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/*
* jdhuff.c
*
* Copyright (C) 1991, 1992, 1993, Thomas G. Lane.
* This file is part of the Independent JPEG Group's software.
* For conditions of distribution and use, see the accompanying README file.
*
* This file contains Huffman entropy decoding routines.
* These routines are invoked via the methods entropy_decode
* and entropy_decode_init/term.
*/
#include "jinclude.h"
/* Static variables to avoid passing 'round extra parameters */
static decompress_info_ptr dcinfo;
static INT32 get_buffer; /* current bit-extraction buffer */
static int bits_left; /* # of unused bits in it */
static boolean printed_eod; /* flag to suppress multiple end-of-data msgs */
LOCAL void
fix_huff_tbl (HUFF_TBL * htbl)
/* Compute derived values for a Huffman table */
{
int p, i, l, si;
int lookbits, ctr;
char huffsize[257];
UINT16 huffcode[257];
UINT16 code;
/* Figure C.1: make table of Huffman code length for each symbol */
/* Note that this is in code-length order. */
p = 0;
for (l = 1; l <= 16; l++) {
for (i = 1; i <= (int) htbl->bits[l]; i++)
huffsize[p++] = (char) l;
}
huffsize[p] = 0;
/* Figure C.2: generate the codes themselves */
/* Note that this is in code-length order. */
code = 0;
si = huffsize[0];
p = 0;
while (huffsize[p]) {
while (((int) huffsize[p]) == si) {
huffcode[p++] = code;
code++;
}
code <<= 1;
si++;
}
/* Figure F.15: generate decoding tables for bit-sequential decoding */
p = 0;
for (l = 1; l <= 16; l++) {
if (htbl->bits[l]) {
htbl->priv.dec.valptr[l] = p; /* huffval[] index of 1st symbol of code length l */
htbl->priv.dec.mincode[l] = huffcode[p]; /* minimum code of length l */
p += htbl->bits[l];
htbl->priv.dec.maxcode[l] = huffcode[p-1]; /* maximum code of length l */
} else {
htbl->priv.dec.maxcode[l] = -1; /* -1 if no codes of this length */
}
}
htbl->priv.dec.maxcode[17] = 0xFFFFFL; /* ensures huff_DECODE terminates */
/* Compute lookahead tables to speed up decoding.
* First we set all the table entries to 0, indicating "too long";
* then we iterate through the Huffman codes that are short enough and
* fill in all the entries that correspond to bit sequences starting
* with that code.
*/
MEMZERO(htbl->priv.dec.look_nbits, SIZEOF(htbl->priv.dec.look_nbits));
p = 0;
for (l = 1; l <= HUFF_LOOKAHEAD; l++) {
for (i = 1; i <= (int) htbl->bits[l]; i++, p++) {
/* l = current code's length, p = its index in huffcode[] & huffval[]. */
/* Generate left-justified code followed by all possible bit sequences */
lookbits = huffcode[p] << (HUFF_LOOKAHEAD-l);
for (ctr = 1 << (HUFF_LOOKAHEAD-l); ctr > 0; ctr--) {
htbl->priv.dec.look_nbits[lookbits] = l;
htbl->priv.dec.look_sym[lookbits] = htbl->huffval[p];
lookbits++;
}
}
}
}
/*
* Code for extracting the next N bits from the input stream.
* (N never exceeds 15 for JPEG data.)
* This needs to go as fast as possible!
*
* We read source bytes into get_buffer and dole out bits as needed.
* If get_buffer already contains enough bits, they are fetched in-line
* by the macros check_bit_buffer and get_bits. When there aren't enough
* bits, fill_bit_buffer is called; it will attempt to fill get_buffer to
* the "high water mark" (not just to the number of bits needed; this reduces
* the function-call overhead cost of entering fill_bit_buffer).
* On return, fill_bit_buffer guarantees that get_buffer contains at least
* the requested number of bits --- dummy zeroes are inserted if necessary.
*
* On most machines MIN_GET_BITS should be 25 to allow the full 32-bit width
* of get_buffer to be used. (On machines with wider words, an even larger
* buffer could be used.) However, on some machines 32-bit shifts are
* relatively slow and take time proportional to the number of places shifted.
* (This is true with most PC compilers, for instance.) In this case it may
* be a win to set MIN_GET_BITS to the minimum value of 15. This reduces the
* average shift distance at the cost of more calls to fill_bit_buffer.
