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773 lines
23 KiB
773 lines
23 KiB
5 years ago
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/*
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* jdarith.c
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*
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* Developed 1997-2009 by Guido Vollbeding.
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* This file is part of the Independent JPEG Group's software.
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* For conditions of distribution and use, see the accompanying README file.
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*
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* This file contains portable arithmetic entropy decoding routines for JPEG
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* (implementing the ISO/IEC IS 10918-1 and CCITT Recommendation ITU-T T.81).
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*
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* Both sequential and progressive modes are supported in this single module.
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*
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* Suspension is not currently supported in this module.
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*/
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#define JPEG_INTERNALS
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#include "jinclude.h"
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#include "jpeglib.h"
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/* Expanded entropy decoder object for arithmetic decoding. */
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typedef struct {
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struct jpeg_entropy_decoder pub; /* public fields */
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INT32 c; /* C register, base of coding interval + input bit buffer */
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INT32 a; /* A register, normalized size of coding interval */
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int ct; /* bit shift counter, # of bits left in bit buffer part of C */
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/* init: ct = -16 */
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/* run: ct = 0..7 */
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/* error: ct = -1 */
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int last_dc_val[MAX_COMPS_IN_SCAN]; /* last DC coef for each component */
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int dc_context[MAX_COMPS_IN_SCAN]; /* context index for DC conditioning */
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unsigned int restarts_to_go; /* MCUs left in this restart interval */
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/* Pointers to statistics areas (these workspaces have image lifespan) */
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unsigned char * dc_stats[NUM_ARITH_TBLS];
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unsigned char * ac_stats[NUM_ARITH_TBLS];
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/* Statistics bin for coding with fixed probability 0.5 */
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unsigned char fixed_bin[4];
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} arith_entropy_decoder;
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typedef arith_entropy_decoder * arith_entropy_ptr;
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/* The following two definitions specify the allocation chunk size
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* for the statistics area.
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* According to sections F.1.4.4.1.3 and F.1.4.4.2, we need at least
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* 49 statistics bins for DC, and 245 statistics bins for AC coding.
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*
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* We use a compact representation with 1 byte per statistics bin,
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* thus the numbers directly represent byte sizes.
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* This 1 byte per statistics bin contains the meaning of the MPS
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* (more probable symbol) in the highest bit (mask 0x80), and the
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* index into the probability estimation state machine table
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* in the lower bits (mask 0x7F).
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*/
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#define DC_STAT_BINS 64
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#define AC_STAT_BINS 256
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LOCAL(int)
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get_byte (j_decompress_ptr cinfo)
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/* Read next input byte; we do not support suspension in this module. */
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{
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struct jpeg_source_mgr * src = cinfo->src;
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if (src->bytes_in_buffer == 0)
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if (! (*src->fill_input_buffer) (cinfo))
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ERREXIT(cinfo, JERR_CANT_SUSPEND);
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src->bytes_in_buffer--;
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return GETJOCTET(*src->next_input_byte++);
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}
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/*
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* The core arithmetic decoding routine (common in JPEG and JBIG).
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* This needs to go as fast as possible.
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* Machine-dependent optimization facilities
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* are not utilized in this portable implementation.
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* However, this code should be fairly efficient and
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* may be a good base for further optimizations anyway.
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*
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* Return value is 0 or 1 (binary decision).
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*
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* Note: I've changed the handling of the code base & bit
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* buffer register C compared to other implementations
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* based on the standards layout & procedures.
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* While it also contains both the actual base of the
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* coding interval (16 bits) and the next-bits buffer,
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* the cut-point between these two parts is floating
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* (instead of fixed) with the bit shift counter CT.
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* Thus, we also need only one (variable instead of
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* fixed size) shift for the LPS/MPS decision, and
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* we can get away with any renormalization update
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* of C (except for new data insertion, of course).
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*
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* I've also introduced a new scheme for accessing
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* the probability estimation state machine table,
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* derived from Markus Kuhn's JBIG implementation.
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*/
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LOCAL(int)
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arith_decode (j_decompress_ptr cinfo, unsigned char *st)
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{
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arith_entropy_ptr e = (arith_entropy_ptr) cinfo->entropy;
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unsigned char nl, nm;
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INT32 qe, temp;
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int sv, data;
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/* Renormalization & data input per section D.2.6 */
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while (e->a < 0x8000L) {
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if (--e->ct < 0) {
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/* Need to fetch next data byte */
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if (cinfo->unread_marker)
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data = 0; /* stuff zero data */
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else {
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data = get_byte(cinfo); /* read next input byte */
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if (data == 0xFF) { /* zero stuff or marker code */
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do data = get_byte(cinfo);
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while (data == 0xFF); /* swallow extra 0xFF bytes */
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if (data == 0)
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data = 0xFF; /* discard stuffed zero byte */
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else {
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/* Note: Different from the Huffman decoder, hitting
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* a marker while processing the compressed data
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* segment is legal in arithmetic coding.
