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jdhuff.c
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jdhuff.c
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/*
* jdhuff.c
*
* Copyright (C) 1991-1997, Thomas G. Lane.
* Modified 2006-2009 by Guido Vollbeding.
* 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.
* Both sequential and progressive modes are supported in this single module.
*
* 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"
/* 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 maxcode[18]; /* largest code of length k (-1 if none) */
/* (maxcode[17] is a sentinel to ensure jpeg_huff_decode terminates) */
INT32 valoffset[17]; /* huffval[] offset for codes of length k */
/* valoffset[k] = huffval[] index of 1st symbol of code length k, less
* the smallest code of length k; so given a code of length k, the
* corresponding symbol is huffval[code + valoffset[k]]
*/
/* Link to public Huffman table (needed only in jpeg_huff_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;
/*
* Fetching the next N bits from the input stream is a time-critical operation
* for the Huffman decoders. We implement it with a combination of inline
* macros and out-of-line subroutines. Note that N (the number of bits
* demanded at one time) never exceeds 15 for JPEG use.
*
* 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, jpeg_fill_bit_buffer is called; it will attempt to fill get_buffer
* as full as possible (not just to the number of bits needed; this
* prefetching reduces the overhead cost of calling jpeg_fill_bit_buffer).
* Note that jpeg_fill_bit_buffer may return FALSE to indicate suspension.
* On TRUE return, jpeg_fill_bit_buffer guarantees that get_buffer contains
* at least the requested number of bits --- dummy zeroes are inserted if
* necessary.
*/
typedef INT32 bit_buf_type; /* type of bit-extraction buffer */
#define BIT_BUF_SIZE 32 /* size of buffer in bits */
/* If long is > 32 bits on your machine, and shifting/masking longs is
* reasonably fast, making bit_buf_type be long and setting BIT_BUF_SIZE
* appropriately should be a win. Unfortunately we can't define the size
* with something like #define BIT_BUF_SIZE (sizeof(bit_buf_type)*8)
* because not all machines measure sizeof in 8-bit bytes.
*/
typedef struct { /* Bitreading state saved across MCUs */
bit_buf_type get_buffer; /* current bit-extraction buffer */
int bits_left; /* # of unused bits in it */
} bitread_perm_state;
typedef struct { /* Bitreading working state within an MCU */
/* Current data source location */
/* We need a copy, rather than munging the original, in case of suspension */
const JOCTET * next_input_byte; /* => next byte to read from source */
size_t bytes_in_buffer; /* # of bytes remaining in source buffer */
/* Bit input buffer --- note these values are kept in register variables,
* not in this struct, inside the inner loops.
*/
bit_buf_type get_buffer; /* current bit-extraction buffer */
int bits_left; /* # of unused bits in it */
/* Pointer needed by jpeg_fill_bit_buffer. */
j_decompress_ptr cinfo; /* back link to decompress master record */
} bitread_working_state;
/* Macros to declare and load/save bitread local variables. */
#define BITREAD_STATE_VARS \
register bit_buf_type get_buffer; \
register int bits_left; \
bitread_working_state br_state
#define BITREAD_LOAD_STATE(cinfop,permstate) \
br_state.cinfo = cinfop; \
br_state.next_input_byte = cinfop->src->next_input_byte; \
br_state.bytes_in_buffer = cinfop->src->bytes_in_buffer; \
get_buffer = permstate.get_buffer; \
bits_left = permstate.bits_left;
#define BITREAD_SAVE_STATE(cinfop,permstate) \
cinfop->src->next_input_byte = br_state.next_input_byte; \
cinfop->src->bytes_in_buffer = br_state.bytes_in_buffer; \
permstate.get_buffer = get_buffer; \
permstate.bits_left = bits_left
/*
* 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.
* The variables get_buffer and bits_left are assumed to be locals,
* but the state struct might not be (jpeg_huff_decode needs this).
* CHECK_BIT_BUFFER(state,n,action);
* Ensure there are N bits in get_buffer; if suspend, take action.
* val = GET_BITS(n);
* Fetch next N bits.
* val = PEEK_BITS(n);
* Fetch next N bits without removing them from the buffer.
* DROP_BITS(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 (bits_left < (nbits)) { \
if (! jpeg_fill_bit_buffer(&(state),get_buffer,bits_left,nbits)) \
{ action; } \
get_buffer = (state).get_buffer; bits_left = (state).bits_left; } }
#define GET_BITS(nbits) \
(((int) (get_buffer >> (bits_left -= (nbits)))) & BIT_MASK(nbits))
#define PEEK_BITS(nbits) \
(((int) (get_buffer >> (bits_left - (nbits)))) & BIT_MASK(nbits))
#define DROP_BITS(nbits) \
(bits_left -= (nbits))
/*
* Code for extracting next Huffman-coded symbol from input bit stream.
