4 * Copyright (C) 1991-1995, 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.
8 * This file contains Huffman entropy decoding routines.
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.
17 #define JPEG_INTERNALS
19 #include "radiant_jpeglib.h"
20 #include "jdhuff.h" /* Declarations shared with jdphuff.c */
24 * Expanded entropy decoder object for Huffman decoding.
26 * The savable_state subrecord contains fields that change within an MCU,
27 * but must not be updated permanently until we complete the MCU.
31 int last_dc_val[MAX_COMPS_IN_SCAN]; /* last DC coef for each component */
34 /* This macro is to work around compilers with missing or broken
35 * structure assignment. You'll need to fix this code if you have
36 * such a compiler and you change MAX_COMPS_IN_SCAN.
39 #ifndef NO_STRUCT_ASSIGN
40 #define ASSIGN_STATE(dest,src) ((dest) = (src))
42 #if MAX_COMPS_IN_SCAN == 4
43 #define ASSIGN_STATE(dest,src) \
44 ((dest).last_dc_val[0] = (src).last_dc_val[0], \
45 (dest).last_dc_val[1] = (src).last_dc_val[1], \
46 (dest).last_dc_val[2] = (src).last_dc_val[2], \
47 (dest).last_dc_val[3] = (src).last_dc_val[3])
53 struct jpeg_entropy_decoder pub; /* public fields */
55 /* These fields are loaded into local variables at start of each MCU.
56 * In case of suspension, we exit WITHOUT updating them.
58 bitread_perm_state bitstate; /* Bit buffer at start of MCU */
59 savable_state saved; /* Other state at start of MCU */
61 /* These fields are NOT loaded into local working state. */
62 unsigned int restarts_to_go; /* MCUs left in this restart interval */
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 } huff_entropy_decoder;
69 typedef huff_entropy_decoder * huff_entropy_ptr;
73 * Initialize for a Huffman-compressed scan.
77 start_pass_huff_decoder (j_decompress_ptr cinfo)
79 huff_entropy_ptr entropy = (huff_entropy_ptr) cinfo->entropy;
81 jpeg_component_info * compptr;
83 /* Check that the scan parameters Ss, Se, Ah/Al are OK for sequential JPEG.
84 * This ought to be an error condition, but we make it a warning because
85 * there are some baseline files out there with all zeroes in these bytes.
87 if (cinfo->Ss != 0 || cinfo->Se != DCTSIZE2-1 ||
88 cinfo->Ah != 0 || cinfo->Al != 0)
89 WARNMS(cinfo, JWRN_NOT_SEQUENTIAL);
91 for (ci = 0; ci < cinfo->comps_in_scan; ci++) {
92 compptr = cinfo->cur_comp_info[ci];
93 dctbl = compptr->dc_tbl_no;
94 actbl = compptr->ac_tbl_no;
95 /* Make sure requested tables are present */
96 if (dctbl < 0 || dctbl >= NUM_HUFF_TBLS ||
97 cinfo->dc_huff_tbl_ptrs[dctbl] == NULL)
98 ERREXIT1(cinfo, JERR_NO_HUFF_TABLE, dctbl);
99 if (actbl < 0 || actbl >= NUM_HUFF_TBLS ||
100 cinfo->ac_huff_tbl_ptrs[actbl] == NULL)
101 ERREXIT1(cinfo, JERR_NO_HUFF_TABLE, actbl);
102 /* Compute derived values for Huffman tables */
103 /* We may do this more than once for a table, but it's not expensive */
104 jpeg_make_d_derived_tbl(cinfo, cinfo->dc_huff_tbl_ptrs[dctbl],
105 & entropy->dc_derived_tbls[dctbl]);
106 jpeg_make_d_derived_tbl(cinfo, cinfo->ac_huff_tbl_ptrs[actbl],
107 & entropy->ac_derived_tbls[actbl]);
108 /* Initialize DC predictions to 0 */
109 entropy->saved.last_dc_val[ci] = 0;
112 /* Initialize bitread state variables */
113 entropy->bitstate.bits_left = 0;
114 entropy->bitstate.get_buffer = 0; /* unnecessary, but keeps Purify quiet */
115 entropy->bitstate.printed_eod = FALSE;
117 /* Initialize restart counter */
118 entropy->restarts_to_go = cinfo->restart_interval;
123 * Compute the derived values for a Huffman table.
124 * Note this is also used by jdphuff.c.
