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, 2016, 2018, D. R. Commander.
8 * For conditions of distribution and use, see the accompanying README.ijg
11 * This file contains Huffman entropy decoding routines.
13 * Much of the complexity here has to do with supporting input suspension.
14 * If the data source module demands suspension, we want to be able to back
15 * up to the start of the current MCU. To do this, we copy state variables
16 * into local working storage, and update them back to the permanent
17 * storage only upon successful completion of an MCU.
19 * NOTE: All referenced figures are from
20 * Recommendation ITU-T T.81 (1992) | ISO/IEC 10918-1:1994.
23 #define JPEG_INTERNALS
26 #include "jdhuff.h" /* Declarations shared with jdphuff.c */
32 * Expanded entropy decoder object for Huffman decoding.
34 * The savable_state subrecord contains fields that change within an MCU,
35 * but must not be updated permanently until we complete the MCU.
39 int last_dc_val
[MAX_COMPS_IN_SCAN
]; /* last DC coef for each component */
42 /* This macro is to work around compilers with missing or broken
43 * structure assignment. You'll need to fix this code if you have
44 * such a compiler and you change MAX_COMPS_IN_SCAN.
47 #ifndef NO_STRUCT_ASSIGN
48 #define ASSIGN_STATE(dest, src) ((dest) = (src))
50 #if MAX_COMPS_IN_SCAN == 4
51 #define ASSIGN_STATE(dest, src) \
52 ((dest).last_dc_val[0] = (src).last_dc_val[0], \
53 (dest).last_dc_val[1] = (src).last_dc_val[1], \
54 (dest).last_dc_val[2] = (src).last_dc_val[2], \
55 (dest).last_dc_val[3] = (src).last_dc_val[3])
61 struct jpeg_entropy_decoder pub
; /* public fields */
63 /* These fields are loaded into local variables at start of each MCU.
64 * In case of suspension, we exit WITHOUT updating them.
66 bitread_perm_state bitstate
; /* Bit buffer at start of MCU */
67 savable_state saved
; /* Other state at start of MCU */
69 /* These fields are NOT loaded into local working state. */
70 unsigned int restarts_to_go
; /* MCUs left in this restart interval */
72 /* Pointers to derived tables (these workspaces have image lifespan) */
73 d_derived_tbl
*dc_derived_tbls
[NUM_HUFF_TBLS
];
74 d_derived_tbl
*ac_derived_tbls
[NUM_HUFF_TBLS
];
76 /* Precalculated info set up by start_pass for use in decode_mcu: */
78 /* Pointers to derived tables to be used for each block within an MCU */
79 d_derived_tbl
*dc_cur_tbls
[D_MAX_BLOCKS_IN_MCU
];
80 d_derived_tbl
*ac_cur_tbls
[D_MAX_BLOCKS_IN_MCU
];
81 /* Whether we care about the DC and AC coefficient values for each block */
82 boolean dc_needed
[D_MAX_BLOCKS_IN_MCU
];
83 boolean ac_needed
[D_MAX_BLOCKS_IN_MCU
];
84 } huff_entropy_decoder
;
86 typedef huff_entropy_decoder
*huff_entropy_ptr
;
90 * Initialize for a Huffman-compressed scan.
94 start_pass_huff_decoder(j_decompress_ptr cinfo
)
96 huff_entropy_ptr entropy
= (huff_entropy_ptr
)cinfo
->entropy
;
97 int ci
, blkn
, dctbl
, actbl
;
98 d_derived_tbl
**pdtbl
;
99 jpeg_component_info
*compptr
;
101 /* Check that the scan parameters Ss, Se, Ah/Al are OK for sequential JPEG.
102 * This ought to be an error condition, but we make it a warning because
103 * there are some baseline files out there with all zeroes in these bytes.