* Again, this is time-critical and we make the main paths be macros.
*
* 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,
* which 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. jpeg_huff_decode returns -1 if forced to suspend.
*/
#define HUFF_DECODE(result,state,htbl,failaction,slowlabel) \
{ register int nb, look; \
if (bits_left < HUFF_LOOKAHEAD) { \
if (! jpeg_fill_bit_buffer(&state,get_buffer,bits_left, 0)) {failaction;} \
get_buffer = state.get_buffer; bits_left = state.bits_left; \
if (bits_left < HUFF_LOOKAHEAD) { \
nb = 1; goto slowlabel; \
} \
} \
look = PEEK_BITS(HUFF_LOOKAHEAD); \
if ((nb = htbl->look_nbits[look]) != 0) { \
DROP_BITS(nb); \
result = htbl->look_sym[look]; \
} else { \
nb = HUFF_LOOKAHEAD+1; \
slowlabel: \
if ((result=jpeg_huff_decode(&state,get_buffer,bits_left,htbl,nb)) < 0) \
{ failaction; } \
get_buffer = state.get_buffer; bits_left = state.bits_left; \
} \
}
/*
* 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 {
unsigned int EOBRUN; /* remaining EOBs in EOBRUN */
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).EOBRUN = (src).EOBRUN, \
(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. */
boolean insufficient_data; /* set TRUE after emitting warning */
unsigned int restarts_to_go; /* MCUs left in this restart interval */
/* Following two fields used only in progressive mode */
/* Pointers to derived tables (these workspaces have image lifespan) */
d_derived_tbl * derived_tbls[NUM_HUFF_TBLS];
d_derived_tbl * ac_derived_tbl; /* active table during an AC scan */
/* Following fields used only in sequential mode */
/* 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 */
int coef_limit[D_MAX_BLOCKS_IN_MCU];
} huff_entropy_decoder;
typedef huff_entropy_decoder * huff_entropy_ptr;
static const int jpeg_zigzag_order[8][8] = {
{ 0, 1, 5, 6, 14, 15, 27, 28 },
{ 2, 4, 7, 13, 16, 26, 29, 42 },
{ 3, 8, 12, 17, 25, 30, 41, 43 },
{ 9, 11, 18, 24, 31, 40, 44, 53 },
{ 10, 19, 23, 32, 39, 45, 52, 54 },
{ 20, 22, 33, 38, 46, 51, 55, 60 },
{ 21, 34, 37, 47, 50, 56, 59, 61 },
{ 35, 36, 48, 49, 57, 58, 62, 63 }
};
static const int jpeg_zigzag_order7[7][7] = {
{ 0, 1, 5, 6, 14, 15, 27 },
{ 2, 4, 7, 13, 16, 26, 28 },
{ 3, 8, 12, 17, 25, 29, 38 },
{ 9, 11, 18, 24, 30, 37, 39 },
{ 10, 19, 23, 31, 36, 40, 45 },
{ 20, 22, 32, 35, 41, 44, 46 },
{ 21, 33, 34, 42, 43, 47, 48 }
};
static const int jpeg_zigzag_order6[6][6] = {
{ 0, 1, 5, 6, 14, 15 },
{ 2, 4, 7, 13, 16, 25 },
{ 3, 8, 12, 17, 24, 26 },
{ 9, 11, 18, 23, 27, 32 },
{ 10, 19, 22, 28, 31, 33 },
{ 20, 21, 29, 30, 34, 35 }
};
static const int jpeg_zigzag_order5[5][5] = {
{ 0, 1, 5, 6, 14 },
{ 2, 4, 7, 13, 15 },
{ 3, 8, 12, 16, 21 },
{ 9, 11, 17, 20, 22 },
{ 10, 18, 19, 23, 24 }
};
static const int jpeg_zigzag_order4[4][4] = {
{ 0, 1, 5, 6 },
{ 2, 4, 7, 12 },
{ 3, 8, 11, 13 },
{ 9, 10, 14, 15 }
};
static const int jpeg_zigzag_order3[3][3] = {
{ 0, 1, 5 },
{ 2, 4, 6 },
{ 3, 7, 8 }
};
static const int jpeg_zigzag_order2[2][2] = {
{ 0, 1 },
{ 2, 3 }
};
/*
* Compute the derived values for a Huffman table.
* This routine also performs some validation checks on the table.
*/
LOCAL(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.
* 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
LOCAL(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 (! ((huff_entropy_ptr) cinfo->entropy)->insufficient_data) {
WARNMS(cinfo, JWRN_HIT_MARKER);
((huff_entropy_ptr) 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;
}
/*
* Figure F.12: extend sign bit.
* On some machines, a shift and sub will be faster than a table lookup.
