ref: 7ab86494986671bf38464435f57fb6f925ce8632
dir: /sys/src/cmd/gs/jpeg/jdhuff.c/
/*
* jdhuff.c
*
* Copyright (C) 1991-1997, 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
* storage only upon successful completion of an MCU.
*/
#define JPEG_INTERNALS
#include "jinclude.h"
#include "jpeglib.h"
#include "jdhuff.h" /* Declarations shared with jdphuff.c */
/*
* 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 {
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).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 */
/* These fields are loaded into local variables at start of each MCU.
* In case of suspension, we exit WITHOUT updating them.
*/
bitread_perm_state bitstate; /* Bit buffer at start of MCU */
savable_state saved; /* Other 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 */
/* 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];
/* Precalculated info set up by start_pass for use in decode_mcu: */
/* Pointers to derived tables to be used for each block within an MCU */
d_derived_tbl * dc_cur_tbls[D_MAX_BLOCKS_IN_MCU];
d_derived_tbl * ac_cur_tbls[D_MAX_BLOCKS_IN_MCU];
/* Whether we care about the DC and AC coefficient values for each block */
boolean dc_needed[D_MAX_BLOCKS_IN_MCU];
boolean ac_needed[D_MAX_BLOCKS_IN_MCU];
} huff_entropy_decoder;
typedef huff_entropy_decoder * huff_entropy_ptr;
/*
* 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, blkn, dctbl, actbl;
jpeg_component_info * compptr;
/* Check that the scan parameters Ss, Se, Ah/Al are OK for sequential JPEG.
* This ought to be an error condition, but we make it a warning because
* there are some baseline files out there with all zeroes in these bytes.
*/
if (cinfo->Ss != 0 || cinfo->Se != DCTSIZE2-1 ||
cinfo->Ah != 0 || cinfo->Al != 0)
WARNMS(cinfo, JWRN_NOT_SEQUENTIAL);
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;
/* Compute derived values for Huffman tables */
/* We may do this more than once for a table, but it's not expensive */
jpeg_make_d_derived_tbl(cinfo, TRUE, dctbl,
& entropy->dc_derived_tbls[dctbl]);
jpeg_make_d_derived_tbl(cinfo, FALSE, actbl,
& entropy->ac_derived_tbls[actbl]);
/* Initialize DC predictions to 0 */
entropy->saved.last_dc_val[ci] = 0;
}
/* Precalculate decoding info for each block in an MCU of this scan */
for (blkn = 0; blkn < cinfo->blocks_in_MCU; blkn++) {
ci = cinfo->MCU_membership[blkn];
compptr = cinfo->cur_comp_info[ci];
/* Precalculate which table to use for each block */
entropy->dc_cur_tbls[blkn] = entropy->dc_derived_tbls[compptr->dc_tbl_no];
entropy->ac_cur_tbls[blkn] = entropy->ac_derived_tbls[compptr->ac_tbl_no];
/* Decide whether we really care about the coefficient values */
if (compptr->component_needed) {
entropy->dc_needed[blkn] = TRUE;
/* we don't need the ACs if producing a 1/8th-size image */
entropy->ac_needed[blkn] = (compptr->DCT_scaled_size > 1);
} else {
entropy->dc_needed[blkn] = entropy->ac_needed[blkn] = FALSE;
}
}
/* Initialize bitread state variables */
entropy->bitstate.bits_left = 0;
entropy->bitstate.get_buffer = 0; /* unnecessary, but keeps Purify quiet */
entropy->pub.insufficient_data = FALSE;
/* Initialize restart counter */
entropy->restarts_to_go = cinfo->restart_interval;
}
/*
* Compute the derived values for a Huffman table.
* This routine also performs some validation checks on the table.
*
* Note this is also used by jdphuff.c.
*/
GLOBAL(void)
jpeg_make_d_derived_tbl (j_decompress_ptr cinfo, boolean isDC, int tblno,
d_derived_tbl ** pdtbl)
{
JHUFF_TBL *htbl;
d_derived_tbl *dtbl;
int p, i, l, si, numsymbols;
int lookbits, ctr;
char huffsize[257];
unsigned int huffcode[257];
unsigned int code;
/* Note that huffsize[] and huffcode[] are filled in code-length order,
* paralleling the order of the symbols themselves in htbl->huffval[].
