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/*
* jdhuff.c
*
* Copyright (C) 1991-1994, 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.
*
* Much of the complexity here has to do with supporting input suspension.
* If the data source module demands suspension, we want to be able to back
* up to the start of the current MCU. To do this, we copy state variables
* into local working storage, and update them back to the permanent JPEG
* objects only upon successful completion of an MCU.
*/
#define JPEG_INTERNALS
#include "jinclude.h"
#include "jpeglib.h"
/* Derived data constructed for each Huffman table */
#define HUFF_LOOKAHEAD 8 /* # of bits of lookahead */
typedef struct {
/* Basic tables: (element [0] of each array is unused) */
INT32 mincode[17]; /* smallest code of length k */
INT32 maxcode[18]; /* largest code of length k (-1 if none) */
/* (maxcode[17] is a sentinel to ensure huff_DECODE terminates) */
int valptr[17]; /* huffval[] index of 1st symbol of length k */
/* Back link to public Huffman table (needed only in slow_DECODE) */
JHUFF_TBL *pub;
/* Lookahead tables: indexed by the next HUFF_LOOKAHEAD bits of
* the input data stream. If the next Huffman code is no more
* than HUFF_LOOKAHEAD bits long, we can obtain its length and
* the corresponding symbol directly from these tables.
*/
int look_nbits[1<<HUFF_LOOKAHEAD]; /* # bits, or 0 if too long */
UINT8 look_sym[1<<HUFF_LOOKAHEAD]; /* symbol, or unused */
} D_DERIVED_TBL;
/* Expanded entropy decoder object for Huffman decoding.
*
* The savable_state subrecord contains fields that change within an MCU,
* but must not be updated permanently until we complete the MCU.
*/
typedef struct {
INT32 get_buffer; /* current bit-extraction buffer */
int bits_left; /* # of unused bits in it */
int last_dc_val[MAX_COMPS_IN_SCAN]; /* last DC coef for each component */
} savable_state;
/* This macro is to work around compilers with missing or broken
* structure assignment. You'll need to fix this code if you have
* such a compiler and you change MAX_COMPS_IN_SCAN.
*/
#ifndef NO_STRUCT_ASSIGN
#define ASSIGN_STATE(dest,src) ((dest) = (src))
#else
#if MAX_COMPS_IN_SCAN == 4
#define ASSIGN_STATE(dest,src) \
((dest).get_buffer = (src).get_buffer, \
(dest).bits_left = (src).bits_left, \
(dest).last_dc_val[0] = (src).last_dc_val[0], \
(dest).last_dc_val[1] = (src).last_dc_val[1], \
(dest).last_dc_val[2] = (src).last_dc_val[2], \
(dest).last_dc_val[3] = (src).last_dc_val[3])
#endif
#endif
typedef struct {
struct jpeg_entropy_decoder pub; /* public fields */
savable_state saved; /* Bit buffer & DC state at start of MCU */
/* These fields are NOT loaded into local working state. */
unsigned int restarts_to_go; /* MCUs left in this restart interval */
boolean printed_eod; /* flag to suppress extra end-of-data msgs */
/* Pointers to derived tables (these workspaces have image lifespan) */
D_DERIVED_TBL * dc_derived_tbls[NUM_HUFF_TBLS];
D_DERIVED_TBL * ac_derived_tbls[NUM_HUFF_TBLS];
} huff_entropy_decoder;
typedef huff_entropy_decoder * huff_entropy_ptr;
/* Working state while scanning an MCU.
* This struct contains all the fields that are needed by subroutines.
*/
typedef struct {
int unread_marker; /* nonzero if we have hit a marker */
const JOCTET * next_input_byte; /* => next byte to read from source */
size_t bytes_in_buffer; /* # of bytes remaining in source buffer */
savable_state cur; /* Current bit buffer & DC state */
j_decompress_ptr cinfo; /* fill_bit_buffer needs access to this */
} working_state;
/* Forward declarations */
LOCAL void fix_huff_tbl JPP((j_decompress_ptr cinfo, JHUFF_TBL * htbl,
D_DERIVED_TBL ** pdtbl));
/*
* Initialize for a Huffman-compressed scan.