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* The convention is to supply zero data
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* then until decoding is complete.
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*/
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cinfo->unread_marker = data;
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data = 0;
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}
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}
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}
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e->c = (e->c << 8) | data; /* insert data into C register */
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if ((e->ct += 8) < 0) /* update bit shift counter */
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/* Need more initial bytes */
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if (++e->ct == 0)
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/* Got 2 initial bytes -> re-init A and exit loop */
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e->a = 0x8000L; /* => e->a = 0x10000L after loop exit */
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}
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e->a <<= 1;
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}
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/* Fetch values from our compact representation of Table D.2:
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* Qe values and probability estimation state machine
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*/
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sv = *st;
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qe = jpeg_aritab[sv & 0x7F]; /* => Qe_Value */
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nl = qe & 0xFF; qe >>= 8; /* Next_Index_LPS + Switch_MPS */
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nm = qe & 0xFF; qe >>= 8; /* Next_Index_MPS */
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/* Decode & estimation procedures per sections D.2.4 & D.2.5 */
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temp = e->a - qe;
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e->a = temp;
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temp <<= e->ct;
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if (e->c >= temp) {
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e->c -= temp;
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/* Conditional LPS (less probable symbol) exchange */
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if (e->a < qe) {
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e->a = qe;
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*st = (sv & 0x80) ^ nm; /* Estimate_after_MPS */
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} else {
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e->a = qe;
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*st = (sv & 0x80) ^ nl; /* Estimate_after_LPS */
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sv ^= 0x80; /* Exchange LPS/MPS */
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}
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} else if (e->a < 0x8000L) {
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/* Conditional MPS (more probable symbol) exchange */
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if (e->a < qe) {
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*st = (sv & 0x80) ^ nl; /* Estimate_after_LPS */
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sv ^= 0x80; /* Exchange LPS/MPS */
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} else {
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*st = (sv & 0x80) ^ nm; /* Estimate_after_MPS */
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}
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}
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return sv >> 7;
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}
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/*
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* Check for a restart marker & resynchronize decoder.
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*/
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LOCAL(void)
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process_restart (j_decompress_ptr cinfo)
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{
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arith_entropy_ptr entropy = (arith_entropy_ptr) cinfo->entropy;
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int ci;
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jpeg_component_info * compptr;
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/* Advance past the RSTn marker */
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if (! (*cinfo->marker->read_restart_marker) (cinfo))
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ERREXIT(cinfo, JERR_CANT_SUSPEND);
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/* Re-initialize statistics areas */
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for (ci = 0; ci < cinfo->comps_in_scan; ci++) {
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compptr = cinfo->cur_comp_info[ci];
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if (! cinfo->progressive_mode || (cinfo->Ss == 0 && cinfo->Ah == 0)) {
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MEMZERO(entropy->dc_stats[compptr->dc_tbl_no], DC_STAT_BINS);
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/* Reset DC predictions to 0 */
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entropy->last_dc_val[ci] = 0;
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entropy->dc_context[ci] = 0;
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}
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if ((! cinfo->progressive_mode && cinfo->lim_Se) ||
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(cinfo->progressive_mode && cinfo->Ss)) {
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MEMZERO(entropy->ac_stats[compptr->ac_tbl_no], AC_STAT_BINS);
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}
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}
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/* Reset arithmetic decoding variables */
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entropy->c = 0;
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entropy->a = 0;
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entropy->ct = -16; /* force reading 2 initial bytes to fill C */
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/* Reset restart counter */
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entropy->restarts_to_go = cinfo->restart_interval;
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}
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/*
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* Arithmetic MCU decoding.
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* Each of these routines decodes and returns one MCU's worth of
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* arithmetic-compressed coefficients.
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* The coefficients are reordered from zigzag order into natural array order,
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* but are not dequantized.
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*
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* The i'th block of the MCU is stored into the block pointed to by
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* MCU_data[i]. WE ASSUME THIS AREA IS INITIALLY ZEROED BY THE CALLER.
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*/
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/*
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* MCU decoding for DC initial scan (either spectral selection,
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* or first pass of successive approximation).