*/
#ifdef SLOW_SHIFT_32
#define MIN_GET_BITS 15 /* minimum allowable value */
#else
#define MIN_GET_BITS 25 /* max value for 32-bit get_buffer */
#endif
LOCAL void
fill_bit_buffer (int nbits)
/* Load up the bit buffer to a depth of at least nbits */
{
/* Attempt to load at least MIN_GET_BITS bits into get_buffer. */
/* (It is assumed that no request will be for more than that many bits.) */
while (bits_left < MIN_GET_BITS) {
register int c = JGETC(dcinfo);
/* If it's 0xFF, check and discard stuffed zero byte */
if (c == 0xFF) {
int c2 = JGETC(dcinfo);
if (c2 != 0) {
/* Oops, it's actually a marker indicating end of compressed data. */
/* Better put it back for use later */
JUNGETC(c2,dcinfo);
JUNGETC(c,dcinfo);
/* There should be enough bits still left in the data segment; */
/* if so, just break out of the while loop. */
if (bits_left >= nbits)
break;
/* Uh-oh. Report corrupted data to user and stuff zeroes into
* the data stream, so that we can produce some kind of image.
* Note that this will be repeated for each byte demanded for the
* rest of the segment; this is a bit slow but not unreasonably so.
* The main thing is to avoid getting a zillion warnings, hence
* we use a flag to ensure that only one warning appears.
*/
if (! printed_eod) {
WARNMS(dcinfo->emethods, "Corrupt JPEG data: premature end of data segment");
printed_eod = TRUE;
}
c = 0; /* insert a zero byte into bit buffer */
}
}
/* OK, load c into get_buffer */
get_buffer = (get_buffer << 8) | c;
bits_left += 8;
}
}
/*
* These macros provide the in-line portion of bit fetching.
* Correct usage is:
* check_bit_buffer(n); ensure there are N bits in get_buffer
* val = get_bits(n); fetch N bits
* The value n should be a simple variable, not an expression, because it
* is evaluated multiple times.
* peek_bits() fetches next N bits without removing them from the buffer.
*/
#define check_bit_buffer(nbits) \
{ if (bits_left < (nbits)) fill_bit_buffer(nbits); }
#define get_bits(nbits) \
(((int) (get_buffer >> (bits_left -= (nbits)))) & ((1<<(nbits))-1))
#define peek_bits(nbits) \
(((int) (get_buffer >> (bits_left - (nbits)))) & ((1<<(nbits))-1))
/*
* Routines to extract next Huffman-coded symbol from input bit stream.
* We use a lookahead table to process codes of up to HUFF_LOOKAHEAD bits
* without looping. Usually, more than 95% of the Huffman codes will be 8
* or fewer bits long. The few overlength codes are handled with a loop.
* The primary case is made a macro for speed reasons; the secondary
* routine slow_DECODE is rarely entered and need not be inline code.
*
* Notes about the huff_DECODE macro:
* 1. The first if-test is coded to call fill_bit_buffer only when necessary.
* 2. If the lookahead succeeds, we need only decrement bits_left to remove
* the proper number of bits from get_buffer.
* 3. If the lookahead table contains no entry, the next code must be
* more than HUFF_LOOKAHEAD bits long.
* 4. Near the end of the data segment, we may fail to get enough bits
* for a lookahead. In that case, we do it the hard way.
*/
#define huff_DECODE(htbl,result) \
{ register int nb, look; \
if (bits_left >= HUFF_LOOKAHEAD || \
(fill_bit_buffer(0), bits_left >= HUFF_LOOKAHEAD)) { \
look = peek_bits(HUFF_LOOKAHEAD); \
if ((nb = htbl->priv.dec.look_nbits[look]) != 0) { \
bits_left -= nb; \
result = htbl->priv.dec.look_sym[look]; \
} else \
result = slow_DECODE(htbl, HUFF_LOOKAHEAD+1); \
} else \
result = slow_DECODE(htbl, 1); \
}
LOCAL int
slow_DECODE (HUFF_TBL * htbl, int min_bits)
{
register int l = min_bits;
register INT32 code;
/* huff_DECODE has determined that the code is at least min_bits */
/* bits long, so fetch that many bits in one swoop. */
check_bit_buffer(l);
code = get_bits(l);
/* Collect the rest of the Huffman code one bit at a time. */
/* This is per Figure F.16 in the JPEG spec. */
while (code > htbl->priv.dec.maxcode[l]) {
code <<= 1;
check_bit_buffer(1);
code |= get_bits(1);
l++;
}
/* With garbage input we may reach the sentinel value l = 17. */
if (l > 16) {
WARNMS(dcinfo->emethods, "Corrupt JPEG data: bad Huffman code");
return 0; /* fake a zero as the safest result */
}
return htbl->huffval[ htbl->priv.dec.valptr[l] +
((int) (code - htbl->priv.dec.mincode[l])) ];
}
/* Figure F.12: extend sign bit.