*/
METHODDEF void
start_pass_huff_decoder (j_decompress_ptr cinfo)
{
huff_entropy_ptr entropy = (huff_entropy_ptr) cinfo->entropy;
int ci, dctbl, actbl;
jpeg_component_info * compptr;
for (ci = 0; ci < cinfo->comps_in_scan; ci++) {
compptr = cinfo->cur_comp_info[ci];
dctbl = compptr->dc_tbl_no;
actbl = compptr->ac_tbl_no;
/* Make sure requested tables are present */
if (dctbl < 0 || dctbl >= NUM_HUFF_TBLS ||
cinfo->dc_huff_tbl_ptrs[dctbl] == NULL)
ERREXIT1(cinfo, JERR_NO_HUFF_TABLE, dctbl);
if (actbl < 0 || actbl >= NUM_HUFF_TBLS ||
cinfo->ac_huff_tbl_ptrs[actbl] == NULL)
ERREXIT1(cinfo, JERR_NO_HUFF_TABLE, actbl);
/* Compute derived values for Huffman tables */
/* We may do this more than once for a table, but it's not expensive */
fix_huff_tbl(cinfo, cinfo->dc_huff_tbl_ptrs[dctbl],
& entropy->dc_derived_tbls[dctbl]);
fix_huff_tbl(cinfo, cinfo->ac_huff_tbl_ptrs[actbl],
& entropy->ac_derived_tbls[actbl]);
/* Initialize DC predictions to 0 */
entropy->saved.last_dc_val[ci] = 0;
}
/* Initialize private state variables */
entropy->saved.bits_left = 0;
entropy->saved.get_buffer = 0; /* unnecessary, but keeps Purify quiet */
entropy->printed_eod = FALSE;
/* Initialize restart counter */
entropy->restarts_to_go = cinfo->restart_interval;
}
LOCAL void
fix_huff_tbl (j_decompress_ptr cinfo, JHUFF_TBL * htbl, D_DERIVED_TBL ** pdtbl)
/* Compute the derived values for a Huffman table */
{
D_DERIVED_TBL *dtbl;
int p, i, l, si;
int lookbits, ctr;
char huffsize[257];
unsigned int huffcode[257];
unsigned int code;
/* Allocate a workspace if we haven't already done so. */
if (*pdtbl == NULL)
*pdtbl = (D_DERIVED_TBL *)
(*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE,
SIZEOF(D_DERIVED_TBL));
dtbl = *pdtbl;
dtbl->pub = htbl; /* fill in back link */
/* 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]) {
dtbl->valptr[l] = p; /* huffval[] index of 1st symbol of code length l */
dtbl->mincode[l] = huffcode[p]; /* minimum code of length l */
p += htbl->bits[l];
dtbl->maxcode[l] = huffcode[p-1]; /* maximum code of length l */
} else {
dtbl->maxcode[l] = -1; /* -1 if no codes of this length */
}
}
dtbl->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(dtbl->look_nbits, SIZEOF(dtbl->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--) {
dtbl->look_nbits[lookbits] = l;
dtbl->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).
* Note that fill_bit_buffer may return FALSE to indicate suspension.
* On TRUE 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
* quite 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 boolean
fill_bit_buffer (working_state * state, int nbits)
/* Load up the bit buffer to a depth of at least nbits */
{
/* Copy heavily used state fields into locals (hopefully registers) */
register const JOCTET * next_input_byte = state->next_input_byte;
register size_t bytes_in_buffer = state->bytes_in_buffer;
register INT32 get_buffer = state->cur.get_buffer;
register int bits_left = state->cur.bits_left;
register int c;
/* 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) {
/* Attempt to read a byte */
if (state->unread_marker != 0)
goto no_more_data; /* can't advance past a marker */
if (bytes_in_buffer == 0) {
if (! (*state->cinfo->src->fill_input_buffer) (state->cinfo))
return FALSE;
next_input_byte = state->cinfo->src->next_input_byte;
bytes_in_buffer = state->cinfo->src->bytes_in_buffer;
}
bytes_in_buffer--;
c = GETJOCTET(*next_input_byte++);
/* If it's 0xFF, check and discard stuffed zero byte */
if (c == 0xFF) {
do {
if (bytes_in_buffer == 0) {
if (! (*state->cinfo->src->fill_input_buffer) (state->cinfo))
return FALSE;
next_input_byte = state->cinfo->src->next_input_byte;
bytes_in_buffer = state->cinfo->src->bytes_in_buffer;
}
bytes_in_buffer--;
c = GETJOCTET(*next_input_byte++);
} while (c == 0xFF);
if (c == 0) {
/* Found FF/00, which represents an FF data byte */
c = 0xFF;
} else {
/* Oops, it's actually a marker indicating end of compressed data. */
/* Better put it back for use later */
state->unread_marker = c;
no_more_data:
/* There should be enough bits still left in the data segment; */
/* if so, just break out of the outer 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 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 (! ((huff_entropy_ptr) state->cinfo->entropy)->printed_eod) {
WARNMS(state->cinfo, JWRN_HIT_MARKER);
((huff_entropy_ptr) state->cinfo->entropy)->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;
}
/* Unload the local registers */
state->next_input_byte = next_input_byte;
state->bytes_in_buffer = bytes_in_buffer;
state->cur.get_buffer = get_buffer;
state->cur.bits_left = bits_left;
return TRUE;
}
/*
* These macros provide the in-line portion of bit fetching.