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*/
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METHODDEF(boolean)
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decode_mcu_DC_first (j_decompress_ptr cinfo, JBLOCKROW *MCU_data)
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{
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arith_entropy_ptr entropy = (arith_entropy_ptr) cinfo->entropy;
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JBLOCKROW block;
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unsigned char *st;
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int blkn, ci, tbl, sign;
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int v, m;
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/* Process restart marker if needed */
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if (cinfo->restart_interval) {
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if (entropy->restarts_to_go == 0)
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process_restart(cinfo);
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entropy->restarts_to_go--;
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}
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if (entropy->ct == -1) return TRUE; /* if error do nothing */
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/* Outer loop handles each block in the MCU */
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for (blkn = 0; blkn < cinfo->blocks_in_MCU; blkn++) {
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block = MCU_data[blkn];
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ci = cinfo->MCU_membership[blkn];
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tbl = cinfo->cur_comp_info[ci]->dc_tbl_no;
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/* Sections F.2.4.1 & F.1.4.4.1: Decoding of DC coefficients */
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/* Table F.4: Point to statistics bin S0 for DC coefficient coding */
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st = entropy->dc_stats[tbl] + entropy->dc_context[ci];
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/* Figure F.19: Decode_DC_DIFF */
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if (arith_decode(cinfo, st) == 0)
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entropy->dc_context[ci] = 0;
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else {
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/* Figure F.21: Decoding nonzero value v */
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/* Figure F.22: Decoding the sign of v */
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sign = arith_decode(cinfo, st + 1);
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st += 2; st += sign;
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/* Figure F.23: Decoding the magnitude category of v */
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if ((m = arith_decode(cinfo, st)) != 0) {
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st = entropy->dc_stats[tbl] + 20; /* Table F.4: X1 = 20 */
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while (arith_decode(cinfo, st)) {
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if ((m <<= 1) == 0x8000) {
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WARNMS(cinfo, JWRN_ARITH_BAD_CODE);
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entropy->ct = -1; /* magnitude overflow */
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return TRUE;
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}
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st += 1;
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}
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}
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/* Section F.1.4.4.1.2: Establish dc_context conditioning category */
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if (m < (int) ((1L << cinfo->arith_dc_L[tbl]) >> 1))
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entropy->dc_context[ci] = 0; /* zero diff category */
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else if (m > (int) ((1L << cinfo->arith_dc_U[tbl]) >> 1))
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entropy->dc_context[ci] = 12 + (sign * 4); /* large diff category */
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else
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entropy->dc_context[ci] = 4 + (sign * 4); /* small diff category */
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v = m;
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/* Figure F.24: Decoding the magnitude bit pattern of v */
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st += 14;
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while (m >>= 1)
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if (arith_decode(cinfo, st)) v |= m;
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v += 1; if (sign) v = -v;
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entropy->last_dc_val[ci] += v;
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}
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/* Scale and output the DC coefficient (assumes jpeg_natural_order[0]=0) */
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(*block)[0] = (JCOEF) (entropy->last_dc_val[ci] << cinfo->Al);
