4
* Copyright (C) 1991-1997, 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
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], \
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(dest).last_dc_val[2] = (src).last_dc_val[2], \
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(dest).last_dc_val[3] = (src).last_dc_val[3])
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struct jpeg_entropy_decoder pub; /* public fields */
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/* These fields are loaded into local variables at start of each MCU.
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* In case of suspension, we exit WITHOUT updating them.
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bitread_perm_state bitstate; /* Bit buffer at start of MCU */
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savable_state saved; /* Other state at start of MCU */
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/* These fields are NOT loaded into local working state. */
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unsigned int restarts_to_go; /* MCUs left in this restart interval */
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/* Pointers to derived tables (these workspaces have image lifespan) */
65
d_derived_tbl * dc_derived_tbls[NUM_HUFF_TBLS];
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d_derived_tbl * ac_derived_tbls[NUM_HUFF_TBLS];
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/* Precalculated info set up by start_pass for use in decode_mcu: */
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/* Pointers to derived tables to be used for each block within an MCU */
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d_derived_tbl * dc_cur_tbls[D_MAX_BLOCKS_IN_MCU];
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d_derived_tbl * ac_cur_tbls[D_MAX_BLOCKS_IN_MCU];
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/* Whether we care about the DC and AC coefficient values for each block */
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boolean dc_needed[D_MAX_BLOCKS_IN_MCU];
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boolean ac_needed[D_MAX_BLOCKS_IN_MCU];
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} huff_entropy_decoder;
78
typedef huff_entropy_decoder * huff_entropy_ptr;
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* Initialize for a Huffman-compressed scan.
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start_pass_huff_decoder (j_decompress_ptr cinfo)
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huff_entropy_ptr entropy = (huff_entropy_ptr) cinfo->entropy;
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int ci, blkn, dctbl, actbl;
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jpeg_component_info * compptr;
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/* Check that the scan parameters Ss, Se, Ah/Al are OK for sequential JPEG.
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* This ought to be an error condition, but we make it a warning because
94
* there are some baseline files out there with all zeroes in these bytes.
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if (cinfo->Ss != 0 || cinfo->Se != DCTSIZE2-1 ||
97
cinfo->Ah != 0 || cinfo->Al != 0)
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WARNMS(cinfo, JWRN_NOT_SEQUENTIAL);
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for (ci = 0; ci < cinfo->comps_in_scan; ci++) {
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compptr = cinfo->cur_comp_info[ci];
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dctbl = compptr->dc_tbl_no;
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actbl = compptr->ac_tbl_no;
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/* Compute derived values for Huffman tables */
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/* We may do this more than once for a table, but it's not expensive */
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jpeg_make_d_derived_tbl(cinfo, TRUE, dctbl,
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& entropy->dc_derived_tbls[dctbl]);
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jpeg_make_d_derived_tbl(cinfo, FALSE, actbl,
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& entropy->ac_derived_tbls[actbl]);
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/* Initialize DC predictions to 0 */
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entropy->saved.last_dc_val[ci] = 0;
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/* Precalculate decoding info for each block in an MCU of this scan */
115
for (blkn = 0; blkn < cinfo->blocks_in_MCU; blkn++) {
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ci = cinfo->MCU_membership[blkn];
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compptr = cinfo->cur_comp_info[ci];
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/* Precalculate which table to use for each block */
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entropy->dc_cur_tbls[blkn] = entropy->dc_derived_tbls[compptr->dc_tbl_no];
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entropy->ac_cur_tbls[blkn] = entropy->ac_derived_tbls[compptr->ac_tbl_no];
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/* Decide whether we really care about the coefficient values */
122
if (compptr->component_needed) {
123
entropy->dc_needed[blkn] = TRUE;
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/* we don't need the ACs if producing a 1/8th-size image */
125
entropy->ac_needed[blkn] = (compptr->DCT_scaled_size > 1);
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entropy->dc_needed[blkn] = entropy->ac_needed[blkn] = FALSE;
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/* Initialize bitread state variables */
132
entropy->bitstate.bits_left = 0;
133
entropy->bitstate.get_buffer = 0; /* unnecessary, but keeps Purify quiet */
134
entropy->pub.insufficient_data = FALSE;
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/* Initialize restart counter */
137
entropy->restarts_to_go = cinfo->restart_interval;
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* Compute the derived values for a Huffman table.