*/
/* Find the input Huffman table */
if (tblno < 0 || tblno >= NUM_HUFF_TBLS)
ERREXIT1(cinfo, JERR_NO_HUFF_TABLE, tblno);
htbl =
isDC ? cinfo->dc_huff_tbl_ptrs[tblno] : cinfo->ac_huff_tbl_ptrs[tblno];
if (htbl == NULL)
ERREXIT1(cinfo, JERR_NO_HUFF_TABLE, tblno);
/* 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 */
p = 0;
for (l = 1; l <= 16; l++) {
i = (int) htbl->bits[l];
if (i < 0 || p + i > 256) /* protect against table overrun */
ERREXIT(cinfo, JERR_BAD_HUFF_TABLE);
while (i--)
huffsize[p++] = (char) l;
}
huffsize[p] = 0;
numsymbols = p;
/* Figure C.2: generate the codes themselves */
/* We also validate that the counts represent a legal Huffman code tree. */
code = 0;
si = huffsize[0];
p = 0;
while (huffsize[p]) {
while (((int) huffsize[p]) == si) {
huffcode[p++] = code;
code++;
}
/* code is now 1 more than the last code used for codelength si; but
* it must still fit in si bits, since no code is allowed to be all ones.
*/
if (((INT32) code) >= (((INT32) 1) << si))
ERREXIT(cinfo, JERR_BAD_HUFF_TABLE);
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]) {
/* valoffset[l] = huffval[] index of 1st symbol of code length l,
* minus the minimum code of length l
*/
dtbl->valoffset[l] = (INT32) p - (INT32) huffcode[p];
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 jpeg_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++;
}
}
}
/* Validate symbols as being reasonable.
* For AC tables, we make no check, but accept all byte values 0..255.
* For DC tables, we require the symbols to be in range 0..15.
* (Tighter bounds could be applied depending on the data depth and mode,
* but this is sufficient to ensure safe decoding.)
*/
if (isDC) {
for (i = 0; i < numsymbols; i++) {
int sym = htbl->huffval[i];
if (sym < 0 || sym > 15)
ERREXIT(cinfo, JERR_BAD_HUFF_TABLE);
}
}
}
/*
* Out-of-line code for bit fetching (shared with jdphuff.c).
* See jdhuff.h for info about usage.
* Note: current values of get_buffer and bits_left are passed as parameters,
* but are returned in the corresponding fields of the state struct.
*
* 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 jpeg_fill_bit_buffer.
*/
#ifdef SLOW_SHIFT_32
#define MIN_GET_BITS 15 /* minimum allowable value */
#else
#define MIN_GET_BITS (BIT_BUF_SIZE-7)
#endif
GLOBAL(boolean)
jpeg_fill_bit_buffer (bitread_working_state * state,
register bit_buf_type get_buffer, register int bits_left,
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;
j_decompress_ptr cinfo = state->cinfo;
/* 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.) */
/* We fail to do so only if we hit a marker or are forced to suspend. */
if (cinfo->unread_marker == 0) { /* cannot advance past a marker */
while (bits_left < MIN_GET_BITS) {
register int c;
/* Attempt to read a byte */
if (bytes_in_buffer == 0) {
if (! (*cinfo->src->fill_input_buffer) (cinfo))
return FALSE;
next_input_byte = cinfo->src->next_input_byte;
bytes_in_buffer = 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) {
/* Loop here to discard any padding FF's on terminating marker,
* so that we can save a valid unread_marker value. NOTE: we will
* accept multiple FF's followed by a 0 as meaning a single FF data
* byte. This data pattern is not valid according to the standard.
*/
do {
if (bytes_in_buffer == 0) {
if (! (*cinfo->src->fill_input_buffer) (cinfo))
return FALSE;
next_input_byte = cinfo->src->next_input_byte;
bytes_in_buffer = 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.
* Save the marker code for later use.
* Fine point: it might appear that we should save the marker into
* bitread working state, not straight into permanent state. But
* once we have hit a marker, we cannot need to suspend within the
* current MCU, because we will read no more bytes from the data
* source. So it is OK to update permanent state right away.
*/
cinfo->unread_marker = c;
/* See if we need to insert some fake zero bits. */
goto no_more_bytes;
}
}
/* OK, load c into get_buffer */
get_buffer = (get_buffer << 8) | c;
bits_left += 8;
} /* end while */
} else {
no_more_bytes:
/* We get here if we've read the marker that terminates the compressed
* data segment. There should be enough bits in the buffer register
* to satisfy the request; if so, no problem.
*/
if (nbits > bits_left) {
/* Uh-oh. Report corrupted data to user and stuff zeroes into
* the data stream, so that we can produce some kind of image.