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}
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return TRUE;
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}
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/*
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* MCU decoding for AC initial scan (either spectral selection,
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* or first pass of successive approximation).
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*/
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METHODDEF(boolean)
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decode_mcu_AC_first (j_decompress_ptr cinfo, JBLOCKROW *MCU_data)
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{
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arith_entropy_ptr entropy = (arith_entropy_ptr) cinfo->entropy;
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JBLOCKROW block;
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unsigned char *st;
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int tbl, sign, k;
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int v, m;
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const int * natural_order;
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/* Process restart marker if needed */
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if (cinfo->restart_interval) {
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if (entropy->restarts_to_go == 0)
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process_restart(cinfo);
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entropy->restarts_to_go--;
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}
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if (entropy->ct == -1) return TRUE; /* if error do nothing */
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natural_order = cinfo->natural_order;
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/* There is always only one block per MCU */
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block = MCU_data[0];
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tbl = cinfo->cur_comp_info[0]->ac_tbl_no;
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/* Sections F.2.4.2 & F.1.4.4.2: Decoding of AC coefficients */
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/* Figure F.20: Decode_AC_coefficients */
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for (k = cinfo->Ss; k <= cinfo->Se; k++) {
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st = entropy->ac_stats[tbl] + 3 * (k - 1);
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if (arith_decode(cinfo, st)) break; /* EOB flag */
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while (arith_decode(cinfo, st + 1) == 0) {
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st += 3; k++;
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if (k > cinfo->Se) {
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|
|
WARNMS(cinfo, JWRN_ARITH_BAD_CODE);
|
||
|
|
entropy->ct = -1; /* spectral overflow */
|
||
|
|
return TRUE;
|
||
|
|
}
|
||
|
|
}
|
||
|
|
/* Figure F.21: Decoding nonzero value v */
|
||
|
|
/* Figure F.22: Decoding the sign of v */
|
||
|
|
sign = arith_decode(cinfo, entropy->fixed_bin);
|
||
|
|
st += 2;
|
||
|
|
/* Figure F.23: Decoding the magnitude category of v */
|
||
|
|
if ((m = arith_decode(cinfo, st)) != 0) {
|
||
|
|
if (arith_decode(cinfo, st)) {
|
||
|
|
m <<= 1;
|
||
|
|
st = entropy->ac_stats[tbl] +
|
||
|
|
(k <= cinfo->arith_ac_K[tbl] ? 189 : 217);
|
||
|
|
while (arith_decode(cinfo, st)) {
|
||
|
|
if ((m <<= 1) == 0x8000) {
|
||
|
|
WARNMS(cinfo, JWRN_ARITH_BAD_CODE);
|
||
|
|
entropy->ct = -1; /* magnitude overflow */
|
||
|
|
return TRUE;
|
||
|
|
}
|
||
|
|
st += 1;
|
||
|
|
}
|
||
|
|
}
|
||
|
|
}
|
||
|
|
v = m;
|
||
|
|
/* Figure F.24: Decoding the magnitude bit pattern of v */
|
||
|
|
st += 14;
|
||
|
|
while (m >>= 1)
|
||
|
|
if (arith_decode(cinfo, st)) v |= m;
|
||
|
|
v += 1; if (sign) v = -v;
|
||
|
|
/* Scale and output coefficient in natural (dezigzagged) order */
|
||
|
|
(*block)[natural_order[k]] = (JCOEF) (v << cinfo->Al);
|
||
|
|
}
|
||
|
|
|
||
|
|
return TRUE;
|
||
|
|
}
|
||
|
|
|
||
|
|
|
||
|
|
/*
|
||
|
|
* MCU decoding for DC successive approximation refinement scan.
|
||
|
|
*/
|
||
|
|
|
||
|
|
METHODDEF(boolean)
|
||
|
|
decode_mcu_DC_refine (j_decompress_ptr cinfo, JBLOCKROW *MCU_data)
|
||
|
|
{
|
||
|
|
arith_entropy_ptr entropy = (arith_entropy_ptr) cinfo->entropy;
|
||
|
|
unsigned char *st;
|
||
|
|
int p1, blkn;
|
||
|
|
|
||
|
|
/* Process restart marker if needed */
|
||
|
|
if (cinfo->restart_interval) {
|
||
|
|
if (entropy->restarts_to_go == 0)
|
||
|
|
process_restart(cinfo);
|
||
|
|
entropy->restarts_to_go--;
|
||
|
|
}
|
||
|
|
|
||
|
|
st = entropy->fixed_bin; /* use fixed probability estimation */
|
||
|
|
p1 = 1 << cinfo->Al; /* 1 in the bit position being coded */
|
||
|
|
|
||
|
|
/* Outer loop handles each block in the MCU */
|
||
|
|
|
||
|
|
for (blkn = 0; blkn < cinfo->blocks_in_MCU; blkn++) {
|
||
|
|
/* Encoded data is simply the next bit of the two's-complement DC value */
|
||
|
|
if (arith_decode(cinfo, st))
|
||
|
|
MCU_data[blkn][0][0] |= p1;
|
||
|
|
}
|
||
|
|
|
||
|
|
return TRUE;
|
||
|
|
}
|
||
|
|
|
||
|
|
|
||
|
|
/*
|
||
|
|
* MCU decoding for AC successive approximation refinement scan.
