4 * Copyright (C) 1991-1997, Thomas G. Lane.
5 * Copyright (C) 2009-2011, D. R. Commander.
6 * This file is part of the Independent JPEG Group's software.
7 * For conditions of distribution and use, see the accompanying README file.
9 * This file contains Huffman entropy decoding routines.
11 * Much of the complexity here has to do with supporting input suspension.
12 * If the data source module demands suspension, we want to be able to back
13 * up to the start of the current MCU. To do this, we copy state variables
14 * into local working storage, and update them back to the permanent
15 * storage only upon successful completion of an MCU.
18 #define JPEG_INTERNALS
21 #include "jdhuff.h" /* Declarations shared with jdphuff.c */
26 * Expanded entropy decoder object for Huffman decoding.
28 * The savable_state subrecord contains fields that change within an MCU,
29 * but must not be updated permanently until we complete the MCU.
33 int last_dc_val[MAX_COMPS_IN_SCAN]; /* last DC coef for each component */
36 /* This macro is to work around compilers with missing or broken
37 * structure assignment. You'll need to fix this code if you have
38 * such a compiler and you change MAX_COMPS_IN_SCAN.
41 #ifndef NO_STRUCT_ASSIGN
42 #define ASSIGN_STATE(dest,src) ((dest) = (src))
44 #if MAX_COMPS_IN_SCAN == 4
45 #define ASSIGN_STATE(dest,src) \
46 ((dest).last_dc_val[0] = (src).last_dc_val[0], \
47 (dest).last_dc_val[1] = (src).last_dc_val[1], \
48 (dest).last_dc_val[2] = (src).last_dc_val[2], \
49 (dest).last_dc_val[3] = (src).last_dc_val[3])
55 struct jpeg_entropy_decoder pub; /* public fields */
57 /* These fields are loaded into local variables at start of each MCU.
58 * In case of suspension, we exit WITHOUT updating them.
60 bitread_perm_state bitstate; /* Bit buffer at start of MCU */
61 savable_state saved; /* Other state at start of MCU */
63 /* These fields are NOT loaded into local working state. */
64 unsigned int restarts_to_go; /* MCUs left in this restart interval */
66 /* Pointers to derived tables (these workspaces have image lifespan) */
67 d_derived_tbl * dc_derived_tbls[NUM_HUFF_TBLS];
68 d_derived_tbl * ac_derived_tbls[NUM_HUFF_TBLS];
70 /* Precalculated info set up by start_pass for use in decode_mcu: */
72 /* Pointers to derived tables to be used for each block within an MCU */
73 d_derived_tbl * dc_cur_tbls[D_MAX_BLOCKS_IN_MCU];
74 d_derived_tbl * ac_cur_tbls[D_MAX_BLOCKS_IN_MCU];
75 /* Whether we care about the DC and AC coefficient values for each block */
76 boolean dc_needed[D_MAX_BLOCKS_IN_MCU];
77 boolean ac_needed[D_MAX_BLOCKS_IN_MCU];
78 } huff_entropy_decoder;
80 typedef huff_entropy_decoder * huff_entropy_ptr;
84 * Initialize for a Huffman-compressed scan.
88 start_pass_huff_decoder (j_decompress_ptr cinfo)
90 huff_entropy_ptr entropy = (huff_entropy_ptr) cinfo->entropy;
91 int ci, blkn, dctbl, actbl;
92 jpeg_component_info * compptr;
94 /* Check that the scan parameters Ss, Se, Ah/Al are OK for sequential JPEG.
95 * This ought to be an error condition, but we make it a warning because
96 * there are some baseline files out there with all zeroes in these bytes.