105 if (cinfo
->Ss
!= 0 || cinfo
->Se
!= DCTSIZE2
- 1 ||
106 cinfo
->Ah
!= 0 || cinfo
->Al
!= 0)
107 WARNMS(cinfo
, JWRN_NOT_SEQUENTIAL
);
109 for (ci
= 0; ci
< cinfo
->comps_in_scan
; ci
++) {
110 compptr
= cinfo
->cur_comp_info
[ci
];
111 dctbl
= compptr
->dc_tbl_no
;
112 actbl
= compptr
->ac_tbl_no
;
113 /* Compute derived values for Huffman tables */
114 /* We may do this more than once for a table, but it's not expensive */
115 pdtbl
= (d_derived_tbl
**)(entropy
->dc_derived_tbls
) + dctbl
;
116 jpeg_make_d_derived_tbl(cinfo
, TRUE
, dctbl
, pdtbl
);
117 pdtbl
= (d_derived_tbl
**)(entropy
->ac_derived_tbls
) + actbl
;
118 jpeg_make_d_derived_tbl(cinfo
, FALSE
, actbl
, pdtbl
);
119 /* Initialize DC predictions to 0 */
120 entropy
->saved
.last_dc_val
[ci
] = 0;
123 /* Precalculate decoding info for each block in an MCU of this scan */
124 for (blkn
= 0; blkn
< cinfo
->blocks_in_MCU
; blkn
++) {
125 ci
= cinfo
->MCU_membership
[blkn
];
126 compptr
= cinfo
->cur_comp_info
[ci
];
127 /* Precalculate which table to use for each block */
128 entropy
->dc_cur_tbls
[blkn
] = entropy
->dc_derived_tbls
[compptr
->dc_tbl_no
];
129 entropy
->ac_cur_tbls
[blkn
] = entropy
->ac_derived_tbls
[compptr
->ac_tbl_no
];
130 /* Decide whether we really care about the coefficient values */
131 if (compptr
->component_needed
) {
132 entropy
->dc_needed
[blkn
] = TRUE
;
133 /* we don't need the ACs if producing a 1/8th-size image */
134 entropy
->ac_needed
[blkn
] = (compptr
->_DCT_scaled_size
> 1);
136 entropy
->dc_needed
[blkn
] = entropy
->ac_needed
[blkn
] = FALSE
;
140 /* Initialize bitread state variables */
141 entropy
->bitstate
.bits_left
= 0;
142 entropy
->bitstate
.get_buffer
= 0; /* unnecessary, but keeps Purify quiet */
143 entropy
->pub
.insufficient_data
= FALSE
;
145 /* Initialize restart counter */
146 entropy
->restarts_to_go
= cinfo
->restart_interval
;
151 * Compute the derived values for a Huffman table.
152 * This routine also performs some validation checks on the table.
154 * Note this is also used by jdphuff.c.
158 jpeg_make_d_derived_tbl(j_decompress_ptr cinfo
, boolean isDC
, int tblno
,
159 d_derived_tbl
**pdtbl
)
163 int p
, i
, l
, si
, numsymbols
;
166 unsigned int huffcode
[257];
169 /* Note that huffsize[] and huffcode[] are filled in code-length order,
170 * paralleling the order of the symbols themselves in htbl->huffval[].
173 /* Find the input Huffman table */
174 if (tblno
< 0 || tblno
>= NUM_HUFF_TBLS
)
175 ERREXIT1(cinfo
, JERR_NO_HUFF_TABLE
, tblno
);
177 isDC
? cinfo
->dc_huff_tbl_ptrs
[tblno
] : cinfo
->ac_huff_tbl_ptrs
[tblno
];
179 ERREXIT1(cinfo
, JERR_NO_HUFF_TABLE
, tblno
);
181 /* Allocate a workspace if we haven't already done so. */
183 *pdtbl
= (d_derived_tbl
*)
184 (*cinfo
->mem
->alloc_small
) ((j_common_ptr
)cinfo
, JPOOL_IMAGE
,
185 sizeof(d_derived_tbl
));
187 dtbl
->pub
= htbl
; /* fill in back link */
189 /* Figure C.1: make table of Huffman code length for each symbol */
192 for (l
= 1; l
<= 16; l
++) {
193 i
= (int)htbl
->bits
[l
];
194 if (i
< 0 || p
+ i
> 256) /* protect against table overrun */
195 ERREXIT(cinfo
, JERR_BAD_HUFF_TABLE
);
197 huffsize
[p
++] = (char)l
;
202 /* Figure C.2: generate the codes themselves */
203 /* We also validate that the counts represent a legal Huffman code tree. */
208 while (huffsize
[p
]) {
209 while (((int)huffsize
[p
]) == si
) {
210 huffcode
[p
++] = code
;
213 /* code is now 1 more than the last code used for codelength si; but
214 * it must still fit in si bits, since no code is allowed to be all ones.