|
||
|
|
*/
|
||
|
|
|
||
|
|
METHODDEF(boolean)
|
||
|
|
decode_mcu_AC_refine (j_decompress_ptr cinfo, JBLOCKROW *MCU_data)
|
||
|
|
{
|
||
|
|
arith_entropy_ptr entropy = (arith_entropy_ptr) cinfo->entropy;
|
||
|
|
JBLOCKROW block;
|
||
|
|
JCOEFPTR thiscoef;
|
||
|
|
unsigned char *st;
|
||
|
|
int tbl, k, kex;
|
||
|
|
int p1, m1;
|
||
|
|
const int * natural_order;
|
||
|
|
|
||
|
|
/* Process restart marker if needed */
|
||
|
|
if (cinfo->restart_interval) {
|
||
|
|
if (entropy->restarts_to_go == 0)
|
||
|
|
process_restart(cinfo);
|
||
|
|
entropy->restarts_to_go--;
|
||
|
|
}
|
||
|
|
|
||
|
|
if (entropy->ct == -1) return TRUE; /* if error do nothing */
|
||
|
|
|
||
|
|
natural_order = cinfo->natural_order;
|
||
|
|
|
||
|
|
/* There is always only one block per MCU */
|
||
|
|
block = MCU_data[0];
|
||
|
|
tbl = cinfo->cur_comp_info[0]->ac_tbl_no;
|
||
|
|
|
||
|
|
p1 = 1 << cinfo->Al; /* 1 in the bit position being coded */
|
||
|
|
m1 = (-1) << cinfo->Al; /* -1 in the bit position being coded */
|
||
|
|
|
||
|
|
/* Establish EOBx (previous stage end-of-block) index */
|
||
|
|
for (kex = cinfo->Se; kex > 0; kex--)
|
||
|
|
if ((*block)[natural_order[kex]]) break;
|
||
|
|
|
||
|
|
for (k = cinfo->Ss; k <= cinfo->Se; k++) {
|
||
|
|
st = entropy->ac_stats[tbl] + 3 * (k - 1);
|
||
|
|
if (k > kex)
|
||
|
|
if (arith_decode(cinfo, st)) break; /* EOB flag */
|
||
|
|
for (;;) {
|
||
|
|
thiscoef = *block + natural_order[k];
|
||
|
|
if (*thiscoef) { /* previously nonzero coef */
|
||
|
|
if (arith_decode(cinfo, st + 2)) {
|
||
|
|
if (*thiscoef < 0)
|
||
|
|
*thiscoef += m1;
|
||
|
|
else
|
||
|
|
*thiscoef += p1;
|
||
|
|
}
|
||
|
|
break;
|
||
|
|
}
|
||
|
|
if (arith_decode(cinfo, st + 1)) { /* newly nonzero coef */
|
||
|
|
if (arith_decode(cinfo, entropy->fixed_bin))
|
||
|
|
*thiscoef = m1;
|
||
|
|
else
|
||
|
|
*thiscoef = p1;
|
||
|
|
break;
|
||
|
|
}
|
||
|
|
st += 3; k++;
|
||
|
|
if (k > cinfo->Se) {
|
||
|
|
WARNMS(cinfo, JWRN_ARITH_BAD_CODE);
|
||
|
|
entropy->ct = -1; /* spectral overflow */
|
||
|
|
return TRUE;
|
||
|
|
}
|
||
|
|
}
|
||
|
|
}
|
||
|
|
|
||
|
|
return TRUE;
|
||
|
|
}
|
||
|
|
|
||
|
|
|
||
|
|
/*
|
||
|
|
* Decode one MCU's worth of arithmetic-compressed coefficients.
|
||
|
|
*/
|
||
|
|
|
||
|
|
METHODDEF(boolean)
|
||
|
|
decode_mcu (j_decompress_ptr cinfo, JBLOCKROW *MCU_data)
|
||
|
|
{
|
||
|
|
arith_entropy_ptr entropy = (arith_entropy_ptr) cinfo->entropy;
|
||
|
|
jpeg_component_info * compptr;
|
||
|
|
JBLOCKROW block;
|
||
|
|
unsigned char *st;
|
||
|
|
int blkn, ci, tbl, sign, k;
|
||
|
|
int v, m;
|
||
|
|
const int * natural_order;
|
||
|
|
|
||
|
|
/* Process restart marker if needed */
|
||
|
|
if (cinfo->restart_interval) {
|
||
|
|
if (entropy->restarts_to_go == 0)
|
||
|
|
process_restart(cinfo);
|
||
|
|
entropy->restarts_to_go--;
|
||
|
|
}
|
||
|
|
|
||
|
|
if (entropy->ct == -1) return TRUE; /* if error do nothing */
|
||
|
|
|
||
|
|
natural_order = cinfo->natural_order;
|
||
|
|
|
||
|
|
/* 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];
|
||
|
|
|
||
|
|
/* Sections F.2.4.1 & F.1.4.4.1: Decoding of DC coefficients */
|
||
|
|
|
||
|
|
tbl = compptr->dc_tbl_no;
|
||
|
|
|
||
|
|
/* Table F.4: Point to statistics bin S0 for DC coefficient coding */
|
||