128 jpeg_make_d_derived_tbl (j_decompress_ptr cinfo, JHUFF_TBL * htbl,
129 d_derived_tbl ** pdtbl)
135 unsigned int huffcode[257];
138 /* Allocate a workspace if we haven't already done so. */
140 *pdtbl = (d_derived_tbl *)
141 (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE,
142 SIZEOF(d_derived_tbl));
144 dtbl->pub = htbl; /* fill in back link */
146 /* Figure C.1: make table of Huffman code length for each symbol */
147 /* Note that this is in code-length order. */
150 for (l = 1; l <= 16; l++) {
151 for (i = 1; i <= (int) htbl->bits[l]; i++)
152 huffsize[p++] = (char) l;
156 /* Figure C.2: generate the codes themselves */
157 /* Note that this is in code-length order. */
162 while (huffsize[p]) {
163 while (((int) huffsize[p]) == si) {
164 huffcode[p++] = code;
171 /* Figure F.15: generate decoding tables for bit-sequential decoding */
174 for (l = 1; l <= 16; l++) {
176 dtbl->valptr[l] = p; /* huffval[] index of 1st symbol of code length l */
177 dtbl->mincode[l] = huffcode[p]; /* minimum code of length l */
179 dtbl->maxcode[l] = huffcode[p-1]; /* maximum code of length l */
181 dtbl->maxcode[l] = -1; /* -1 if no codes of this length */
184 dtbl->maxcode[17] = 0xFFFFFL; /* ensures jpeg_huff_decode terminates */
186 /* Compute lookahead tables to speed up decoding.
187 * First we set all the table entries to 0, indicating "too long";
188 * then we iterate through the Huffman codes that are short enough and
189 * fill in all the entries that correspond to bit sequences starting
193 MEMZERO(dtbl->look_nbits, SIZEOF(dtbl->look_nbits));
196 for (l = 1; l <= HUFF_LOOKAHEAD; l++) {
197 for (i = 1; i <= (int) htbl->bits[l]; i++, p++) {
198 /* l = current code's length, p = its index in huffcode[] & huffval[]. */
199 /* Generate left-justified code followed by all possible bit sequences */
200 lookbits = huffcode[p] << (HUFF_LOOKAHEAD-l);
201 for (ctr = 1 << (HUFF_LOOKAHEAD-l); ctr > 0; ctr--) {
202 dtbl->look_nbits[lookbits] = l;
203 dtbl->look_sym[lookbits] = htbl->huffval[p];
212 * Out-of-line code for bit fetching (shared with jdphuff.c).
213 * See jdhuff.h for info about usage.
214 * Note: current values of get_buffer and bits_left are passed as parameters,
215 * but are returned in the corresponding fields of the state struct.
217 * On most machines MIN_GET_BITS should be 25 to allow the full 32-bit width
218 * of get_buffer to be used. (On machines with wider words, an even larger
219 * buffer could be used.) However, on some machines 32-bit shifts are
220 * quite slow and take time proportional to the number of places shifted.
221 * (This is true with most PC compilers, for instance.) In this case it may
222 * be a win to set MIN_GET_BITS to the minimum value of 15. This reduces the
223 * average shift distance at the cost of more calls to jpeg_fill_bit_buffer.
227 #define MIN_GET_BITS 15 /* minimum allowable value */
229 #define MIN_GET_BITS (BIT_BUF_SIZE-7)
234 jpeg_fill_bit_buffer (bitread_working_state * state,
235 register bit_buf_type get_buffer, register int bits_left,
237 /* Load up the bit buffer to a depth of at least nbits */
239 /* Copy heavily used state fields into locals (hopefully registers) */
240 register const JOCTET * next_input_byte = state->next_input_byte;
241 register size_t bytes_in_buffer = state->bytes_in_buffer;
244 /* Attempt to load at least MIN_GET_BITS bits into get_buffer. */
245 /* (It is assumed that no request will be for more than that many bits.) */
247 while (bits_left < MIN_GET_BITS) {
248 /* Attempt to read a byte */
249 if (state->unread_marker != 0)
250 goto no_more_data; /* can't advance past a marker */
252 if (bytes_in_buffer == 0) {
253 if (! (*state->cinfo->src->fill_input_buffer) (state->cinfo))
255 next_input_byte = state->cinfo->src->next_input_byte;
256 bytes_in_buffer = state->cinfo->src->bytes_in_buffer;
259 c = GETJOCTET(*next_input_byte++);
261 /* If it's 0xFF, check and discard stuffed zero byte */
264 if (bytes_in_buffer == 0) {
265 if (! (*state->cinfo->src->fill_input_buffer) (state->cinfo))
267 next_input_byte = state->cinfo->src->next_input_byte;
268 bytes_in_buffer = state->cinfo->src->bytes_in_buffer;
271 c = GETJOCTET(*next_input_byte++);
275 /* Found FF/00, which represents an FF data byte */
278 /* Oops, it's actually a marker indicating end of compressed data. */
279 /* Better put it back for use later */
280 state->unread_marker = c;
283 /* There should be enough bits still left in the data segment; */
284 /* if so, just break out of the outer while loop. */
285 if (bits_left >= nbits)
287 /* Uh-oh. Report corrupted data to user and stuff zeroes into
288 * the data stream, so that we can produce some kind of image.