216 if (((JLONG
)code
) >= (((JLONG
)1) << si
))
217 ERREXIT(cinfo
, JERR_BAD_HUFF_TABLE
);
222 /* Figure F.15: generate decoding tables for bit-sequential decoding */
225 for (l
= 1; l
<= 16; l
++) {
227 /* valoffset[l] = huffval[] index of 1st symbol of code length l,
228 * minus the minimum code of length l
230 dtbl
->valoffset
[l
] = (JLONG
)p
- (JLONG
)huffcode
[p
];
232 dtbl
->maxcode
[l
] = huffcode
[p
- 1]; /* maximum code of length l */
234 dtbl
->maxcode
[l
] = -1; /* -1 if no codes of this length */
237 dtbl
->valoffset
[17] = 0;
238 dtbl
->maxcode
[17] = 0xFFFFFL
; /* ensures jpeg_huff_decode terminates */
240 /* Compute lookahead tables to speed up decoding.
241 * First we set all the table entries to 0, indicating "too long";
242 * then we iterate through the Huffman codes that are short enough and
243 * fill in all the entries that correspond to bit sequences starting
247 for (i
= 0; i
< (1 << HUFF_LOOKAHEAD
); i
++)
248 dtbl
->lookup
[i
] = (HUFF_LOOKAHEAD
+ 1) << HUFF_LOOKAHEAD
;
251 for (l
= 1; l
<= HUFF_LOOKAHEAD
; l
++) {
252 for (i
= 1; i
<= (int)htbl
->bits
[l
]; i
++, p
++) {
253 /* l = current code's length, p = its index in huffcode[] & huffval[]. */
254 /* Generate left-justified code followed by all possible bit sequences */
255 lookbits
= huffcode
[p
] << (HUFF_LOOKAHEAD
- l
);
256 for (ctr
= 1 << (HUFF_LOOKAHEAD
- l
); ctr
> 0; ctr
--) {
257 dtbl
->lookup
[lookbits
] = (l
<< HUFF_LOOKAHEAD
) | htbl
->huffval
[p
];
263 /* Validate symbols as being reasonable.
264 * For AC tables, we make no check, but accept all byte values 0..255.
265 * For DC tables, we require the symbols to be in range 0..15.
266 * (Tighter bounds could be applied depending on the data depth and mode,
267 * but this is sufficient to ensure safe decoding.)
270 for (i
= 0; i
< numsymbols
; i
++) {
271 int sym
= htbl
->huffval
[i
];
272 if (sym
< 0 || sym
> 15)
273 ERREXIT(cinfo
, JERR_BAD_HUFF_TABLE
);
280 * Out-of-line code for bit fetching (shared with jdphuff.c).
281 * See jdhuff.h for info about usage.
282 * Note: current values of get_buffer and bits_left are passed as parameters,
283 * but are returned in the corresponding fields of the state struct.
285 * On most machines MIN_GET_BITS should be 25 to allow the full 32-bit width
286 * of get_buffer to be used. (On machines with wider words, an even larger
287 * buffer could be used.) However, on some machines 32-bit shifts are
288 * quite slow and take time proportional to the number of places shifted.
289 * (This is true with most PC compilers, for instance.) In this case it may
290 * be a win to set MIN_GET_BITS to the minimum value of 15. This reduces the
291 * average shift distance at the cost of more calls to jpeg_fill_bit_buffer.