143
* This routine also performs some validation checks on the table.
145
* Note this is also used by jdphuff.c.
149
jpeg_make_d_derived_tbl (j_decompress_ptr cinfo, boolean isDC, int tblno,
150
d_derived_tbl ** pdtbl)
154
int p, i, l, si, numsymbols;
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unsigned int huffcode[257];
160
/* Note that huffsize[] and huffcode[] are filled in code-length order,
161
* paralleling the order of the symbols themselves in htbl->huffval[].
164
/* Find the input Huffman table */
165
if (tblno < 0 || tblno >= NUM_HUFF_TBLS)
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ERREXIT1(cinfo, JERR_NO_HUFF_TABLE, tblno);
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isDC ? cinfo->dc_huff_tbl_ptrs[tblno] : cinfo->ac_huff_tbl_ptrs[tblno];
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ERREXIT1(cinfo, JERR_NO_HUFF_TABLE, tblno);
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/* Allocate a workspace if we haven't already done so. */
174
*pdtbl = (d_derived_tbl *)
175
(*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE,
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SIZEOF(d_derived_tbl));
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dtbl->pub = htbl; /* fill in back link */
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/* Figure C.1: make table of Huffman code length for each symbol */
183
for (l = 1; l <= 16; l++) {
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i = (int) htbl->bits[l];
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if (i < 0 || p + i > 256) /* protect against table overrun */
186
ERREXIT(cinfo, JERR_BAD_HUFF_TABLE);
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huffsize[p++] = (char) l;
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/* Figure C.2: generate the codes themselves */
194
/* We also validate that the counts represent a legal Huffman code tree. */
199
while (huffsize[p]) {
200
while (((int) huffsize[p]) == si) {
201
huffcode[p++] = code;
204
/* code is now 1 more than the last code used for codelength si; but
205
* it must still fit in si bits, since no code is allowed to be all ones.
207
if (((INT32) code) >= (((INT32) 1) << si))
208
ERREXIT(cinfo, JERR_BAD_HUFF_TABLE);
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/* Figure F.15: generate decoding tables for bit-sequential decoding */
216
for (l = 1; l <= 16; l++) {
218
/* valoffset[l] = huffval[] index of 1st symbol of code length l,
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* minus the minimum code of length l
221
dtbl->valoffset[l] = (INT32) p - (INT32) huffcode[p];
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dtbl->maxcode[l] = huffcode[p-1]; /* maximum code of length l */
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dtbl->maxcode[l] = -1; /* -1 if no codes of this length */
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dtbl->maxcode[17] = 0xFFFFFL; /* ensures jpeg_huff_decode terminates */
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/* Compute lookahead tables to speed up decoding.
231
* First we set all the table entries to 0, indicating "too long";
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* then we iterate through the Huffman codes that are short enough and
233
* fill in all the entries that correspond to bit sequences starting
237
MEMZERO(dtbl->look_nbits, SIZEOF(dtbl->look_nbits));
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for (l = 1; l <= HUFF_LOOKAHEAD; l++) {
241
for (i = 1; i <= (int) htbl->bits[l]; i++, p++) {
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/* l = current code's length, p = its index in huffcode[] & huffval[]. */
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/* Generate left-justified code followed by all possible bit sequences */
244
lookbits = huffcode[p] << (HUFF_LOOKAHEAD-l);
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for (ctr = 1 << (HUFF_LOOKAHEAD-l); ctr > 0; ctr--) {
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dtbl->look_nbits[lookbits] = l;
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dtbl->look_sym[lookbits] = htbl->huffval[p];
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/* Validate symbols as being reasonable.
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* For AC tables, we make no check, but accept all byte values 0..255.
255
* For DC tables, we require the symbols to be in range 0..15.
256
* (Tighter bounds could be applied depending on the data depth and mode,
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* but this is sufficient to ensure safe decoding.)
260
for (i = 0; i < numsymbols; i++) {
261
int sym = htbl->huffval[i];
262
if (sym < 0 || sym > 15)
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ERREXIT(cinfo, JERR_BAD_HUFF_TABLE);
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* Out-of-line code for bit fetching (shared with jdphuff.c).