|
|
st = entropy->dc_stats[tbl] + entropy->dc_context[ci];
|
||
|
|
|
||
|
|
/* Figure F.19: Decode_DC_DIFF */
|
||
|
|
if (arith_decode(cinfo, st) == 0)
|
||
|
|
entropy->dc_context[ci] = 0;
|
||
|
|
else {
|
||
|
|
/* Figure F.21: Decoding nonzero value v */
|
||
|
|
/* Figure F.22: Decoding the sign of v */
|
||
|
|
sign = arith_decode(cinfo, st + 1);
|
||
|
|
st += 2; st += sign;
|
||
|
|
/* Figure F.23: Decoding the magnitude category of v */
|
||
|
|
if ((m = arith_decode(cinfo, st)) != 0) {
|
||
|
|
st = entropy->dc_stats[tbl] + 20; /* Table F.4: X1 = 20 */
|
||
|
|
while (arith_decode(cinfo, st)) {
|
||
|
|
if ((m <<= 1) == 0x8000) {
|
||
|
|
WARNMS(cinfo, JWRN_ARITH_BAD_CODE);
|
||
|
|
entropy->ct = -1; /* magnitude overflow */
|
||
|
|
return TRUE;
|
||
|
|
}
|
||
|
|
st += 1;
|
||
|
|
}
|
||
|
|
}
|
||
|
|
/* Section F.1.4.4.1.2: Establish dc_context conditioning category */
|
||
|
|
if (m < (int) ((1L << cinfo->arith_dc_L[tbl]) >> 1))
|
||
|
|
entropy->dc_context[ci] = 0; /* zero diff category */
|
||
|
|
else if (m > (int) ((1L << cinfo->arith_dc_U[tbl]) >> 1))
|
||
|
|
entropy->dc_context[ci] = 12 + (sign * 4); /* large diff category */
|
||
|
|
else
|
||
|
|
entropy->dc_context[ci] = 4 + (sign * 4); /* small diff category */
|
||
|
|
v = m;
|
||
|
|
/* Figure F.24: Decoding the magnitude bit pattern of v */
|
||
|
|
st += 14;
|
||
|
|
while (m >>= 1)
|
||
|
|
if (arith_decode(cinfo, st)) v |= m;
|
||
|
|
v += 1; if (sign) v = -v;
|
||
|
|
entropy->last_dc_val[ci] += v;
|
||
|
|
}
|
||
|
|
|
||
|
|
(*block)[0] = (JCOEF) entropy->last_dc_val[ci];
|
||
|
|
|
||
|
|
/* Sections F.2.4.2 & F.1.4.4.2: Decoding of AC coefficients */
|
||
|
|
|
||
|
|
tbl = compptr->ac_tbl_no;
|
||
|
|
|
||
|
|
/* Figure F.20: Decode_AC_coefficients */
|
||
|
|
for (k = 1; k <= cinfo->lim_Se; k++) {
|
||
|
|
st = entropy->ac_stats[tbl] + 3 * (k - 1);
|
||
|
|
if (arith_decode(cinfo, st)) break; /* EOB flag */
|
||
|
|
while (arith_decode(cinfo, st + 1) == 0) {
|
||
|
|
st += 3; k++;
|
||
|
|
if (k > cinfo->lim_Se) {
|
||
|
|
WARNMS(cinfo, JWRN_ARITH_BAD_CODE);
|
||
|
|
entropy->ct = -1; /* spectral overflow */
|
||
|
|
return TRUE;
|
||
|
|
}
|
||
|
|
}
|
||
|
|
/* Figure F.21: Decoding nonzero value v */
|
||
|
|
/* Figure F.22: Decoding the sign of v */
|
||
|
|
sign = arith_decode(cinfo, entropy->fixed_bin);
|
||
|
|
st += 2;
|
||
|
|
/* Figure F.23: Decoding the magnitude category of v */
|
||
|
|
if ((m = arith_decode(cinfo, st)) != 0) {
|
||
|
|
if (arith_decode(cinfo, st)) {
|
||
|
|
m <<= 1;
|
||
|
|
st = entropy->ac_stats[tbl] +
|
||
|
|
(k <= cinfo->arith_ac_K[tbl] ? 189 : 217);
|
||
|
|
while (arith_decode(cinfo, st)) {
|
||
|
|
if ((m <<= 1) == 0x8000) {
|
||
|
|
WARNMS(cinfo, JWRN_ARITH_BAD_CODE);
|
||
|
|
entropy->ct = -1; /* magnitude overflow */
|
||
|
|
return TRUE;
|
||
|
|
}
|
||
|
|
st += 1;
|
||
|
|
}
|
||
|
|
}
|
||
|
|
}
|
||
|
|
v = m;
|
||
|
|
/* Figure F.24: Decoding the magnitude bit pattern of v */
|
||
|
|
st += 14;
|
||
|
|
while (m >>= 1)
|
||
|
|
if (arith_decode(cinfo, st)) v |= m;
|
||
|
|
v += 1; if (sign) v = -v;
|
||
|
|
(*block)[natural_order[k]] = (JCOEF) v;
|
||
|
|
}
|
||
|
|
}
|
||
|
|
|
||
|
|
return TRUE;
|
||
|
|
}
|
||
|
|
|
||
|
|
|
||
|
|
/*
|
||
|
|
* Initialize for an arithmetic-compressed scan.