295 #define MIN_GET_BITS 15 /* minimum allowable value */
297 #define MIN_GET_BITS (BIT_BUF_SIZE - 7)
302 jpeg_fill_bit_buffer(bitread_working_state
*state
,
303 register bit_buf_type get_buffer
, register int bits_left
,
305 /* Load up the bit buffer to a depth of at least nbits */
307 /* Copy heavily used state fields into locals (hopefully registers) */
308 register const JOCTET
*next_input_byte
= state
->next_input_byte
;
309 register size_t bytes_in_buffer
= state
->bytes_in_buffer
;
310 j_decompress_ptr cinfo
= state
->cinfo
;
312 /* Attempt to load at least MIN_GET_BITS bits into get_buffer. */
313 /* (It is assumed that no request will be for more than that many bits.) */
314 /* We fail to do so only if we hit a marker or are forced to suspend. */
316 if (cinfo
->unread_marker
== 0) { /* cannot advance past a marker */
317 while (bits_left
< MIN_GET_BITS
) {
320 /* Attempt to read a byte */
321 if (bytes_in_buffer
== 0) {
322 if (!(*cinfo
->src
->fill_input_buffer
) (cinfo
))
324 next_input_byte
= cinfo
->src
->next_input_byte
;
325 bytes_in_buffer
= cinfo
->src
->bytes_in_buffer
;
328 c
= GETJOCTET(*next_input_byte
++);
330 /* If it's 0xFF, check and discard stuffed zero byte */
332 /* Loop here to discard any padding FF's on terminating marker,
333 * so that we can save a valid unread_marker value. NOTE: we will
334 * accept multiple FF's followed by a 0 as meaning a single FF data
335 * byte. This data pattern is not valid according to the standard.
338 if (bytes_in_buffer
== 0) {
339 if (!(*cinfo
->src
->fill_input_buffer
) (cinfo
))
341 next_input_byte
= cinfo
->src
->next_input_byte
;
342 bytes_in_buffer
= cinfo
->src
->bytes_in_buffer
;
345 c
= GETJOCTET(*next_input_byte
++);
349 /* Found FF/00, which represents an FF data byte */
352 /* Oops, it's actually a marker indicating end of compressed data.
353 * Save the marker code for later use.
354 * Fine point: it might appear that we should save the marker into
355 * bitread working state, not straight into permanent state. But
356 * once we have hit a marker, we cannot need to suspend within the
357 * current MCU, because we will read no more bytes from the data
358 * source. So it is OK to update permanent state right away.
360 cinfo
->unread_marker
= c
;
361 /* See if we need to insert some fake zero bits. */
366 /* OK, load c into get_buffer */
367 get_buffer
= (get_buffer
<< 8) | c
;
372 /* We get here if we've read the marker that terminates the compressed
373 * data segment. There should be enough bits in the buffer register
374 * to satisfy the request; if so, no problem.
376 if (nbits
> bits_left
) {
377 /* Uh-oh. Report corrupted data to user and stuff zeroes into
378 * the data stream, so that we can produce some kind of image.
379 * We use a nonvolatile flag to ensure that only one warning message
380 * appears per data segment.
382 if (!cinfo
->entropy
->insufficient_data
) {
383 WARNMS(cinfo
, JWRN_HIT_MARKER
);
384 cinfo
->entropy
->insufficient_data
= TRUE
;
386 /* Fill the buffer with zero bits */
387 get_buffer
<<= MIN_GET_BITS
- bits_left
;
388 bits_left
= MIN_GET_BITS
;
392 /* Unload the local registers */
393 state
->next_input_byte
= next_input_byte
;
394 state
->bytes_in_buffer
= bytes_in_buffer
;
395 state
->get_buffer
= get_buffer
;
396 state
->bits_left
= bits_left
;
402 /* Macro version of the above, which performs much better but does not
403 handle markers. We have to hand off any blocks with markers to the
407 register int c0, c1; \
408 c0 = GETJOCTET(*buffer++); \
409 c1 = GETJOCTET(*buffer); \
410 /* Pre-execute most common case */ \
411 get_buffer = (get_buffer << 8) | c0; \
414 /* Pre-execute case of FF/00, which represents an FF data byte */ \
417 /* Oops, it's actually a marker indicating end of compressed data. */ \
418 cinfo->unread_marker = c1; \
419 /* Back out pre-execution and fill the buffer with zero bits */ \
421 get_buffer &= ~0xFF; \
426 #if SIZEOF_SIZE_T == 8 || defined(_WIN64)
428 /* Pre-fetch 48 bytes, because the holding register is 64-bit */
429 #define FILL_BIT_BUFFER_FAST \
430 if (bits_left <= 16) { \
431 GET_BYTE GET_BYTE GET_BYTE GET_BYTE GET_BYTE GET_BYTE \
436 /* Pre-fetch 16 bytes, because the holding register is 32-bit */
437 #define FILL_BIT_BUFFER_FAST \
438 if (bits_left <= 16) { \
446 * Out-of-line code for Huffman code decoding.
