72 d_derived_tbl * ac_cur_tbls[D_MAX_DATA_UNITS_IN_MCU]; 73 /* Whether we care about the DC and AC coefficient values for each block */ 74 boolean dc_needed[D_MAX_DATA_UNITS_IN_MCU]; 75 boolean ac_needed[D_MAX_DATA_UNITS_IN_MCU]; 76} shuff_entropy_decoder; 77 78typedef shuff_entropy_decoder * shuff_entropy_ptr; 79 80 81/* 82 * Initialize for a Huffman-compressed scan. 83 */ 84 85METHODDEF(void) 86start_pass_huff_decoder (j_decompress_ptr cinfo) 87{ 88 j_lossy_d_ptr lossyd = (j_lossy_d_ptr) cinfo->codec; 89 shuff_entropy_ptr entropy = (shuff_entropy_ptr) lossyd->entropy_private; 90 int ci, blkn, dctbl, actbl; 91 jpeg_component_info * compptr; 92 93 /* Check that the scan parameters Ss, Se, Ah/Al are OK for sequential JPEG. 94 * This ought to be an error condition, but we make it a warning because 95 * there are some baseline files out there with all zeroes in these bytes. 96 */ 97 if (cinfo->Ss != 0 || cinfo->Se != DCTSIZE2-1 || 98 cinfo->Ah != 0 || cinfo->Al != 0) 99 WARNMS(cinfo, JWRN_NOT_SEQUENTIAL); 100 101 for (ci = 0; ci < cinfo->comps_in_scan; ci++) { 102 compptr = cinfo->cur_comp_info[ci]; 103 dctbl = compptr->dc_tbl_no; 104 actbl = compptr->ac_tbl_no; 105 /* Compute derived values for Huffman tables */ 106 /* We may do this more than once for a table, but it's not expensive */ 107 jpeg_make_d_derived_tbl(cinfo, TRUE, dctbl, 108 & entropy->dc_derived_tbls[dctbl]); 109 jpeg_make_d_derived_tbl(cinfo, FALSE, actbl, 110 & entropy->ac_derived_tbls[actbl]); 111 /* Initialize DC predictions to 0 */ 112 entropy->saved.last_dc_val[ci] = 0; 113 } 114 115 /* Precalculate decoding info for each block in an MCU of this scan */ 116 for (blkn = 0; blkn < cinfo->data_units_in_MCU; blkn++) { 117 ci = cinfo->MCU_membership[blkn]; 118 compptr = cinfo->cur_comp_info[ci]; 119 /* Precalculate which table to use for each block */ 120 entropy->dc_cur_tbls[blkn] = entropy->dc_derived_tbls[compptr->dc_tbl_no]; 121 entropy->ac_cur_tbls[blkn] = entropy->ac_derived_tbls[compptr->ac_tbl_no]; 122 /* Decide whether we really care about the coefficient values */ 123 if (compptr->component_needed) { 124 entropy->dc_needed[blkn] = TRUE; 125 /* we don't need the ACs if producing a 1/8th-size image */ 126 entropy->ac_needed[blkn] = (compptr->codec_data_unit > 1); 127 } else { 128 entropy->dc_needed[blkn] = entropy->ac_needed[blkn] = FALSE; 129 } 130 } 131 132 /* Initialize bitread state variables */ 133 entropy->bitstate.bits_left = 0; 134 entropy->bitstate.get_buffer = 0; /* unnecessary, but keeps Purify quiet */ 135 entropy->insufficient_data = FALSE; 136 137 /* Initialize restart counter */ 138 entropy->restarts_to_go = cinfo->restart_interval; 139} 140 141 142/* 143 * Figure F.12: extend sign bit. 144 * On some machines, a shift and add will be faster than a table lookup. 