271
* See jdhuff.h for info about usage.
272
* Note: current values of get_buffer and bits_left are passed as parameters,
273
* but are returned in the corresponding fields of the state struct.
275
* On most machines MIN_GET_BITS should be 25 to allow the full 32-bit width
276
* of get_buffer to be used. (On machines with wider words, an even larger
277
* buffer could be used.) However, on some machines 32-bit shifts are
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* quite slow and take time proportional to the number of places shifted.
279
* (This is true with most PC compilers, for instance.) In this case it may
280
* be a win to set MIN_GET_BITS to the minimum value of 15. This reduces the
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* average shift distance at the cost of more calls to jpeg_fill_bit_buffer.
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#define MIN_GET_BITS 15 /* minimum allowable value */
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#define MIN_GET_BITS (BIT_BUF_SIZE-7)
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jpeg_fill_bit_buffer (bitread_working_state * state,
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register bit_buf_type get_buffer, register int bits_left,
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/* Load up the bit buffer to a depth of at least nbits */
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/* Copy heavily used state fields into locals (hopefully registers) */
298
register const JOCTET * next_input_byte = state->next_input_byte;
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register size_t bytes_in_buffer = state->bytes_in_buffer;
300
j_decompress_ptr cinfo = state->cinfo;
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/* Attempt to load at least MIN_GET_BITS bits into get_buffer. */
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/* (It is assumed that no request will be for more than that many bits.) */
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/* We fail to do so only if we hit a marker or are forced to suspend. */
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if (cinfo->unread_marker == 0) { /* cannot advance past a marker */
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while (bits_left < MIN_GET_BITS) {
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/* Attempt to read a byte */
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if (bytes_in_buffer == 0) {
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if (! (*cinfo->src->fill_input_buffer) (cinfo))
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next_input_byte = cinfo->src->next_input_byte;
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bytes_in_buffer = cinfo->src->bytes_in_buffer;
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c = GETJOCTET(*next_input_byte++);
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/* If it's 0xFF, check and discard stuffed zero byte */
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/* Loop here to discard any padding FF's on terminating marker,
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* so that we can save a valid unread_marker value. NOTE: we will
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* accept multiple FF's followed by a 0 as meaning a single FF data
325
* byte. This data pattern is not valid according to the standard.
328
if (bytes_in_buffer == 0) {
329
if (! (*cinfo->src->fill_input_buffer) (cinfo))
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next_input_byte = cinfo->src->next_input_byte;
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bytes_in_buffer = cinfo->src->bytes_in_buffer;
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c = GETJOCTET(*next_input_byte++);
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/* Found FF/00, which represents an FF data byte */
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/* Oops, it's actually a marker indicating end of compressed data.
343
* Save the marker code for later use.
344
* Fine point: it might appear that we should save the marker into
345
* bitread working state, not straight into permanent state. But
346
* once we have hit a marker, we cannot need to suspend within the
347
* current MCU, because we will read no more bytes from the data
348
* source. So it is OK to update permanent state right away.
350
cinfo->unread_marker = c;
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/* See if we need to insert some fake zero bits. */
356
/* OK, load c into get_buffer */
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get_buffer = (get_buffer << 8) | c;
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/* We get here if we've read the marker that terminates the compressed
363
* data segment. There should be enough bits in the buffer register
364
* to satisfy the request; if so, no problem.
366
if (nbits > bits_left) {
367
/* Uh-oh. Report corrupted data to user and stuff zeroes into
368
* the data stream, so that we can produce some kind of image.
369
* We use a nonvolatile flag to ensure that only one warning message
370
* appears per data segment.
372
if (! cinfo->entropy->insufficient_data) {
373
WARNMS(cinfo, JWRN_HIT_MARKER);
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cinfo->entropy->insufficient_data = TRUE;
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/* Fill the buffer with zero bits */
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get_buffer <<= MIN_GET_BITS - bits_left;
378
bits_left = MIN_GET_BITS;
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/* Unload the local registers */
383
state->next_input_byte = next_input_byte;
384
state->bytes_in_buffer = bytes_in_buffer;
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state->get_buffer = get_buffer;
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state->bits_left = bits_left;
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* Out-of-line code for Huffman code decoding.