447 * See jdhuff.h for info about usage.
451 jpeg_huff_decode(bitread_working_state
*state
,
452 register bit_buf_type get_buffer
, register int bits_left
,
453 d_derived_tbl
*htbl
, int min_bits
)
455 register int l
= min_bits
;
458 /* HUFF_DECODE has determined that the code is at least min_bits */
459 /* bits long, so fetch that many bits in one swoop. */
461 CHECK_BIT_BUFFER(*state
, l
, return -1);
464 /* Collect the rest of the Huffman code one bit at a time. */
465 /* This is per Figure F.16. */
467 while (code
> htbl
->maxcode
[l
]) {
469 CHECK_BIT_BUFFER(*state
, 1, return -1);
474 /* Unload the local registers */
475 state
->get_buffer
= get_buffer
;
476 state
->bits_left
= bits_left
;
478 /* With garbage input we may reach the sentinel value l = 17. */
481 WARNMS(state
->cinfo
, JWRN_HUFF_BAD_CODE
);
482 return 0; /* fake a zero as the safest result */
485 return htbl
->pub
->huffval
[(int)(code
+ htbl
->valoffset
[l
])];
490 * Figure F.12: extend sign bit.
491 * On some machines, a shift and add will be faster than a table lookup.
497 #define NEG_1 ((unsigned int)-1)
498 #define HUFF_EXTEND(x, s) \
499 ((x) + ((((x) - (1 << ((s) - 1))) >> 31) & (((NEG_1) << (s)) + 1)))
503 #define HUFF_EXTEND(x, s) \
504 ((x) < extend_test[s] ? (x) + extend_offset[s] : (x))
506 static const int extend_test
[16] = { /* entry n is 2**(n-1) */
507 0, 0x0001, 0x0002, 0x0004, 0x0008, 0x0010, 0x0020, 0x0040, 0x0080,
508 0x0100, 0x0200, 0x0400, 0x0800, 0x1000, 0x2000, 0x4000
511 static const int extend_offset
[16] = { /* entry n is (-1 << n) + 1 */
512 0, ((-1) << 1) + 1, ((-1) << 2) + 1, ((-1) << 3) + 1, ((-1) << 4) + 1,
513 ((-1) << 5) + 1, ((-1) << 6) + 1, ((-1) << 7) + 1, ((-1) << 8) + 1,
514 ((-1) << 9) + 1, ((-1) << 10) + 1, ((-1) << 11) + 1, ((-1) << 12) + 1,
515 ((-1) << 13) + 1, ((-1) << 14) + 1, ((-1) << 15) + 1
518 #endif /* AVOID_TABLES */
522 * Check for a restart marker & resynchronize decoder.
523 * Returns FALSE if must suspend.
527 process_restart(j_decompress_ptr cinfo
)
529 huff_entropy_ptr entropy
= (huff_entropy_ptr
)cinfo
->entropy
;
532 /* Throw away any unused bits remaining in bit buffer; */
533 /* include any full bytes in next_marker's count of discarded bytes */
534 cinfo
->marker
->discarded_bytes
+= entropy
->bitstate
.bits_left
/ 8;
535 entropy
->bitstate
.bits_left
= 0;
537 /* Advance past the RSTn marker */
538 if (!(*cinfo
->marker
->read_restart_marker
) (cinfo
))
541 /* Re-initialize DC predictions to 0 */
542 for (ci
= 0; ci
< cinfo
->comps_in_scan
; ci
++)
543 entropy
->saved
.last_dc_val
[ci
] = 0;
545 /* Reset restart counter */
546 entropy
->restarts_to_go
= cinfo
->restart_interval
;
548 /* Reset out-of-data flag, unless read_restart_marker left us smack up
549 * against a marker. In that case we will end up treating the next data
550 * segment as empty, and we can avoid producing bogus output pixels by
551 * leaving the flag set.