|
||
|
|
*/
|
||
|
|
|
||
|
|
METHODDEF(void)
|
||
|
|
start_pass (j_decompress_ptr cinfo)
|
||
|
|
{
|
||
|
|
arith_entropy_ptr entropy = (arith_entropy_ptr) cinfo->entropy;
|
||
|
|
int ci, tbl;
|
||
|
|
jpeg_component_info * compptr;
|
||
|
|
|
||
|
|
if (cinfo->progressive_mode) {
|
||
|
|
/* Validate progressive scan parameters */
|
||
|
|
if (cinfo->Ss == 0) {
|
||
|
|
if (cinfo->Se != 0)
|
||
|
|
goto bad;
|
||
|
|
} else {
|
||
|
|
/* need not check Ss/Se < 0 since they came from unsigned bytes */
|
||
|
|
if (cinfo->Se < cinfo->Ss || cinfo->Se > cinfo->lim_Se)
|
||
|
|
goto bad;
|
||
|
|
/* AC scans may have only one component */
|
||
|
|
if (cinfo->comps_in_scan != 1)
|
||
|
|
goto bad;
|
||
|
|
}
|
||
|
|
if (cinfo->Ah != 0) {
|
||
|
|
/* Successive approximation refinement scan: must have Al = Ah-1. */
|
||
|
|
if (cinfo->Ah-1 != cinfo->Al)
|
||
|
|
goto bad;
|
||
|
|
}
|
||
|
|
if (cinfo->Al > 13) { /* need not check for < 0 */
|
||
|
|
bad:
|
||
|
|
ERREXIT4(cinfo, JERR_BAD_PROGRESSION,
|
||
|
|
cinfo->Ss, cinfo->Se, cinfo->Ah, cinfo->Al);
|
||
|
|
}
|
||
|
|
/* 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.
|
||
|
|
*/
|
||
|
|
for (ci = 0; ci < cinfo->comps_in_scan; ci++) {
|
||
|
|
int coefi, cindex = cinfo->cur_comp_info[ci]->component_index;
|
||
|
|
int *coef_bit_ptr = & cinfo->coef_bits[cindex][0];
|
||
|
|
if (cinfo->Ss && coef_bit_ptr[0] < 0) /* AC without prior DC scan */
|
||
|
|
WARNMS2(cinfo, JWRN_BOGUS_PROGRESSION, cindex, 0);
|
||
|
|
for (coefi = cinfo->Ss; coefi <= cinfo->Se; coefi++) {
|
||
|
|
int expected = (coef_bit_ptr[coefi] < 0) ? 0 : coef_bit_ptr[coefi];
|
||
|
|
if (cinfo->Ah != expected)
|
||
|
|
WARNMS2(cinfo, JWRN_BOGUS_PROGRESSION, cindex, coefi);
|
||
|
|
coef_bit_ptr[coefi] = cinfo->Al;
|
||
|
|
}
|
||
|
|
}
|
||
|
|
/* Select MCU decoding routine */
|
||
|
|
if (cinfo->Ah == 0) {
|
||
|
|
if (cinfo->Ss == 0)
|
||
|
|
entropy->pub.decode_mcu = decode_mcu_DC_first;
|
||
|
|
else
|
||
|
|
entropy->pub.decode_mcu = decode_mcu_AC_first;
|
||
|
|
} else {
|
||
|
|
if (cinfo->Ss == 0)
|
||
|
|
entropy->pub.decode_mcu = decode_mcu_DC_refine;
|
||
|
|
else
|
||
|
|
entropy->pub.decode_mcu = decode_mcu_AC_refine;
|
||
|
|
}
|
||
|
|
} else {
|
||
|
|
/* 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.