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* See jdhuff.h for info about usage.
398
jpeg_huff_decode (bitread_working_state * state,
399
register bit_buf_type get_buffer, register int bits_left,
400
d_derived_tbl * htbl, int min_bits)
402
register int l = min_bits;
405
/* HUFF_DECODE has determined that the code is at least min_bits */
406
/* bits long, so fetch that many bits in one swoop. */
408
CHECK_BIT_BUFFER(*state, l, return -1);
411
/* Collect the rest of the Huffman code one bit at a time. */
412
/* This is per Figure F.16 in the JPEG spec. */
414
while (code > htbl->maxcode[l]) {
416
CHECK_BIT_BUFFER(*state, 1, return -1);
421
/* Unload the local registers */
422
state->get_buffer = get_buffer;
423
state->bits_left = bits_left;
425
/* With garbage input we may reach the sentinel value l = 17. */
428
WARNMS(state->cinfo, JWRN_HUFF_BAD_CODE);
429
return 0; /* fake a zero as the safest result */
432
return htbl->pub->huffval[ (int) (code + htbl->valoffset[l]) ];
437
* Figure F.12: extend sign bit.
438
* On some machines, a shift and add will be faster than a table lookup.
443
#define HUFF_EXTEND(x,s) ((x) < (1<<((s)-1)) ? (x) + (((-1)<<(s)) + 1) : (x))
447
#define HUFF_EXTEND(x,s) ((x) < extend_test[s] ? (x) + extend_offset[s] : (x))
449
static const int extend_test[16] = /* entry n is 2**(n-1) */
450
{ 0, 0x0001, 0x0002, 0x0004, 0x0008, 0x0010, 0x0020, 0x0040, 0x0080,
451
0x0100, 0x0200, 0x0400, 0x0800, 0x1000, 0x2000, 0x4000 };
453
static const int extend_offset[16] = /* entry n is (-1 << n) + 1 */
454
{ 0, ((-1)<<1) + 1, ((-1)<<2) + 1, ((-1)<<3) + 1, ((-1)<<4) + 1,
455
((-1)<<5) + 1, ((-1)<<6) + 1, ((-1)<<7) + 1, ((-1)<<8) + 1,
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((-1)<<9) + 1, ((-1)<<10) + 1, ((-1)<<11) + 1, ((-1)<<12) + 1,
457
((-1)<<13) + 1, ((-1)<<14) + 1, ((-1)<<15) + 1 };
459
#endif /* AVOID_TABLES */
463
* Check for a restart marker & resynchronize decoder.
464
* Returns FALSE if must suspend.
468
process_restart (j_decompress_ptr cinfo)
470
huff_entropy_ptr entropy = (huff_entropy_ptr) cinfo->entropy;
473
/* Throw away any unused bits remaining in bit buffer; */
474
/* include any full bytes in next_marker's count of discarded bytes */
475
cinfo->marker->discarded_bytes += entropy->bitstate.bits_left / 8;
476
entropy->bitstate.bits_left = 0;
478
/* Advance past the RSTn marker */
479
if (! (*cinfo->marker->read_restart_marker) (cinfo))
482
/* Re-initialize DC predictions to 0 */
483
for (ci = 0; ci < cinfo->comps_in_scan; ci++)
484
entropy->saved.last_dc_val[ci] = 0;
486
/* Reset restart counter */
487
entropy->restarts_to_go = cinfo->restart_interval;
489
/* Reset out-of-data flag, unless read_restart_marker left us smack up
490
* against a marker. In that case we will end up treating the next data
491
* segment as empty, and we can avoid producing bogus output pixels by
492
* leaving the flag set.
494
if (cinfo->unread_marker == 0)
495
entropy->pub.insufficient_data = FALSE;
502
* Decode and return one MCU's worth of Huffman-compressed coefficients.
503
* The coefficients are reordered from zigzag order into natural array order,
504
* but are not dequantized.
506
* The i'th block of the MCU is stored into the block pointed to by
507
* MCU_data[i]. WE ASSUME THIS AREA HAS BEEN ZEROED BY THE CALLER.