553 if (cinfo
->unread_marker
== 0)
554 entropy
->pub
.insufficient_data
= FALSE
;
561 decode_mcu_slow(j_decompress_ptr cinfo
, JBLOCKROW
*MCU_data
)
563 huff_entropy_ptr entropy
= (huff_entropy_ptr
)cinfo
->entropy
;
567 /* Outer loop handles each block in the MCU */
569 /* Load up working state */
570 BITREAD_LOAD_STATE(cinfo
, entropy
->bitstate
);
571 ASSIGN_STATE(state
, entropy
->saved
);
573 for (blkn
= 0; blkn
< cinfo
->blocks_in_MCU
; blkn
++) {
574 JBLOCKROW block
= MCU_data
? MCU_data
[blkn
] : NULL
;
575 d_derived_tbl
*dctbl
= entropy
->dc_cur_tbls
[blkn
];
576 d_derived_tbl
*actbl
= entropy
->ac_cur_tbls
[blkn
];
577 register int s
, k
, r
;
579 /* Decode a single block's worth of coefficients */
581 /* Section F.2.2.1: decode the DC coefficient difference */
582 HUFF_DECODE(s
, br_state
, dctbl
, return FALSE
, label1
);
584 CHECK_BIT_BUFFER(br_state
, s
, return FALSE
);
586 s
= HUFF_EXTEND(r
, s
);
589 if (entropy
->dc_needed
[blkn
]) {
590 /* Convert DC difference to actual value, update last_dc_val */
591 int ci
= cinfo
->MCU_membership
[blkn
];
592 s
+= state
.last_dc_val
[ci
];
593 state
.last_dc_val
[ci
] = s
;
595 /* Output the DC coefficient (assumes jpeg_natural_order[0] = 0) */
596 (*block
)[0] = (JCOEF
)s
;
600 if (entropy
->ac_needed
[blkn
] && block
) {
602 /* Section F.2.2.2: decode the AC coefficients */
603 /* Since zeroes are skipped, output area must be cleared beforehand */
604 for (k
= 1; k
< DCTSIZE2
; k
++) {
605 HUFF_DECODE(s
, br_state
, actbl
, return FALSE
, label2
);
612 CHECK_BIT_BUFFER(br_state
, s
, return FALSE
);
614 s
= HUFF_EXTEND(r
, s
);
615 /* Output coefficient in natural (dezigzagged) order.
616 * Note: the extra entries in jpeg_natural_order[] will save us
617 * if k >= DCTSIZE2, which could happen if the data is corrupted.
619 (*block
)[jpeg_natural_order
[k
]] = (JCOEF
)s
;
629 /* Section F.2.2.2: decode the AC coefficients */
630 /* In this path we just discard the values */
631 for (k
= 1; k
< DCTSIZE2
; k
++) {
632 HUFF_DECODE(s
, br_state
, actbl
, return FALSE
, label3
);
639 CHECK_BIT_BUFFER(br_state
, s
, return FALSE
);
650 /* Completed MCU, so update state */
651 BITREAD_SAVE_STATE(cinfo
, entropy
->bitstate
);
652 ASSIGN_STATE(entropy
->saved
, state
);
658 decode_mcu_fast(j_decompress_ptr cinfo
, JBLOCKROW
*MCU_data
)
660 huff_entropy_ptr entropy
= (huff_entropy_ptr
)cinfo
->entropy
;
665 /* Outer loop handles each block in the MCU */
667 /* Load up working state */
668 BITREAD_LOAD_STATE(cinfo
, entropy
->bitstate
);
669 buffer
= (JOCTET
*)br_state
.next_input_byte
;
670 ASSIGN_STATE(state
, entropy
->saved
);
672 for (blkn
= 0; blkn
< cinfo
->blocks_in_MCU
; blkn
++) {
673 JBLOCKROW block
= MCU_data
? MCU_data
[blkn
] : NULL
;
674 d_derived_tbl
*dctbl
= entropy
->dc_cur_tbls
[blkn
];
675 d_derived_tbl
*actbl
= entropy
->ac_cur_tbls
[blkn
];
676 register int s
, k
, r
, l
;
678 HUFF_DECODE_FAST(s
, l
, dctbl
, slow_decode_mcu
);
682 s
= HUFF_EXTEND(r
, s
);
685 if (entropy
->dc_needed
[blkn
]) {
686 int ci
= cinfo
->MCU_membership
[blkn
];
687 s
+= state
.last_dc_val
[ci
];
688 state
.last_dc_val