98 if (cinfo->Ss != 0 || cinfo->Se != DCTSIZE2-1 ||
99 cinfo->Ah != 0 || cinfo->Al != 0)
100 WARNMS(cinfo, JWRN_NOT_SEQUENTIAL);
102 for (ci = 0; ci < cinfo->comps_in_scan; ci++) {
103 compptr = cinfo->cur_comp_info[ci];
104 dctbl = compptr->dc_tbl_no;
105 actbl = compptr->ac_tbl_no;
106 /* Compute derived values for Huffman tables */
107 /* We may do this more than once for a table, but it's not expensive */
108 jpeg_make_d_derived_tbl(cinfo, TRUE, dctbl,
109 & entropy->dc_derived_tbls[dctbl]);
110 jpeg_make_d_derived_tbl(cinfo, FALSE, actbl,
111 & entropy->ac_derived_tbls[actbl]);
112 /* Initialize DC predictions to 0 */
113 entropy->saved.last_dc_val[ci] = 0;
116 /* Precalculate decoding info for each block in an MCU of this scan */
117 for (blkn = 0; blkn < cinfo->blocks_in_MCU; blkn++) {
118 ci = cinfo->MCU_membership[blkn];
119 compptr = cinfo->cur_comp_info[ci];
120 /* Precalculate which table to use for each block */
121 entropy->dc_cur_tbls[blkn] = entropy->dc_derived_tbls[compptr->dc_tbl_no];
122 entropy->ac_cur_tbls[blkn] = entropy->ac_derived_tbls[compptr->ac_tbl_no];
123 /* Decide whether we really care about the coefficient values */
124 if (compptr->component_needed) {
125 entropy->dc_needed[blkn] = TRUE;
126 /* we don't need the ACs if producing a 1/8th-size image */
127 entropy->ac_needed[blkn] = (compptr->_DCT_scaled_size > 1);
129 entropy->dc_needed[blkn] = entropy->ac_needed[blkn] = FALSE;
133 /* Initialize bitread state variables */
134 entropy->bitstate.bits_left = 0;
135 entropy->bitstate.get_buffer = 0; /* unnecessary, but keeps Purify quiet */
136 entropy->pub.insufficient_data = FALSE;
138 /* Initialize restart counter */
139 entropy->restarts_to_go = cinfo->restart_interval;
144 * Compute the derived values for a Huffman table.
145 * This routine also performs some validation checks on the table.
147 * Note this is also used by jdphuff.c.
151 jpeg_make_d_derived_tbl (j_decompress_ptr cinfo, boolean isDC, int tblno,
152 d_derived_tbl ** pdtbl)
156 int p, i, l, si, numsymbols;
159 unsigned int huffcode[257];
162 /* Note that huffsize[] and huffcode[] are filled in code-length order,
163 * paralleling the order of the symbols themselves in htbl->huffval[].
166 /* Find the input Huffman table */
167 if (tblno < 0 || tblno >= NUM_HUFF_TBLS)
168 ERREXIT1(cinfo, JERR_NO_HUFF_TABLE, tblno);
170 isDC ? cinfo->dc_huff_tbl_ptrs[tblno] : cinfo->ac_huff_tbl_ptrs[tblno];
172 ERREXIT1(cinfo, JERR_NO_HUFF_TABLE, tblno);
174 /* Allocate a workspace if we haven't already done so. */
176 *pdtbl = (d_derived_tbl *)
177 (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE,
178 SIZEOF(d_derived_tbl));
180 dtbl->pub = htbl; /* fill in back link */
182 /* Figure C.1: make table of Huffman code length for each symbol */
185 for (l = 1; l <= 16; l++) {
186 i = (int) htbl->bits[l];
187 if (i < 0 || p + i > 256) /* protect against table overrun */
188 ERREXIT(cinfo, JERR_BAD_HUFF_TABLE);
190 huffsize[p++] = (char) l;
195 /* Figure C.2: generate the codes themselves */
196 /* We also validate that the counts represent a legal Huffman code tree. */
201 while (huffsize[p]) {
202 while (((int) huffsize[p]) == si) {
203 huffcode[p++] = code;
206 /* code is now 1 more than the last code used for codelength si; but
207 * it must still fit in si bits, since no code is allowed to be all ones.
209 if (((INT32) code) >= (((INT32) 1) << si))
210 ERREXIT(cinfo, JERR_BAD_HUFF_TABLE);
215 /* Figure F.15: generate decoding tables for bit-sequential decoding */
218 for (l = 1; l <= 16; l++) {
220 /* valoffset[l] = huffval[] index of 1st symbol of code length l,
221 * minus the minimum code of length l
223 dtbl->valoffset[l] = (INT32) p - (INT32) huffcode[p];
225 dtbl->maxcode[l] = huffcode[p-1]; /* maximum code of length l */
227 dtbl->maxcode[l] = -1; /* -1 if no codes of this length */
230 dtbl->valoffset[17] = 0;
231 dtbl->maxcode[17] = 0xFFFFFL; /* ensures jpeg_huff_decode terminates */
233 /* Compute lookahead tables to speed up decoding.