289 * Note that this code will be repeated for each byte demanded
290 * for the rest of the segment. We use a nonvolatile flag to ensure
291 * that only one warning message appears.
293 if (! *(state->printed_eod_ptr)) {
294 WARNMS(state->cinfo, JWRN_HIT_MARKER);
295 *(state->printed_eod_ptr) = TRUE;
297 c = 0; /* insert a zero byte into bit buffer */
301 /* OK, load c into get_buffer */
302 get_buffer = (get_buffer << 8) | c;
306 /* Unload the local registers */
307 state->next_input_byte = next_input_byte;
308 state->bytes_in_buffer = bytes_in_buffer;
309 state->get_buffer = get_buffer;
310 state->bits_left = bits_left;
317 * Out-of-line code for Huffman code decoding.
318 * See jdhuff.h for info about usage.
322 jpeg_huff_decode (bitread_working_state * state,
323 register bit_buf_type get_buffer, register int bits_left,
324 d_derived_tbl * htbl, int min_bits)
326 register int l = min_bits;
329 /* HUFF_DECODE has determined that the code is at least min_bits */
330 /* bits long, so fetch that many bits in one swoop. */
332 CHECK_BIT_BUFFER(*state, l, return -1);
335 /* Collect the rest of the Huffman code one bit at a time. */
336 /* This is per Figure F.16 in the JPEG spec. */
338 while (code > htbl->maxcode[l]) {
340 CHECK_BIT_BUFFER(*state, 1, return -1);
345 /* Unload the local registers */
346 state->get_buffer = get_buffer;
347 state->bits_left = bits_left;
349 /* With garbage input we may reach the sentinel value l = 17. */
352 WARNMS(state->cinfo, JWRN_HUFF_BAD_CODE);
353 return 0; /* fake a zero as the safest result */
356 return htbl->pub->huffval[ htbl->valptr[l] +
357 ((int) (code - htbl->mincode[l])) ];
362 * Figure F.12: extend sign bit.
363 * On some machines, a shift and add will be faster than a table lookup.
368 #define HUFF_EXTEND(x,s) ((x) < (1<<((s)-1)) ? (x) + (((-1)<<(s)) + 1) : (x))
372 #define HUFF_EXTEND(x,s) ((x) < extend_test[s] ? (x) + extend_offset[s] : (x))
374 static const int extend_test[16] = /* entry n is 2**(n-1) */
375 { 0, 0x0001, 0x0002, 0x0004, 0x0008, 0x0010, 0x0020, 0x0040, 0x0080,
376 0x0100, 0x0200, 0x0400, 0x0800, 0x1000, 0x2000, 0x4000 };
378 static const int extend_offset[16] = /* entry n is (-1 << n) + 1 */
379 { 0, ((-1)<<1) + 1, ((-1)<<2) + 1, ((-1)<<3) + 1, ((-1)<<4) + 1,
380 ((-1)<<5) + 1, ((-1)<<6) + 1, ((-1)<<7) + 1, ((-1)<<8) + 1,
381 ((-1)<<9) + 1, ((-1)<<10) + 1, ((-1)<<11) + 1, ((-1)<<12) + 1,
382 ((-1)<<13) + 1, ((-1)<<14) + 1, ((-1)<<15) + 1 };
384 #endif /* AVOID_TABLES */
388 * Check for a restart marker & resynchronize decoder.
389 * Returns FALSE if must suspend.
393 process_restart (j_decompress_ptr cinfo)
395 huff_entropy_ptr entropy = (huff_entropy_ptr) cinfo->entropy;
398 /* Throw away any unused bits remaining in bit buffer; */
399 /* include any full bytes in next_marker's count of discarded bytes */
400 cinfo->marker->discarded_bytes += entropy->bitstate.bits_left / 8;
401 entropy->bitstate.bits_left = 0;
403 /* Advance past the RSTn marker */
404 if (! (*cinfo->marker->read_restart_marker) (cinfo))
407 /* Re-initialize DC predictions to 0 */
408 for (ci = 0; ci < cinfo->comps_in_scan; ci++)
409 entropy->saved.last_dc_val[ci] = 0;
411 /* Reset restart counter */
412 entropy->restarts_to_go = cinfo->restart_interval;
414 /* Next segment can get another out-of-data warning */
415 entropy->bitstate.printed_eod = FALSE;
422 * Decode and return one MCU's worth of Huffman-compressed coefficients.
