/*
* reserved comment block
* DO NOT REMOVE OR ALTER!
*/
/*
*
* Copyright (C) 1995-1997, 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 for progressive JPEG.
*
* 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"
#ifdef D_PROGRESSIVE_SUPPORTED
/*
* Expanded entropy decoder object for progressive 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 {
/* 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
#else
#if MAX_COMPS_IN_SCAN == 4
#endif
#endif
typedef struct {
/* These fields are loaded into local variables at start of each MCU.
* In case of suspension, we exit WITHOUT updating them.
*/
/* These fields are NOT loaded into local working state. */
/* Pointers to derived tables (these workspaces have image lifespan) */
/* Forward declarations */
/*
* Initialize for a Huffman-compressed scan.
*/
METHODDEF(void)
{
int *coef_bit_ptr;
/* Validate scan parameters */
if (is_DC_band) {
} else {
/* AC scans may have only one component */
}
/* Successive approximation refinement scan: must have Al = Ah-1. */
}
/* Arguably the maximum Al value should be less than 13 for 8-bit precision,
* but the spec doesn't say so, and we try to be liberal about what we
* accept. Note: large Al values could result in out-of-range DC
* coefficients during early scans, leading to bizarre displays due to
* overflows in the IDCT math. But we won't crash.
*/
if (bad)
/* Update progression status, and verify that scan order is legal.
* Note that inter-scan inconsistencies are treated as warnings
* not fatal errors ... not clear if this is right way to behave.
*/
}
}
/* Select MCU decoding routine */
if (is_DC_band)
else
} else {
if (is_DC_band)
else
}
/* Make sure requested tables are present, and compute derived tables.
* We may build same derived table more than once, but it's not expensive.
*/
if (is_DC_band) {
}
} else {
/* remember the single active table */
}
/* Initialize DC predictions to 0 */
}
/* Initialize bitread state variables */
/* Initialize private state variables */
/* Initialize restart counter */
}
/*
* Figure F.12: extend sign bit.
* On some machines, a shift and add will be faster than a table lookup.
*/
#ifdef AVOID_TABLES
#else
{ 0, 0x0001, 0x0002, 0x0004, 0x0008, 0x0010, 0x0020, 0x0040, 0x0080,
0x0100, 0x0200, 0x0400, 0x0800, 0x1000, 0x2000, 0x4000 };
{ 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.
*/
{
int ci;
/* Throw away any unused bits remaining in bit buffer; */
/* include any full bytes in next_marker's count of discarded bytes */
/* Advance past the RSTn marker */
return FALSE;
/* Re-initialize DC predictions to 0 */
/* Re-init EOB run count, too */
/* Reset restart counter */
/* 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)
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.
*
* 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).
*/
{
register int s, r;
/* 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.
*/
/* Load up working state */
/* Outer loop handles each block in the MCU */
/* Decode a single block's worth of coefficients */
/* Section F.2.2.1: decode the DC coefficient difference */
if (s) {
r = GET_BITS(s);
s = HUFF_EXTEND(r, s);
}
/* Convert DC difference to actual value, update last_dc_val */
/* Scale and output the coefficient (assumes jpeg_natural_order[0]=0) */
}
/* Completed MCU, so update state */
}
/* Account for restart interval (no-op if not using restarts) */
return TRUE;
}
/*
* MCU decoding for AC initial scan (either spectral selection,
* or first pass of successive approximation).
*/
{
register int s, k, r;
unsigned int EOBRUN;
/* 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.
*/
/* Load up working state.
*/
/* 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 {
r = s >> 4;
s &= 15;
if (s) {
k += r;
r = GET_BITS(s);
s = HUFF_EXTEND(r, s);
/* Scale and output coefficient in natural (dezigzagged) order */
} 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 */
r = GET_BITS(r);
EOBRUN += r;
}
EOBRUN--; /* this band is processed at this moment */
break; /* force end-of-band */
}
}
}
}
/* Completed MCU, so update state */
}
/* Account for restart interval (no-op if not using restarts) */
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.
*/
{
int blkn;
/* 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 */
/* Outer loop handles each block in the MCU */
/* Encoded data is simply the next bit of the two's-complement DC value */
if (GET_BITS(1))
/* Note: since we use |=, repeating the assignment later is safe */
}
/* Completed MCU, so update state */
/* Account for restart interval (no-op if not using restarts) */
return TRUE;
}
/*
* MCU decoding for AC successive approximation refinement scan.
*/
{
register int s, k, r;
unsigned int EOBRUN;
int num_newnz;
/* 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.
*/
/* Load up working state */
/* There is always only one block per MCU */
/* 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 */
if (EOBRUN == 0) {
for (; k <= Se; k++) {
r = s >> 4;
s &= 15;
if (s) {
if (s != 1) /* size of new coef should always be 1 */
if (GET_BITS(1))
s = p1; /* newly nonzero coef is positive */
else
s = m1; /* newly nonzero coef is negative */
} else {
if (r != 15) {
if (r) {
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 {
if (*thiscoef != 0) {
if (GET_BITS(1)) {
if (*thiscoef >= 0)
else
}
}
} else {
if (--r < 0)
break; /* reached target zero coefficient */
}
k++;
} while (k <= Se);
if (s) {
/* Output newly nonzero coefficient */
/* Remember its position in case we have to suspend */
}
}
}
if (EOBRUN > 0) {
/* Scan any remaining coefficient positions after the end-of-band
* (the last newly nonzero coefficient, if any). Append a correction
* bit to each already-nonzero coefficient. A correction bit is 1
* if the absolute value of the coefficient must be increased.
*/
for (; k <= Se; k++) {
if (*thiscoef != 0) {
if (GET_BITS(1)) {
if (*thiscoef >= 0)
else
}
}
}
}
/* Count one block completed in EOB run */
EOBRUN--;
}
/* Completed MCU, so update state */
}
/* Account for restart interval (no-op if not using restarts) */
return TRUE;
/* Re-zero any output coefficients that we made newly nonzero */
while (num_newnz > 0)
return FALSE;
}
/*
* Module initialization routine for progressive Huffman entropy decoding.
*/
GLOBAL(void)
{
int *coef_bit_ptr;
int ci, i;
/* Mark derived tables unallocated */
for (i = 0; i < NUM_HUFF_TBLS; i++) {
}
/* Create progression status table */
for (i = 0; i < DCTSIZE2; i++)
*coef_bit_ptr++ = -1;
}
#endif /* D_PROGRESSIVE_SUPPORTED */