234 * First we set all the table entries to 0, indicating "too long";
235 * then we iterate through the Huffman codes that are short enough and
236 * fill in all the entries that correspond to bit sequences starting
240 for (i = 0; i < (1 << HUFF_LOOKAHEAD); i++)
241 dtbl->lookup[i] = (HUFF_LOOKAHEAD + 1) << HUFF_LOOKAHEAD;
244 for (l = 1; l <= HUFF_LOOKAHEAD; l++) {
245 for (i = 1; i <= (int) htbl->bits[l]; i++, p++) {
246 /* l = current code's length, p = its index in huffcode[] & huffval[]. */
247 /* Generate left-justified code followed by all possible bit sequences */
248 lookbits = huffcode[p] << (HUFF_LOOKAHEAD-l);
249 for (ctr = 1 << (HUFF_LOOKAHEAD-l); ctr > 0; ctr--) {
250 dtbl->lookup[lookbits] = (l << HUFF_LOOKAHEAD) | htbl->huffval[p];
256 /* Validate symbols as being reasonable.
257 * For AC tables, we make no check, but accept all byte values 0..255.
258 * For DC tables, we require the symbols to be in range 0..15.
259 * (Tighter bounds could be applied depending on the data depth and mode,
260 * but this is sufficient to ensure safe decoding.)
263 for (i = 0; i < numsymbols; i++) {
264 int sym = htbl->huffval[i];
265 if (sym < 0 || sym > 15)
266 ERREXIT(cinfo, JERR_BAD_HUFF_TABLE);
273 * Out-of-line code for bit fetching (shared with jdphuff.c).
274 * See jdhuff.h for info about usage.
275 * Note: current values of get_buffer and bits_left are passed as parameters,
276 * but are returned in the corresponding fields of the state struct.
278 * On most machines MIN_GET_BITS should be 25 to allow the full 32-bit width
279 * of get_buffer to be used. (On machines with wider words, an even larger
280 * buffer could be used.) However, on some machines 32-bit shifts are
281 * quite slow and take time proportional to the number of places shifted.
282 * (This is true with most PC compilers, for instance.) In this case it may
283 * be a win to set MIN_GET_BITS to the minimum value of 15. This reduces the
284 * average shift distance at the cost of more calls to jpeg_fill_bit_buffer.
288 #define MIN_GET_BITS 15 /* minimum allowable value */
290 #define MIN_GET_BITS (BIT_BUF_SIZE-7)
295 jpeg_fill_bit_buffer (bitread_working_state * state,
296 register bit_buf_type get_buffer, register int bits_left,
298 /* Load up the bit buffer to a depth of at least nbits */
300 /* Copy heavily used state fields into locals (hopefully registers) */
301 register const JOCTET * next_input_byte = state->next_input_byte;
302 register size_t bytes_in_buffer = state->bytes_in_buffer;
303 j_decompress_ptr cinfo = state->cinfo;
305 /* Attempt to load at least MIN_GET_BITS bits into get_buffer. */
306 /* (It is assumed that no request will be for more than that many bits.) */
307 /* We fail to do so only if we hit a marker or are forced to suspend. */
309 if (cinfo->unread_marker == 0) { /* cannot advance past a marker */
310 while (bits_left < MIN_GET_BITS) {
313 /* Attempt to read a byte */
314 if (bytes_in_buffer == 0) {
315 if (! (*cinfo->src->fill_input_buffer) (cinfo))
317 next_input_byte = cinfo->src->next_input_byte;
318 bytes_in_buffer = cinfo->src->bytes_in_buffer;
321 c = GETJOCTET(*next_input_byte++);
323 /* If it's 0xFF, check and discard stuffed zero byte */
325 /* Loop here to discard any padding FF's on terminating marker,
326 * so that we can save a valid unread_marker value. NOTE: we will
327 * accept multiple FF's followed by a 0 as meaning a single FF data
328 * byte. This data pattern is not valid according to the standard.
331 if (bytes_in_buffer == 0) {
332 if (! (*cinfo->src->fill_input_buffer) (cinfo))
334 next_input_byte = cinfo->src->next_input_byte;
335 bytes_in_buffer = cinfo->src->bytes_in_buffer;
338 c = GETJOCTET(*next_input_byte++);
342 /* Found FF/00, which represents an FF data byte */
345 /* Oops, it's actually a marker indicating end of compressed data.
346 * Save the marker code for later use.
347 * Fine point: it might appear that we should save the marker into
348 * bitread working state, not straight into permanent state. But
349 * once we have hit a marker, we cannot need to suspend within the
350 * current MCU, because we will read no more bytes from the data
351 * source. So it is OK to update permanent state right away.