*/
#ifdef AVOID_TABLES
#define BIT_MASK(nbits) ((1<<(nbits))-1)
#define HUFF_EXTEND(x,s) ((x) < (1<<((s)-1)) ? (x) - ((1<<(s))-1) : (x))
#else
#define BIT_MASK(nbits) bmask[nbits]
#define HUFF_EXTEND(x,s) ((x) <= bmask[(s) - 1] ? (x) - bmask[s] : (x))
static const int bmask[16] = /* bmask[n] is mask for n rightmost bits */
{ 0, 0x0001, 0x0003, 0x0007, 0x000F, 0x001F, 0x003F, 0x007F, 0x00FF,
0x01FF, 0x03FF, 0x07FF, 0x0FFF, 0x1FFF, 0x3FFF, 0x7FFF };
#endif /* AVOID_TABLES */
/*
* Out-of-line code for Huffman code decoding.
*/
LOCAL(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]) ];
}
/*
* 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;
/* Re-init EOB run count, too */
entropy->saved.EOBRUN = 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->insufficient_data = FALSE;
return TRUE;
}
/*
* Huffman MCU decoding.
* Each of these routines decodes and returns 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 IS INITIALLY ZEROED BY THE CALLER.
* (Wholesale zeroing is usually a little faster than retail...)
*
* We return 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
* spectral selection, since we'll just re-assign them on the next call.
* Successive approximation AC refinement has to be more careful, however.)
*/
/*
* MCU decoding for DC initial scan (either spectral selection,
* or first pass of successive approximation).
*/
METHODDEF(boolean)
decode_mcu_DC_first (j_decompress_ptr cinfo, JBLOCKROW *MCU_data)
{
huff_entropy_ptr entropy = (huff_entropy_ptr) cinfo->entropy;
int Al = cinfo->Al;
register int s, r;
int blkn, ci;
JBLOCKROW block;
BITREAD_STATE_VARS;
savable_state state;
d_derived_tbl * tbl;
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;
}
/* 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->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++) {
block = MCU_data[blkn];
ci = cinfo->MCU_membership[blkn];
compptr = cinfo->cur_comp_info[ci];
tbl = entropy->derived_tbls[compptr->dc_tbl_no];
/* Decode a single block's worth of coefficients */
/* Section F.2.2.1: decode the DC coefficient difference */
HUFF_DECODE(s, br_state, tbl, return FALSE, label1);
if (s) {
CHECK_BIT_BUFFER(br_state, s, return FALSE);
r = GET_BITS(s);
s = HUFF_EXTEND(r, s);
}
/* Convert DC difference to actual value, update last_dc_val */
s += state.last_dc_val[ci];
state.last_dc_val[ci] = s;
/* Scale and output the coefficient (assumes jpeg_natural_order[0]=0) */
(*block)[0] = (JCOEF) (s << Al);
}
/* 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;
}
/*
* MCU decoding for AC initial scan (either spectral selection,
* or first pass of successive approximation).
*/
METHODDEF(boolean)
decode_mcu_AC_first (j_decompress_ptr cinfo, JBLOCKROW *MCU_data)
{
huff_entropy_ptr entropy = (huff_entropy_ptr) cinfo->entropy;
register int s, k, r;
unsigned int EOBRUN;
int Se, Al;
const int * natural_order;
JBLOCKROW block;
BITREAD_STATE_VARS;
d_derived_tbl * tbl;
/* 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->insufficient_data) {
Se = cinfo->Se;
Al = cinfo->Al;
natural_order = cinfo->natural_order;
/* Load up working state.
* We can avoid loading/saving bitread state if in an EOB run.
*/
EOBRUN = entropy->saved.EOBRUN; /* only part of saved state we need */
/* There is always only one block per MCU */
if (EOBRUN > 0) /* if it's a band of zeroes... */
EOBRUN--; /* ...process it now (we do nothing) */
else {
BITREAD_LOAD_STATE(cinfo,entropy->bitstate);
block = MCU_data[0];
tbl = entropy->ac_derived_tbl;
for (k = cinfo->Ss; k <= Se; k++) {
HUFF_DECODE(s, br_state, tbl, 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);
/* Scale and output coefficient in natural (dezigzagged) order */
(*block)[natural_order[k]] = (JCOEF) (s << Al);
} else {
if (r == 15) { /* ZRL */
k += 15; /* skip 15 zeroes in band */
} else { /* EOBr, run length is 2^r + appended bits */
EOBRUN = 1 << r;
if (r) { /* EOBr, r > 0 */
CHECK_BIT_BUFFER(br_state, r, return FALSE);
r = GET_BITS(r);
EOBRUN += r;
}
EOBRUN--; /* this band is processed at this moment */
break; /* force end-of-band */
}
}
}
BITREAD_SAVE_STATE(cinfo,entropy->bitstate);
}
/* Completed MCU, so update state */
entropy->saved.EOBRUN = EOBRUN; /* only part of saved state we need */
}
/* Account for restart interval (no-op if not using restarts) */
entropy->restarts_to_go--;
return TRUE;
}
/*
* MCU decoding for DC successive approximation refinement scan.
