/*

* 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) {