353 cinfo->unread_marker = c;
354 /* See if we need to insert some fake zero bits. */
359 /* OK, load c into get_buffer */
360 get_buffer = (get_buffer << 8) | c;
365 /* We get here if we've read the marker that terminates the compressed
366 * data segment. There should be enough bits in the buffer register
367 * to satisfy the request; if so, no problem.
369 if (nbits > bits_left) {
370 /* Uh-oh. Report corrupted data to user and stuff zeroes into
371 * the data stream, so that we can produce some kind of image.
372 * We use a nonvolatile flag to ensure that only one warning message
373 * appears per data segment.
375 if (! cinfo->entropy->insufficient_data) {
376 WARNMS(cinfo, JWRN_HIT_MARKER);
377 cinfo->entropy->insufficient_data = TRUE;
379 /* Fill the buffer with zero bits */
380 get_buffer <<= MIN_GET_BITS - bits_left;
381 bits_left = MIN_GET_BITS;
385 /* Unload the local registers */
386 state->next_input_byte = next_input_byte;
387 state->bytes_in_buffer = bytes_in_buffer;
388 state->get_buffer = get_buffer;
389 state->bits_left = bits_left;
395 /* Macro version of the above, which performs much better but does not
396 handle markers. We have to hand off any blocks with markers to the
401 register int c0, c1; \
402 c0 = GETJOCTET(*buffer++); \
403 c1 = GETJOCTET(*buffer); \
404 /* Pre-execute most common case */ \
405 get_buffer = (get_buffer << 8) | c0; \
408 /* Pre-execute case of FF/00, which represents an FF data byte */ \
411 /* Oops, it's actually a marker indicating end of compressed data. */ \
412 cinfo->unread_marker = c1; \
413 /* Back out pre-execution and fill the buffer with zero bits */ \
415 get_buffer &= ~0xFF; \
420 #if __WORDSIZE == 64 || defined(_WIN64)
422 /* Pre-fetch 48 bytes, because the holding register is 64-bit */
423 #define FILL_BIT_BUFFER_FAST \
424 if (bits_left < 16) { \
425 GET_BYTE GET_BYTE GET_BYTE GET_BYTE GET_BYTE GET_BYTE \
430 /* Pre-fetch 16 bytes, because the holding register is 32-bit */
431 #define FILL_BIT_BUFFER_FAST \
432 if (bits_left < 16) { \
440 * Out-of-line code for Huffman code decoding.
441 * See jdhuff.h for info about usage.
445 jpeg_huff_decode (bitread_working_state * state,
446 register bit_buf_type get_buffer, register int bits_left,
447 d_derived_tbl * htbl, int min_bits)
449 register int l = min_bits;
452 /* HUFF_DECODE has determined that the code is at least min_bits */
453 /* bits long, so fetch that many bits in one swoop. */
455 CHECK_BIT_BUFFER(*state, l, return -1);
458 /* Collect the rest of the Huffman code one bit at a time. */
459 /* This is per Figure F.16 in the JPEG spec. */
461 while (code > htbl->maxcode[l]) {
463 CHECK_BIT_BUFFER(*state, 1, return -1);
468 /* Unload the local registers */
469 state->get_buffer = get_buffer;
470 state->bits_left = bits_left;
472 /* With garbage input we may reach the sentinel value l = 17. */
475 WARNMS(state->cinfo, JWRN_HUFF_BAD_CODE);
476 return 0; /* fake a zero as the safest result */
479 return htbl->pub->huffval[ (int) (code + htbl->valoffset[l]) ];
484 * Figure F.12: extend sign bit.
485 * On some machines, a shift and add will be faster than a table lookup.
491 #define HUFF_EXTEND(x,s) ((x) + ((((x) - (1<<((s)-1))) >> 31) & (((-1)<<(s)) + 1)))
495 #define HUFF_EXTEND(x,s) ((x) < extend_test[s] ? (x) + extend_offset[s] : (x))
497 static const int extend_test[16] = /* entry n is 2**(n-1) */
498 { 0, 0x0001, 0x0002, 0x0004, 0x0008, 0x0010, 0x0020, 0x0040, 0x0080,
499 0x0100, 0x0200, 0x0400, 0x0800, 0x1000, 0x2000, 0x4000 };
501 static const int extend_offset[16] = /* entry n is (-1 << n) + 1 */
502 { 0, ((-1)<<1) + 1, ((-1)<<2) + 1, ((-1)<<3) + 1, ((-1)<<4) + 1,
503 ((-1)<<5) + 1, ((-1)<<6) + 1, ((-1)<<7) + 1, ((-1)<<8) + 1,
504 ((-1)<<9) + 1, ((-1)<<10) + 1, ((-1)<<11) + 1, ((-1)<<12) + 1,
505 ((-1)<<13) + 1, ((-1)<<14) + 1, ((-1)<<15) + 1 };
507 #endif /* AVOID_TABLES */
511 * Check for a restart marker & resynchronize decoder.