* We use a nonvolatile flag to ensure that only one warning message
* appears per data segment.
*/
if (! cinfo->entropy->insufficient_data) {
WARNMS(cinfo, JWRN_HIT_MARKER);
cinfo->entropy->insufficient_data = TRUE;
}
/* Fill the buffer with zero bits */
get_buffer <<= MIN_GET_BITS - bits_left;
bits_left = MIN_GET_BITS;
}
}
/* Unload the local registers */
state->next_input_byte = next_input_byte;
state->bytes_in_buffer = bytes_in_buffer;
state->get_buffer = get_buffer;
state->bits_left = bits_left;
return TRUE;
}
/*
* Out-of-line code for Huffman code decoding.
* See jdhuff.h for info about usage.
*/
GLOBAL(int)
jpeg_huff_decode (bitread_working_state * state,
register bit_buf_type get_buffer, register int bits_left,
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(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(1);
l++;
}
/* Unload the local registers */
state->get_buffer = get_buffer;
state->bits_left = bits_left;
/* 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[ (int) (code + htbl->valoffset[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->bitstate.bits_left / 8;
entropy->bitstate.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;
/* Reset out-of-data flag, unless read_restart_marker left us smack up
* against a marker. In that case we will end up treating the next data
* segment as empty, and we can avoid producing bogus output pixels by
* leaving the flag set.
*/
if (cinfo->unread_marker == 0)
entropy->pub.insufficient_data = FALSE;
return TRUE;
}
/*
* 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, since we'll just re-assign them on the next call.)
*/
METHODDEF(boolean)
decode_mcu (j_decompress_ptr cinfo, JBLOCKROW *MCU_data)
{
huff_entropy_ptr entropy = (huff_entropy_ptr) cinfo->entropy;
int blkn;
BITREAD_STATE_VARS;
savable_state state;
/* 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;
}
/* If we've run out of data, just leave the MCU set to zeroes.
* This way, we return uniform gray for the remainder of the segment.
*/
if (! entropy->pub.insufficient_data) {
/* Load up working state */
BITREAD_LOAD_STATE(cinfo,entropy->bitstate);
ASSIGN_STATE(state, entropy->saved);
/* Outer loop handles each block in the MCU */
for (blkn = 0; blkn < cinfo->blocks_in_MCU; blkn++) {
JBLOCKROW block = MCU_data[blkn];
d_derived_tbl * dctbl = entropy->dc_cur_tbls[blkn];
d_derived_tbl * actbl = entropy->ac_cur_tbls[blkn];
register int s, k, r;
/* Decode a single block's worth of coefficients */
/* Section F.2.2.1: decode the DC coefficient difference */
HUFF_DECODE(s, br_state, dctbl, return FALSE, label1);
if (s) {
CHECK_BIT_BUFFER(br_state, s, return FALSE);
r = GET_BITS(s);
s = HUFF_EXTEND(r, s);
}
if (entropy->dc_needed[blkn]) {
/* Convert DC difference to actual value, update last_dc_val */
int ci = cinfo->MCU_membership[blkn];
s += state.last_dc_val[ci];
state.last_dc_val[ci] = s;
/* Output the DC coefficient (assumes jpeg_natural_order[0] = 0) */
(*block)[0] = (JCOEF) s;
}
if (entropy->ac_needed[blkn]) {
/* 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, br_state, actbl, return FALSE, label2);
r = s >> 4;
s &= 15;
if (s) {
k += r;
CHECK_BIT_BUFFER(br_state, s, return FALSE);
r = GET_BITS(s);
s = HUFF_EXTEND(r, s);
/* Output coefficient in natural (dezigzagged) order.
* Note: the extra entries in jpeg_natural_order[] will save us
* if k >= DCTSIZE2, which could happen if the data is corrupted.
*/
(*block)[jpeg_natural_order[k]] = (JCOEF) s;
} else {
if (r != 15)
break;
k += 15;
}
}
} else {
/* 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, br_state, actbl, return FALSE, label3);
r = s >> 4;
s &= 15;
if (s) {
k += r;
CHECK_BIT_BUFFER(br_state, s, return FALSE);
DROP_BITS(s);
} else {
if (r != 15)
break;
k += 15;
}
}
}
}
/* Completed MCU, so update state */
BITREAD_SAVE_STATE(cinfo,entropy->bitstate);
ASSIGN_STATE(entropy->saved, state);
}
/* 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;
}
}