[ci
] = s
;
690 (*block
)[0] = (JCOEF
)s
;
693 if (entropy
->ac_needed
[blkn
] && block
) {
695 for (k
= 1; k
< DCTSIZE2
; k
++) {
696 HUFF_DECODE_FAST(s
, l
, actbl
, slow_decode_mcu
);
704 s
= HUFF_EXTEND(r
, s
);
705 (*block
)[jpeg_natural_order
[k
]] = (JCOEF
)s
;
714 for (k
= 1; k
< DCTSIZE2
; k
++) {
715 HUFF_DECODE_FAST(s
, l
, actbl
, slow_decode_mcu
);
731 if (cinfo
->unread_marker
!= 0) {
733 cinfo
->unread_marker
= 0;
737 br_state
.bytes_in_buffer
-= (buffer
- br_state
.next_input_byte
);
738 br_state
.next_input_byte
= buffer
;
739 BITREAD_SAVE_STATE(cinfo
, entropy
->bitstate
);
740 ASSIGN_STATE(entropy
->saved
, state
);
746 * Decode and return one MCU's worth of Huffman-compressed coefficients.
747 * The coefficients are reordered from zigzag order into natural array order,
748 * but are not dequantized.
750 * The i'th block of the MCU is stored into the block pointed to by
751 * MCU_data[i]. WE ASSUME THIS AREA HAS BEEN ZEROED BY THE CALLER.
752 * (Wholesale zeroing is usually a little faster than retail...)
754 * Returns FALSE if data source requested suspension. In that case no
755 * changes have been made to permanent state. (Exception: some output
756 * coefficients may already have been assigned. This is harmless for
757 * this module, since we'll just re-assign them on the next call.)
760 #define BUFSIZE (DCTSIZE2 * 8)
763 decode_mcu(j_decompress_ptr cinfo
, JBLOCKROW
*MCU_data
)
765 huff_entropy_ptr entropy
= (huff_entropy_ptr
)cinfo
->entropy
;
768 /* Process restart marker if needed; may have to suspend */
769 if (cinfo
->restart_interval
) {
770 if (entropy
->restarts_to_go
== 0)
771 if (!process_restart(cinfo
))
776 if (cinfo
->src
->bytes_in_buffer
< BUFSIZE
* (size_t)cinfo
->blocks_in_MCU
||
777 cinfo
->unread_marker
!= 0)
780 /* If we've run out of data, just leave the MCU set to zeroes.
781 * This way, we return uniform gray for the remainder of the segment.
783 if (!entropy
->pub
.insufficient_data
) {
786 if (!decode_mcu_fast(cinfo
, MCU_data
)) goto use_slow
;
789 if (!decode_mcu_slow(cinfo
, MCU_data
)) return FALSE
;
794 /* Account for restart interval (no-op if not using restarts) */
795 entropy
->restarts_to_go
--;
802 * Module initialization routine for Huffman entropy decoding.
806 jinit_huff_decoder(j_decompress_ptr cinfo
)
808 huff_entropy_ptr entropy
;
811 /* Motion JPEG frames typically do not include the Huffman tables if they
812 are the default tables. Thus, if the tables are not set by the time
813 the Huffman decoder is initialized (usually within the body of
814 jpeg_start_decompress()), we set them to default values. */
815 std_huff_tables((j_common_ptr
)cinfo
);
817 entropy
= (huff_entropy_ptr
)
818 (*cinfo
->mem
->alloc_small
) ((j_common_ptr
)cinfo
, JPOOL_IMAGE
,
819 sizeof(huff_entropy_decoder
));
820 cinfo
->entropy
= (struct jpeg_entropy_decoder
*)entropy
;
821 entropy
->pub
.start_pass
= start_pass_huff_decoder
;
822 entropy
->pub
.decode_mcu
= decode_mcu
;
824 /* Mark tables unallocated */
825 for (i
= 0; i
< NUM_HUFF_TBLS
; i
++) {
826 entropy
->dc_derived_tbls
[i
] = entropy
->ac_derived_tbls
[i
] = NULL
;