* Use check_bit_buffer to ensure there are N bits in get_buffer
* before using get_bits, peek_bits, or drop_bits.
* check_bit_buffer(state,n,action);
* Ensure there are N bits in get_buffer; if suspend, take action.
* val = get_bits(state,n);
* Fetch next N bits.
* val = peek_bits(state,n);
* Fetch next N bits without removing them from the buffer.
* drop_bits(state,n);
* Discard next N bits.
* The value N should be a simple variable, not an expression, because it
* is evaluated multiple times.
*/
#define check_bit_buffer(state,nbits,action) \
{ if ((state).cur.bits_left < (nbits)) \
if (! fill_bit_buffer(&(state), nbits)) \
{ action; } }
#define get_bits(state,nbits) \
(((int) ((state).cur.get_buffer >> ((state).cur.bits_left -= (nbits)))) & ((1<<(nbits))-1))
#define peek_bits(state,nbits) \
(((int) ((state).cur.get_buffer >> ((state).cur.bits_left - (nbits)))) & ((1<<(nbits))-1))
#define drop_bits(state,nbits) \
((state).cur.bits_left -= (nbits))
/*
* Code for extracting 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. 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.
* 2. If the lookahead table contains no entry, the next code must be
* more than HUFF_LOOKAHEAD bits long.
* 3. slow_DECODE returns -1 if forced to suspend.
*/
#define huff_DECODE(result,state,htbl,donelabel) \
{ if (state.cur.bits_left < HUFF_LOOKAHEAD) { \
if (! fill_bit_buffer(&state, 0)) return FALSE; \
if (state.cur.bits_left < HUFF_LOOKAHEAD) { \
if ((result = slow_DECODE(&state, htbl, 1)) < 0) return FALSE; \
goto donelabel; \
} \
} \
{ register int nb, look; \
look = peek_bits(state, HUFF_LOOKAHEAD); \
if ((nb = htbl->look_nbits[look]) != 0) { \
drop_bits(state, nb); \
result = htbl->look_sym[look]; \
} else { \
if ((result = slow_DECODE(&state, htbl, HUFF_LOOKAHEAD+1)) < 0) \
return FALSE; \
} \
} \
donelabel:; \
}
LOCAL int
slow_DECODE (working_state * state, D_DERIVED_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(*state, l, return -1);
code = get_bits(*state, 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->maxcode[l]) {
code <<= 1;
check_bit_buffer(*state, 1, return -1);
code |= get_bits(*state, 1);
l++;
}
/* With garbage input we may reach the sentinel value l = 17. */
if (l > 16) {
WARNMS(state->cinfo, JWRN_HUFF_BAD_CODE);
return 0; /* fake a zero as the safest result */
}
return htbl->pub->huffval[ htbl->valptr[l] +
((int) (code - htbl->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 */
/*
* Check for a restart marker & resynchronize decoder.
* Returns FALSE if must suspend.
*/
LOCAL boolean
process_restart (j_decompress_ptr cinfo)
{
huff_entropy_ptr entropy = (huff_entropy_ptr) cinfo->entropy;
int ci;
/* Throw away any unused bits remaining in bit buffer; */
/* include any full bytes in next_marker's count of discarded bytes */
cinfo->marker->discarded_bytes += entropy->saved.bits_left / 8;
entropy->saved.bits_left = 0;
/* Advance past the RSTn marker */
if (! (*cinfo->marker->read_restart_marker) (cinfo))
return FALSE;
/* Re-initialize DC predictions to 0 */
for (ci = 0; ci < cinfo->comps_in_scan; ci++)
entropy->saved.last_dc_val[ci] = 0;
/* Reset restart counter */
entropy->restarts_to_go = cinfo->restart_interval;
entropy->printed_eod = FALSE; /* next segment can get another warning */
return TRUE;
}
/* 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 int 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.