* On some machines, a shift and add will be faster than a table lookup.
*/
#ifdef AVOID_TABLES
#define huff_EXTEND(x,s) ((x) < (1<<((s)-1)) ? (x) + (((-1)<<(s)) + 1) : (x))
#else
#define huff_EXTEND(x,s) ((x) < extend_test[s] ? (x) + extend_offset[s] : (x))
static const int extend_test[16] = /* entry n is 2**(n-1) */
{ 0, 0x0001, 0x0002, 0x0004, 0x0008, 0x0010, 0x0020, 0x0040, 0x0080,
0x0100, 0x0200, 0x0400, 0x0800, 0x1000, 0x2000, 0x4000 };
static const int extend_offset[16] = /* entry n is (-1 << n) + 1 */
{ 0, ((-1)<<1) + 1, ((-1)<<2) + 1, ((-1)<<3) + 1, ((-1)<<4) + 1,
((-1)<<5) + 1, ((-1)<<6) + 1, ((-1)<<7) + 1, ((-1)<<8) + 1,
((-1)<<9) + 1, ((-1)<<10) + 1, ((-1)<<11) + 1, ((-1)<<12) + 1,
((-1)<<13) + 1, ((-1)<<14) + 1, ((-1)<<15) + 1 };
#endif /* AVOID_TABLES */
/*
* Initialize for a Huffman-compressed scan.
* This is invoked after reading the SOS marker.
*/
METHODDEF void
decoder_init (decompress_info_ptr cinfo)
{
short ci;
jpeg_component_info * compptr;
/* Initialize static variables */
dcinfo = cinfo;
bits_left = 0;
printed_eod = FALSE;
for (ci = 0; ci < cinfo->comps_in_scan; ci++) {
compptr = cinfo->cur_comp_info[ci];
/* Make sure requested tables are present */
if (cinfo->dc_huff_tbl_ptrs[compptr->dc_tbl_no] == NULL ||
cinfo->ac_huff_tbl_ptrs[compptr->ac_tbl_no] == NULL)
ERREXIT(cinfo->emethods, "Use of undefined Huffman table");
/* Compute derived values for Huffman tables */
/* We may do this more than once for same table, but it's not a big deal */
fix_huff_tbl(cinfo->dc_huff_tbl_ptrs[compptr->dc_tbl_no]);
fix_huff_tbl(cinfo->ac_huff_tbl_ptrs[compptr->ac_tbl_no]);
/* Initialize DC predictions to 0 */
cinfo->last_dc_val[ci] = 0;
}
/* Initialize restart stuff */
cinfo->restarts_to_go = cinfo->restart_interval;
cinfo->next_restart_num = 0;
}
/*
* Check for a restart marker & resynchronize decoder.
*/
LOCAL void
process_restart (decompress_info_ptr cinfo)
{
int c, nbytes;
short ci;
/* Throw away any unused bits remaining in bit buffer */
nbytes = bits_left / 8; /* count any full bytes loaded into buffer */
bits_left = 0;
printed_eod = FALSE; /* next segment can get another warning */
/* Scan for next JPEG marker */
do {
do { /* skip any non-FF bytes */
nbytes++;
c = JGETC(cinfo);
} while (c != 0xFF);
do { /* skip any duplicate FFs */
/* we don't increment nbytes here since extra FFs are legal */
c = JGETC(cinfo);
} while (c == 0xFF);
} while (c == 0); /* repeat if it was a stuffed FF/00 */
if (nbytes != 1)
WARNMS2(cinfo->emethods,
"Corrupt JPEG data: %d extraneous bytes before marker 0x%02x",
nbytes-1, c);
if (c != (RST0 + cinfo->next_restart_num)) {
/* Uh-oh, the restart markers have been messed up too. */
/* Let the file-format module try to figure out how to resync. */
(*cinfo->methods->resync_to_restart) (cinfo, c);
} else
TRACEMS1(cinfo->emethods, 2, "RST%d", cinfo->next_restart_num);
/* Re-initialize DC predictions to 0 */
for (ci = 0; ci < cinfo->comps_in_scan; ci++)
cinfo->last_dc_val[ci] = 0;
/* Update restart state */
cinfo->restarts_to_go = cinfo->restart_interval;
cinfo->next_restart_num = (cinfo->next_restart_num + 1) & 7;
}
/* ZAG[i] is the natural-order position of the i'th element of zigzag order.