508
* (Wholesale zeroing is usually a little faster than retail...)
510
* Returns FALSE if data source requested suspension. In that case no
511
* changes have been made to permanent state. (Exception: some output
512
* coefficients may already have been assigned. This is harmless for
513
* this module, since we'll just re-assign them on the next call.)
517
decode_mcu (j_decompress_ptr cinfo, JBLOCKROW *MCU_data)
519
huff_entropy_ptr entropy = (huff_entropy_ptr) cinfo->entropy;
524
/* Process restart marker if needed; may have to suspend */
525
if (cinfo->restart_interval) {
526
if (entropy->restarts_to_go == 0)
527
if (! process_restart(cinfo))
531
/* If we've run out of data, just leave the MCU set to zeroes.
532
* This way, we return uniform gray for the remainder of the segment.
534
if (! entropy->pub.insufficient_data) {
536
/* Load up working state */
537
BITREAD_LOAD_STATE(cinfo,entropy->bitstate);
538
ASSIGN_STATE(state, entropy->saved);
540
/* Outer loop handles each block in the MCU */
542
for (blkn = 0; blkn < cinfo->blocks_in_MCU; blkn++) {
543
JBLOCKROW block = MCU_data[blkn];
544
d_derived_tbl * dctbl = entropy->dc_cur_tbls[blkn];
545
d_derived_tbl * actbl = entropy->ac_cur_tbls[blkn];
546
register int s, k, r;
548
/* Decode a single block's worth of coefficients */
550
/* Section F.2.2.1: decode the DC coefficient difference */
551
HUFF_DECODE(s, br_state, dctbl, return FALSE, label1);
553
CHECK_BIT_BUFFER(br_state, s, return FALSE);
555
s = HUFF_EXTEND(r, s);
558
if (entropy->dc_needed[blkn]) {
559
/* Convert DC difference to actual value, update last_dc_val */
560
int ci = cinfo->MCU_membership[blkn];
561
s += state.last_dc_val[ci];
562
state.last_dc_val[ci] = s;
563
/* Output the DC coefficient (assumes jpeg_natural_order[0] = 0) */
564
(*block)[0] = (JCOEF) s;
567
if (entropy->ac_needed[blkn]) {
569
/* Section F.2.2.2: decode the AC coefficients */
570
/* Since zeroes are skipped, output area must be cleared beforehand */
571
for (k = 1; k < DCTSIZE2; k++) {
572
HUFF_DECODE(s, br_state, actbl, return FALSE, label2);
579
CHECK_BIT_BUFFER(br_state, s, return FALSE);
581
s = HUFF_EXTEND(r, s);
582
/* Output coefficient in natural (dezigzagged) order.
583
* Note: the extra entries in jpeg_natural_order[] will save us
584
* if k >= DCTSIZE2, which could happen if the data is corrupted.
586
(*block)[jpeg_natural_order[k]] = (JCOEF) s;
596
/* Section F.2.2.2: decode the AC coefficients */
597
/* In this path we just discard the values */
598
for (k = 1; k < DCTSIZE2; k++) {
599
HUFF_DECODE(s, br_state, actbl, return FALSE, label3);
606
CHECK_BIT_BUFFER(br_state, s, return FALSE);
618
/* Completed MCU, so update state */
619
BITREAD_SAVE_STATE(cinfo,entropy->bitstate);
620
ASSIGN_STATE(entropy->saved, state);
623
/* Account for restart interval (no-op if not using restarts) */
624
entropy->restarts_to_go--;
631
* Module initialization routine for Huffman entropy decoding.
635
jinit_huff_decoder (j_decompress_ptr cinfo)
637
huff_entropy_ptr entropy;
640
entropy = (huff_entropy_ptr)
641
(*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE,
642
SIZEOF(huff_entropy_decoder));
643
cinfo->entropy = (struct jpeg_entropy_decoder *) entropy;
644
entropy->pub.start_pass = start_pass_huff_decoder;
645
entropy->pub.decode_mcu = decode_mcu;
647
/* Mark tables unallocated */
648
for (i = 0; i < NUM_HUFF_TBLS; i++) {
649
entropy->dc_derived_tbls[i] = entropy->ac_derived_tbls[i] = NULL;