* The coefficients are reordered from zigzag order into natural array order,
* but are not dequantized.
*
* 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...)
*
* Returns FALSE if data source requested suspension. In that case no
* changes have been made to permanent state. (Exception: some output
* coefficients may already have been assigned. This is harmless for
* this module, but would not work for decoding progressive JPEG.)
*/
METHODDEF boolean
decode_mcu (j_decompress_ptr cinfo, JBLOCKROW *MCU_data)
{
huff_entropy_ptr entropy = (huff_entropy_ptr) cinfo->entropy;
register int s, k, r;
int blkn, ci;
JBLOCKROW block;
working_state state;
D_DERIVED_TBL * dctbl;
D_DERIVED_TBL * actbl;
jpeg_component_info * compptr;
/* Process restart marker if needed; may have to suspend */
if (cinfo->restart_interval) {
if (entropy->restarts_to_go == 0)
if (! process_restart(cinfo))
return FALSE;
}
/* Load up working state */
state.unread_marker = cinfo->unread_marker;
state.next_input_byte = cinfo->src->next_input_byte;
state.bytes_in_buffer = cinfo->src->bytes_in_buffer;
ASSIGN_STATE(state.cur, entropy->saved);
state.cinfo = cinfo;
/* 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];
dctbl = entropy->dc_derived_tbls[compptr->dc_tbl_no];
actbl = entropy->ac_derived_tbls[compptr->ac_tbl_no];
/* Decode a single block's worth of coefficients */
/* Section F.2.2.1: decode the DC coefficient difference */
huff_DECODE(s, state, dctbl, label1);
if (s) {
check_bit_buffer(state, s, return FALSE);
r = get_bits(state, s);
s = huff_EXTEND(r, s);
}
/* Shortcut if component's values are not interesting */
if (! compptr->component_needed)
goto skip_ACs;
/* Convert DC difference to actual value, update last_dc_val */
s += state.cur.last_dc_val[ci];
state.cur.last_dc_val[ci] = s;
/* Output the DC coefficient (assumes ZAG[0] = 0) */
(*block)[0] = (JCOEF) s;
/* Do we need to decode the AC coefficients for this component? */
if (compptr->DCT_scaled_size > 1) {
/* Section F.2.2.2: decode the AC coefficients */
/* Since zeroes are skipped, output area must be cleared beforehand */
for (k = 1; k < DCTSIZE2; k++) {
huff_DECODE(s, state, actbl, label2);
r = s >> 4;
s &= 15;
if (s) {
k += r;
check_bit_buffer(state, s, return FALSE);
r = get_bits(state, s);
s = huff_EXTEND(r, s);
/* Output coefficient in natural (dezigzagged) order */
(*block)[ZAG[k]] = (JCOEF) s;
} else {
if (r != 15)
break;
k += 15;
}
}
} else {
skip_ACs:
/* Section F.2.2.2: decode the AC coefficients */
/* In this path we just discard the values */
for (k = 1; k < DCTSIZE2; k++) {
huff_DECODE(s, state, actbl, label3);
r = s >> 4;
s &= 15;
if (s) {
k += r;
check_bit_buffer(state, s, return FALSE);
drop_bits(state, s);
} else {
if (r != 15)
break;
k += 15;
}
}
}
}
/* Completed MCU, so update state */
cinfo->unread_marker = state.unread_marker;
cinfo->src->next_input_byte = state.next_input_byte;
cinfo->src->bytes_in_buffer = state.bytes_in_buffer;
ASSIGN_STATE(entropy->saved, state.cur);
/* Account for restart interval (no-op if not using restarts) */
entropy->restarts_to_go--;
return TRUE;
}
/*
* Module initialization routine for Huffman entropy decoding.
*/
GLOBAL void
jinit_huff_decoder (j_decompress_ptr cinfo)
{
huff_entropy_ptr entropy;
int i;
entropy = (huff_entropy_ptr)
(*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE,
SIZEOF(huff_entropy_decoder));
cinfo->entropy = (struct jpeg_entropy_decoder *) entropy;
entropy->pub.start_pass = start_pass_huff_decoder;
entropy->pub.decode_mcu = decode_mcu;
/* Mark tables unallocated */
for (i = 0; i < NUM_HUFF_TBLS; i++) {
entropy->dc_derived_tbls[i] = entropy->ac_derived_tbls[i] = NULL;
}
}
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