* Note: we assume such scans can be multi-component, although the spec
* is not very clear on the point.
*/
METHODDEF(boolean)
decode_mcu_DC_refine (j_decompress_ptr cinfo, JBLOCKROW *MCU_data)
{
huff_entropy_ptr entropy = (huff_entropy_ptr) cinfo->entropy;
int p1 = 1 << cinfo->Al; /* 1 in the bit position being coded */
int blkn;
JBLOCKROW block;
BITREAD_STATE_VARS;
/* 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;
}
/* Not worth the cycles to check insufficient_data here,
* since we will not change the data anyway if we read zeroes.
*/
/* Load up working state */
BITREAD_LOAD_STATE(cinfo,entropy->bitstate);
/* Outer loop handles each block in the MCU */
for (blkn = 0; blkn < cinfo->blocks_in_MCU; blkn++) {
block = MCU_data[blkn];
/* Encoded data is simply the next bit of the two's-complement DC value */
CHECK_BIT_BUFFER(br_state, 1, return FALSE);
if (GET_BITS(1))
(*block)[0] |= p1;
/* Note: since we use |=, repeating the assignment later is safe */
}
/* Completed MCU, so update state */
BITREAD_SAVE_STATE(cinfo,entropy->bitstate);
/* Account for restart interval (no-op if not using restarts) */
entropy->restarts_to_go--;
return TRUE;
}
/*
* MCU decoding for AC successive approximation refinement scan.
*/
METHODDEF(boolean)
decode_mcu_AC_refine (j_decompress_ptr cinfo, JBLOCKROW *MCU_data)
{
huff_entropy_ptr entropy = (huff_entropy_ptr) cinfo->entropy;
register int s, k, r;
unsigned int EOBRUN;
int Se, p1, m1;
const int * natural_order;
JBLOCKROW block;
JCOEFPTR thiscoef;
BITREAD_STATE_VARS;
d_derived_tbl * tbl;
int num_newnz;
int newnz_pos[DCTSIZE2];
/* 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, don't modify the MCU.
*/
if (! entropy->insufficient_data) {
Se = cinfo->Se;
p1 = 1 << cinfo->Al; /* 1 in the bit position being coded */
m1 = (-1) << cinfo->Al; /* -1 in the bit position being coded */
natural_order = cinfo->natural_order;
/* Load up working state */
BITREAD_LOAD_STATE(cinfo,entropy->bitstate);
EOBRUN = entropy->saved.EOBRUN; /* only part of saved state we need */
/* There is always only one block per MCU */
block = MCU_data[0];
tbl = entropy->ac_derived_tbl;
/* If we are forced to suspend, we must undo the assignments to any newly
* nonzero coefficients in the block, because otherwise we'd get confused
* next time about which coefficients were already nonzero.
* But we need not undo addition of bits to already-nonzero coefficients;
* instead, we can test the current bit to see if we already did it.
*/
num_newnz = 0;
/* initialize coefficient loop counter to start of band */
k = cinfo->Ss;
if (EOBRUN == 0) {
for (; k <= Se; k++) {
HUFF_DECODE(s, br_state, tbl, goto undoit, label3);
r = s >> 4;
s &= 15;
if (s) {
if (s != 1) /* size of new coef should always be 1 */
WARNMS(cinfo, JWRN_HUFF_BAD_CODE);
CHECK_BIT_BUFFER(br_state, 1, goto undoit);
if (GET_BITS(1))
s = p1; /* newly nonzero coef is positive */
else
s = m1; /* newly nonzero coef is negative */
} else {
if (r != 15) {
EOBRUN = 1 << r; /* EOBr, run length is 2^r + appended bits */
if (r) {
CHECK_BIT_BUFFER(br_state, r, goto undoit);
r = GET_BITS(r);
EOBRUN += r;
}
break; /* rest of block is handled by EOB logic */
}
/* note s = 0 for processing ZRL */
}
/* Advance over already-nonzero coefs and r still-zero coefs,
* appending correction bits to the nonzeroes. A correction bit is 1
* if the absolute value of the coefficient must be increased.
*/
do {
thiscoef = *block + natural_order[k];
if (*thiscoef != 0) {
CHECK_BIT_BUFFER(br_state, 1, goto undoit);
if (GET_BITS(1)) {
if ((*thiscoef & p1) == 0) { /* do nothing if already set it */
if (*thiscoef >= 0)
*thiscoef += p1;
else
*thiscoef += m1;
}
}
} else {
if (--r < 0)
break; /* reached target zero coefficient */
}
k++;
} while (k <= Se);
if (s) {