145 */ 146 147#ifdef AVOID_TABLES 148 149#define HUFF_EXTEND(x,s) ((x) < (1<<((s)-1)) ? (x) + (((-1)<<(s)) + 1) : (x)) 150 151#else 152 153#define HUFF_EXTEND(x,s) ((x) < extend_test[s] ? (x) + extend_offset[s] : (x)) 154 155static const int extend_test[16] = /* entry n is 2**(n-1) */ 156 { 0, 0x0001, 0x0002, 0x0004, 0x0008, 0x0010, 0x0020, 0x0040, 0x0080, 157 0x0100, 0x0200, 0x0400, 0x0800, 0x1000, 0x2000, 0x4000 }; 158 159static const int extend_offset[16] = /* entry n is (-1 << n) + 1 */ 160 { 0, ((-1)<<1) + 1, ((-1)<<2) + 1, ((-1)<<3) + 1, ((-1)<<4) + 1, 161 ((-1)<<5) + 1, ((-1)<<6) + 1, ((-1)<<7) + 1, ((-1)<<8) + 1, 162 ((-1)<<9) + 1, ((-1)<<10) + 1, ((-1)<<11) + 1, ((-1)<<12) + 1, 163 ((-1)<<13) + 1, ((-1)<<14) + 1, ((-1)<<15) + 1 }; 164 165#endif /* AVOID_TABLES */ 166 167 168/* 169 * Check for a restart marker & resynchronize decoder. 170 * Returns FALSE if must suspend. 171 */ 172 173LOCAL(boolean) 174process_restart (j_decompress_ptr cinfo) 175{ 176 j_lossy_d_ptr lossyd = (j_lossy_d_ptr) cinfo->codec; 177 shuff_entropy_ptr entropy = (shuff_entropy_ptr) lossyd->entropy_private; 178 int ci; 179 180 /* Throw away any unused bits remaining in bit buffer; */ 181 /* include any full bytes in next_marker's count of discarded bytes */ 182 cinfo->marker->discarded_bytes += entropy->bitstate.bits_left / 8; 183 entropy->bitstate.bits_left = 0; 184 185 /* Advance past the RSTn marker */ 186 if (! (*cinfo->marker->read_restart_marker) (cinfo)) 187 return FALSE; 188 189 /* Re-initialize DC predictions to 0 */ 190 for (ci = 0; ci < cinfo->comps_in_scan; ci++) 191 entropy->saved.last_dc_val[ci] = 0; 192 193 /* Reset restart counter */ 194 entropy->restarts_to_go = cinfo->restart_interval; 195 196 /* Reset out-of-data flag, unless read_restart_marker left us smack up 197 * against a marker. In that case we will end up treating the next data 198 * segment as empty, and we can avoid producing bogus output pixels by 199 * leaving the flag set. 200 */ 201 if (cinfo->unread_marker == 0) 202 entropy->insufficient_data = FALSE; 203 204 return TRUE; 205} 206 207 208/* 209 * Decode and return one MCU's worth of Huffman-compressed coefficients. 210 * The coefficients are reordered from zigzag order into natural array order, 211 * but are not dequantized. 212 * 213 * The i'th block of the MCU is stored into the block pointed to by 214 * MCU_data[i]. WE ASSUME THIS AREA HAS BEEN ZEROED BY THE CALLER. 215 * (Wholesale zeroing is usually a little faster than retail...) 216 * 217 * Returns FALSE if data source requested suspension. In that case no 218 * changes have been made to permanent state. (Exception: some output 219 * coefficients may already have been assigned. This is harmless for 220 * this module, since we'll just re-assign them on the next call.) 221 */ 222 223METHODDEF(boolean) 224decode_mcu (j_decompress_ptr cinfo, JBLOCKROW *MCU_data) 225{ 226 j_lossy_d_ptr lossyd = (j_lossy_d_ptr) cinfo->codec; 227 shuff_entropy_ptr entropy = (shuff_entropy_ptr) lossyd->entropy_private; 228 int blkn; 229 BITREAD_STATE_VARS; 230 savable_state state; 231 232 /* Process restart marker if needed; may have to suspend */ 233 if (cinfo->restart_interval) { 234 if (entropy->restarts_to_go == 0) 235 if (! process_restart(cinfo)) 236 return FALSE; 237 } 238 239 /* If we've run out of data, just leave the MCU set to zeroes. 240 * This way, we return uniform gray for the remainder of the segment. 