512 * Returns FALSE if must suspend.
516 process_restart (j_decompress_ptr cinfo)
518 huff_entropy_ptr entropy = (huff_entropy_ptr) cinfo->entropy;
521 /* Throw away any unused bits remaining in bit buffer; */
522 /* include any full bytes in next_marker's count of discarded bytes */
523 cinfo->marker->discarded_bytes += entropy->bitstate.bits_left / 8;
524 entropy->bitstate.bits_left = 0;
526 /* Advance past the RSTn marker */
527 if (! (*cinfo->marker->read_restart_marker) (cinfo))
530 /* Re-initialize DC predictions to 0 */
531 for (ci = 0; ci < cinfo->comps_in_scan; ci++)
532 entropy->saved.last_dc_val[ci] = 0;
534 /* Reset restart counter */
535 entropy->restarts_to_go = cinfo->restart_interval;
537 /* Reset out-of-data flag, unless read_restart_marker left us smack up
538 * against a marker. In that case we will end up treating the next data
539 * segment as empty, and we can avoid producing bogus output pixels by
540 * leaving the flag set.
542 if (cinfo->unread_marker == 0)
543 entropy->pub.insufficient_data = FALSE;
550 decode_mcu_slow (j_decompress_ptr cinfo, JBLOCKROW *MCU_data)
552 huff_entropy_ptr entropy = (huff_entropy_ptr) cinfo->entropy;
556 /* Outer loop handles each block in the MCU */
558 /* Load up working state */
559 BITREAD_LOAD_STATE(cinfo,entropy->bitstate);
560 ASSIGN_STATE(state, entropy->saved);
562 for (blkn = 0; blkn < cinfo->blocks_in_MCU; blkn++) {
563 JBLOCKROW block = MCU_data[blkn];
564 d_derived_tbl * dctbl = entropy->dc_cur_tbls[blkn];
565 d_derived_tbl * actbl = entropy->ac_cur_tbls[blkn];
566 register int s, k, r;
568 /* Decode a single block's worth of coefficients */
570 /* Section F.2.2.1: decode the DC coefficient difference */
571 HUFF_DECODE(s, br_state, dctbl, return FALSE, label1);
573 CHECK_BIT_BUFFER(br_state, s, return FALSE);
575 s = HUFF_EXTEND(r, s);
578 if (entropy->dc_needed[blkn]) {
579 /* Convert DC difference to actual value, update last_dc_val */
580 int ci = cinfo->MCU_membership[blkn];
581 s += state.last_dc_val[ci];
582 state.last_dc_val[ci] = s;
583 /* Output the DC coefficient (assumes jpeg_natural_order[0] = 0) */
584 (*block)[0] = (JCOEF) s;
587 if (entropy->ac_needed[blkn]) {
589 /* Section F.2.2.2: decode the AC coefficients */
590 /* Since zeroes are skipped, output area must be cleared beforehand */
591 for (k = 1; k < DCTSIZE2; k++) {
592 HUFF_DECODE(s, br_state, actbl, return FALSE, label2);
599 CHECK_BIT_BUFFER(br_state, s, return FALSE);
601 s = HUFF_EXTEND(r, s);
602 /* Output coefficient in natural (dezigzagged) order.
603 * Note: the extra entries in jpeg_natural_order[] will save us
604 * if k >= DCTSIZE2, which could happen if the data is corrupted.