* If the incoming data is corrupted, decode_mcu could attempt to
* reference values beyond the end of the array. To avoid a wild store,
* we put some extra zeroes after the real entries.
*/
static const short ZAG[DCTSIZE2+16] = {
0, 1, 8, 16, 9, 2, 3, 10,
17, 24, 32, 25, 18, 11, 4, 5,
12, 19, 26, 33, 40, 48, 41, 34,
27, 20, 13, 6, 7, 14, 21, 28,
35, 42, 49, 56, 57, 50, 43, 36,
29, 22, 15, 23, 30, 37, 44, 51,
58, 59, 52, 45, 38, 31, 39, 46,
53, 60, 61, 54, 47, 55, 62, 63,
0, 0, 0, 0, 0, 0, 0, 0, /* extra entries in case k>63 below */
0, 0, 0, 0, 0, 0, 0, 0
};
/*
* Decode and return one MCU's worth of Huffman-compressed coefficients.
* This routine also handles quantization descaling and zigzag reordering
* of coefficient values.
*
* The i'th block of the MCU is stored into the block pointed to by
* MCU_data[i]. WE ASSUME THIS AREA HAS BEEN ZEROED BY THE CALLER.
* (Wholesale zeroing is usually a little faster than retail...)
*/
METHODDEF void
decode_mcu (decompress_info_ptr cinfo, JBLOCKROW *MCU_data)
{
register int s, k, r;
short blkn, ci;
register JBLOCKROW block;
register QUANT_TBL_PTR quanttbl;
HUFF_TBL *dctbl;
HUFF_TBL *actbl;
jpeg_component_info * compptr;
/* Account for restart interval, process restart marker if needed */
if (cinfo->restart_interval) {
if (cinfo->restarts_to_go == 0)
process_restart(cinfo);
cinfo->restarts_to_go--;
}
/* Outer loop handles each block in the MCU */
for (blkn = 0; blkn < cinfo->blocks_in_MCU; blkn++) {
block = MCU_data[blkn];
ci = cinfo->MCU_membership[blkn];
compptr = cinfo->cur_comp_info[ci];
quanttbl = cinfo->quant_tbl_ptrs[compptr->quant_tbl_no];
actbl = cinfo->ac_huff_tbl_ptrs[compptr->ac_tbl_no];
dctbl = cinfo->dc_huff_tbl_ptrs[compptr->dc_tbl_no];
/* Decode a single block's worth of coefficients */
/* Section F.2.2.1: decode the DC coefficient difference */
huff_DECODE(dctbl, s);
if (s) {
check_bit_buffer(s);
r = get_bits(s);
s = huff_EXTEND(r, s);
}
/* Convert DC difference to actual value, update last_dc_val */
s += cinfo->last_dc_val[ci];
cinfo->last_dc_val[ci] = (JCOEF) s;
/* Descale and output the DC coefficient (assumes ZAG[0] = 0) */
(*block)[0] = (JCOEF) (((JCOEF) s) * quanttbl[0]);
/* Section F.2.2.2: decode the AC coefficients */
/* Since zero values are skipped, output area must be zeroed beforehand */
for (k = 1; k < DCTSIZE2; k++) {
huff_DECODE(actbl, s);
r = s >> 4;
s &= 15;
if (s) {
k += r;
check_bit_buffer(s);
r = get_bits(s);
s = huff_EXTEND(r, s);
/* Descale coefficient and output in natural (dezigzagged) order */
(*block)[ZAG[k]] = (JCOEF) (((JCOEF) s) * quanttbl[k]);
} else {
if (r != 15)
break;
k += 15;
}
}
}
}
/*
* Finish up at the end of a Huffman-compressed scan.
*/
METHODDEF void
decoder_term (decompress_info_ptr cinfo)
{
/* No work needed */
}
/*
* The method selection routine for Huffman entropy decoding.
*/
GLOBAL void
jseldhuffman (decompress_info_ptr cinfo)
{
if (! cinfo->arith_code) {
cinfo->methods->entropy_decode_init = decoder_init;
cinfo->methods->entropy_decode = decode_mcu;
cinfo->methods->entropy_decode_term = decoder_term;
}
}
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