241 */ 242 if (! entropy->insufficient_data) { 243 244 /* Load up working state */ 245 BITREAD_LOAD_STATE(cinfo,entropy->bitstate); 246 ASSIGN_STATE(state, entropy->saved); 247 248 /* Outer loop handles each block in the MCU */ 249 250 for (blkn = 0; blkn < cinfo->data_units_in_MCU; blkn++) { 251 JBLOCKROW block = MCU_data[blkn]; 252 d_derived_tbl * dctbl = entropy->dc_cur_tbls[blkn]; 253 d_derived_tbl * actbl = entropy->ac_cur_tbls[blkn]; 254 register int s, k, r; 255 256 /* Decode a single block's worth of coefficients */ 257 258 /* Section F.2.2.1: decode the DC coefficient difference */ 259 HUFF_DECODE(s, br_state, dctbl, return FALSE, label1); 260 if (s) { 261 CHECK_BIT_BUFFER(br_state, s, return FALSE); 262 r = GET_BITS(s); 263 s = HUFF_EXTEND(r, s); 264 } 265 266 if (entropy->dc_needed[blkn]) { 267 /* Convert DC difference to actual value, update last_dc_val */ 268 int ci = cinfo->MCU_membership[blkn]; 269 s += state.last_dc_val[ci]; 270 state.last_dc_val[ci] = s; 271 /* Output the DC coefficient (assumes jpeg_natural_order[0] = 0) */ 272 (*block)[0] = (JCOEF) s; 273 } 274 275 if (entropy->ac_needed[blkn]) { 276 277 /* Section F.2.2.2: decode the AC coefficients */ 278 /* Since zeroes are skipped, output area must be cleared beforehand */ 279 for (k = 1; k < DCTSIZE2; k++) { 280 HUFF_DECODE(s, br_state, actbl, return FALSE, label2); 281 282 r = s >> 4; 283 s &= 15; 284 285 if (s) { 286 k += r; 287 CHECK_BIT_BUFFER(br_state, s, return FALSE); 288 r = GET_BITS(s); 289 s = HUFF_EXTEND(r, s); 290 /* Output coefficient in natural (dezigzagged) order. 291 * Note: the extra entries in jpeg_natural_order[] will save us 292 * if k >= DCTSIZE2, which could happen if the data is corrupted. 293 */ 294 (*block)[jpeg_natural_order[k]] = (JCOEF) s; 295 } else { 296 if (r != 15) 297 break; 298 k += 15; 299 } 300 } 301 302 } else { 303 304 /* Section F.2.2.2: decode the AC coefficients */ 305 /* In this path we just discard the values */ 306 for (k = 1; k < DCTSIZE2; k++) { 307 HUFF_DECODE(s, br_state, actbl, return FALSE, label3); 308 309 r = s >> 4; 310 s &= 15; 311 312 if (s) { 313 k += r; 314 CHECK_BIT_BUFFER(br_state, s, return FALSE); 315 DROP_BITS(s); 316 } else { 317 if (r != 15) 318 break; 319 k += 15; 320 } 321 } 322 323 } 324 } 325 326 /* Completed MCU, so update state */ 327 BITREAD_SAVE_STATE(cinfo,entropy->bitstate); 328 ASSIGN_STATE(entropy->saved, state); 329 } 330 331 /* Account for restart interval (no-op if not using restarts) */ 332 entropy->restarts_to_go--; 333 334 return TRUE; 335} 336 337 338/* 339 * Module initialization routine for Huffman entropy decoding. 340 */ 341 342GLOBAL(void) 343jinit_shuff_decoder (j_decompress_ptr cinfo) 344{ 345 j_lossy_d_ptr lossyd = (j_lossy_d_ptr) cinfo->codec; 346 shuff_entropy_ptr entropy; 347 int i; 348 349 entropy = (shuff_entropy_ptr) 350 (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE, 351 SIZEOF(shuff_entropy_decoder)); 352 lossyd->entropy_private = (void *) entropy; 353 lossyd->entropy_start_pass = start_pass_huff_decoder; 354 lossyd->entropy_decode_mcu = decode_mcu; 355 356 /* Mark tables unallocated */ 357 for (i = 0; i < NUM_HUFF_TBLS; i++) { 358 entropy->dc_derived_tbls[i] = entropy->ac_derived_tbls[i] = NULL; 359 } 360}