606 (*block)[jpeg_natural_order[k]] = (JCOEF) s;
616 /* Section F.2.2.2: decode the AC coefficients */
617 /* In this path we just discard the values */
618 for (k = 1; k < DCTSIZE2; k++) {
619 HUFF_DECODE(s, br_state, actbl, return FALSE, label3);
626 CHECK_BIT_BUFFER(br_state, s, return FALSE);
637 /* Completed MCU, so update state */
638 BITREAD_SAVE_STATE(cinfo,entropy->bitstate);
639 ASSIGN_STATE(entropy->saved, state);
645 decode_mcu_fast (j_decompress_ptr cinfo, JBLOCKROW *MCU_data)
647 huff_entropy_ptr entropy = (huff_entropy_ptr) cinfo->entropy;
652 /* Outer loop handles each block in the MCU */
654 /* Load up working state */
655 BITREAD_LOAD_STATE(cinfo,entropy->bitstate);
656 buffer = (JOCTET *) br_state.next_input_byte;
657 ASSIGN_STATE(state, entropy->saved);
659 for (blkn = 0; blkn < cinfo->blocks_in_MCU; blkn++) {
660 JBLOCKROW block = MCU_data[blkn];
661 d_derived_tbl * dctbl = entropy->dc_cur_tbls[blkn];
662 d_derived_tbl * actbl = entropy->ac_cur_tbls[blkn];
663 register int s, k, r, l;
665 HUFF_DECODE_FAST(s, l, dctbl);
669 s = HUFF_EXTEND(r, s);
672 if (entropy->dc_needed[blkn]) {
673 int ci = cinfo->MCU_membership[blkn];
674 s += state.last_dc_val[ci];
675 state.last_dc_val[ci] = s;
676 (*block)[0] = (JCOEF) s;
679 if (entropy->ac_needed[blkn]) {
681 for (k = 1; k < DCTSIZE2; k++) {
682 HUFF_DECODE_FAST(s, l, actbl);
690 s = HUFF_EXTEND(r, s);
691 (*block)[jpeg_natural_order[k]] = (JCOEF) s;
700 for (k = 1; k < DCTSIZE2; k++) {
701 HUFF_DECODE_FAST(s, l, actbl);
717 if (cinfo->unread_marker != 0) {
718 cinfo->unread_marker = 0;
722 br_state.bytes_in_buffer -= (buffer - br_state.next_input_byte);
723 br_state.next_input_byte = buffer;
724 BITREAD_SAVE_STATE(cinfo,entropy->bitstate);
725 ASSIGN_STATE(entropy->saved, state);
731 * Decode and return one MCU's worth of Huffman-compressed coefficients.
732 * The coefficients are reordered from zigzag order into natural array order,
733 * but are not dequantized.
735 * The i'th block of the MCU is stored into the block pointed to by
736 * MCU_data[i]. WE ASSUME THIS AREA HAS BEEN ZEROED BY THE CALLER.
737 * (Wholesale zeroing is usually a little faster than retail...)
739 * Returns FALSE if data source requested suspension. In that case no
740 * changes have been made to permanent state. (Exception: some output
741 * coefficients may already have been assigned. This is harmless for
742 * this module, since we'll just re-assign them on the next call.)
745 #define BUFSIZE (DCTSIZE2 * 2)
748 decode_mcu (j_decompress_ptr cinfo, JBLOCKROW *MCU_data)
750 huff_entropy_ptr entropy = (huff_entropy_ptr) cinfo->entropy;
753 /* Process restart marker if needed; may have to suspend */
754 if (cinfo->restart_interval) {
755 if (entropy->restarts_to_go == 0)
756 if (! process_restart(cinfo))
761 if (cinfo->src->bytes_in_buffer < BUFSIZE * (size_t)cinfo->blocks_in_MCU
762 || cinfo->unread_marker != 0)
765 /* If we've run out of data, just leave the MCU set to zeroes.
766 * This way, we return uniform gray for the remainder of the segment.
768 if (! entropy->pub.insufficient_data) {
771 if (!decode_mcu_fast(cinfo, MCU_data)) goto use_slow;
775 if (!decode_mcu_slow(cinfo, MCU_data)) return FALSE;
780 /* Account for restart interval (no-op if not using restarts) */
781 entropy->restarts_to_go--;
788 * Module initialization routine for Huffman entropy decoding.
792 jinit_huff_decoder (j_decompress_ptr cinfo)
794 huff_entropy_ptr entropy;
797 entropy = (huff_entropy_ptr)
798 (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE,
799 SIZEOF(huff_entropy_decoder));
800 cinfo->entropy = (struct jpeg_entropy_decoder *) entropy;
801 entropy->pub.start_pass = start_pass_huff_decoder;
802 entropy->pub.decode_mcu = decode_mcu;
804 /* Mark tables unallocated */
805 for (i = 0; i < NUM_HUFF_TBLS; i++) {
806 entropy->dc_derived_tbls[i] = entropy->ac_derived_tbls[i] = NULL;