423 * The coefficients are reordered from zigzag order into natural array order,
424 * but are not dequantized.
426 * The i'th block of the MCU is stored into the block pointed to by
427 * MCU_data[i]. WE ASSUME THIS AREA HAS BEEN ZEROED BY THE CALLER.
428 * (Wholesale zeroing is usually a little faster than retail...)
430 * Returns FALSE if data source requested suspension. In that case no
431 * changes have been made to permanent state. (Exception: some output
432 * coefficients may already have been assigned. This is harmless for
433 * this module, since we'll just re-assign them on the next call.)
437 decode_mcu (j_decompress_ptr cinfo, JBLOCKROW *MCU_data)
439 huff_entropy_ptr entropy = (huff_entropy_ptr) cinfo->entropy;
440 register int s, k, r;
445 d_derived_tbl * dctbl;
446 d_derived_tbl * actbl;
447 jpeg_component_info * compptr;
449 /* Process restart marker if needed; may have to suspend */
450 if (cinfo->restart_interval) {
451 if (entropy->restarts_to_go == 0)
452 if (! process_restart(cinfo))
456 /* Load up working state */
457 BITREAD_LOAD_STATE(cinfo,entropy->bitstate);
458 ASSIGN_STATE(state, entropy->saved);
460 /* Outer loop handles each block in the MCU */
462 for (blkn = 0; blkn < cinfo->blocks_in_MCU; blkn++) {
463 block = MCU_data[blkn];
464 ci = cinfo->MCU_membership[blkn];
465 compptr = cinfo->cur_comp_info[ci];
466 dctbl = entropy->dc_derived_tbls[compptr->dc_tbl_no];
467 actbl = entropy->ac_derived_tbls[compptr->ac_tbl_no];
469 /* Decode a single block's worth of coefficients */
471 /* Section F.2.2.1: decode the DC coefficient difference */
472 HUFF_DECODE(s, br_state, dctbl, return FALSE, label1);
474 CHECK_BIT_BUFFER(br_state, s, return FALSE);
476 s = HUFF_EXTEND(r, s);
479 /* Shortcut if component's values are not interesting */
480 if (! compptr->component_needed)
483 /* Convert DC difference to actual value, update last_dc_val */
484 s += state.last_dc_val[ci];
485 state.last_dc_val[ci] = s;
486 /* Output the DC coefficient (assumes jpeg_natural_order[0] = 0) */
487 (*block)[0] = (JCOEF) s;
489 /* Do we need to decode the AC coefficients for this component? */
490 if (compptr->DCT_scaled_size > 1) {
492 /* Section F.2.2.2: decode the AC coefficients */
493 /* Since zeroes are skipped, output area must be cleared beforehand */
494 for (k = 1; k < DCTSIZE2; k++) {
495 HUFF_DECODE(s, br_state, actbl, return FALSE, label2);
502 CHECK_BIT_BUFFER(br_state, s, return FALSE);
504 s = HUFF_EXTEND(r, s);
505 /* Output coefficient in natural (dezigzagged) order.
506 * Note: the extra entries in jpeg_natural_order[] will save us
507 * if k >= DCTSIZE2, which could happen if the data is corrupted.
509 (*block)[jpeg_natural_order[k]] = (JCOEF) s;
520 /* Section F.2.2.2: decode the AC coefficients */
521 /* In this path we just discard the values */
522 for (k = 1; k < DCTSIZE2; k++) {
523 HUFF_DECODE(s, br_state, actbl, return FALSE, label3);
530 CHECK_BIT_BUFFER(br_state, s, return FALSE);
542 /* Completed MCU, so update state */
543 BITREAD_SAVE_STATE(cinfo,entropy->bitstate);
544 ASSIGN_STATE(entropy->saved, state);
546 /* Account for restart interval (no-op if not using restarts) */
547 entropy->restarts_to_go--;
554 * Module initialization routine for Huffman entropy decoding.
558 jinit_huff_decoder (j_decompress_ptr cinfo)
560 huff_entropy_ptr entropy;
563 entropy = (huff_entropy_ptr)
564 (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE,
565 SIZEOF(huff_entropy_decoder));
566 cinfo->entropy = (struct jpeg_entropy_decoder *) entropy;
567 entropy->pub.start_pass = start_pass_huff_decoder;
568 entropy->pub.decode_mcu = decode_mcu;
570 /* Mark tables unallocated */
571 for (i = 0; i < NUM_HUFF_TBLS; i++) {
572 entropy->dc_derived_tbls[i] = entropy->ac_derived_tbls[i] = NULL;