|
||
|
|
*/
|
||
|
|
if (cinfo->Ss != 0 || cinfo->Ah != 0 || cinfo->Al != 0 ||
|
||
|
|
(cinfo->Se < DCTSIZE2 && cinfo->Se != cinfo->lim_Se))
|
||
|
|
WARNMS(cinfo, JWRN_NOT_SEQUENTIAL);
|
||
|
|
/* Select MCU decoding routine */
|
||
|
|
entropy->pub.decode_mcu = decode_mcu;
|
||
|
|
}
|
||
|
|
|
||
|
|
/* Allocate & initialize requested statistics areas */
|
||
|
|
for (ci = 0; ci < cinfo->comps_in_scan; ci++) {
|
||
|
|
compptr = cinfo->cur_comp_info[ci];
|
||
|
|
if (! cinfo->progressive_mode || (cinfo->Ss == 0 && cinfo->Ah == 0)) {
|
||
|
|
tbl = compptr->dc_tbl_no;
|
||
|
|
if (tbl < 0 || tbl >= NUM_ARITH_TBLS)
|
||
|
|
ERREXIT1(cinfo, JERR_NO_ARITH_TABLE, tbl);
|
||
|
|
if (entropy->dc_stats[tbl] == NULL)
|
||
|
|
entropy->dc_stats[tbl] = (unsigned char *) (*cinfo->mem->alloc_small)
|
||
|
|
((j_common_ptr) cinfo, JPOOL_IMAGE, DC_STAT_BINS);
|
||
|
|
MEMZERO(entropy->dc_stats[tbl], DC_STAT_BINS);
|
||
|
|
/* Initialize DC predictions to 0 */
|
||
|
|
entropy->last_dc_val[ci] = 0;
|
||
|
|
entropy->dc_context[ci] = 0;
|
||
|
|
}
|
||
|
|
if ((! cinfo->progressive_mode && cinfo->lim_Se) ||
|
||
|
|
(cinfo->progressive_mode && cinfo->Ss)) {
|
||
|
|
tbl = compptr->ac_tbl_no;
|
||
|
|
if (tbl < 0 || tbl >= NUM_ARITH_TBLS)
|
||
|
|
ERREXIT1(cinfo, JERR_NO_ARITH_TABLE, tbl);
|
||
|
|
if (entropy->ac_stats[tbl] == NULL)
|
||
|
|
entropy->ac_stats[tbl] = (unsigned char *) (*cinfo->mem->alloc_small)
|
||
|
|
((j_common_ptr) cinfo, JPOOL_IMAGE, AC_STAT_BINS);
|
||
|
|
MEMZERO(entropy->ac_stats[tbl], AC_STAT_BINS);
|
||
|
|
}
|
||
|
|
}
|
||
|
|
|
||
|
|
/* Initialize arithmetic decoding variables */
|
||
|
|
entropy->c = 0;
|
||
|
|
entropy->a = 0;
|
||
|
|
entropy->ct = -16; /* force reading 2 initial bytes to fill C */
|
||
|
|
|
||
|
|
/* Initialize restart counter */
|
||
|
|
entropy->restarts_to_go = cinfo->restart_interval;
|
||
|
|
}
|
||
|
|
|
||
|
|
|
||
|
|
/*
|
||
|
|
* Module initialization routine for arithmetic entropy decoding.
|
||
|
|
*/
|
||
|
|
|
||
|
|
GLOBAL(void)
|
||
|
|
jinit_arith_decoder (j_decompress_ptr cinfo)
|
||
|
|
{
|
||
|
|
arith_entropy_ptr entropy;
|
||
|
|
int i;
|
||
|
|
|
||
|
|
entropy = (arith_entropy_ptr)
|
||
|
|
(*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE,
|
||
|
|
SIZEOF(arith_entropy_decoder));
|
||
|
|
cinfo->entropy = (struct jpeg_entropy_decoder *) entropy;
|
||
|
|
entropy->pub.start_pass = start_pass;
|
||
|
|
|
||
|
|
/* Mark tables unallocated */
|
||
|
|
for (i = 0; i < NUM_ARITH_TBLS; i++) {
|
||
|
|
entropy->dc_stats[i] = NULL;
|
||
|
|
entropy->ac_stats[i] = NULL;
|
||
|
|
}
|
||
|
|
|
||
|
|
/* Initialize index for fixed probability estimation */
|
||
|
|
entropy->fixed_bin[0] = 113;
|
||
|
|
|
||
|
|
if (cinfo->progressive_mode) {
|
||
|
|
/* Create progression status table */
|
||
|
|
int *coef_bit_ptr, ci;
|
||
|
|
cinfo->coef_bits = (int (*)[DCTSIZE2])
|
||
|
|
(*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE,
|
||
|
|
cinfo->num_components*DCTSIZE2*SIZEOF(int));
|
||
|
|
coef_bit_ptr = & cinfo->coef_bits[0][0];
|
||
|
|
for (ci = 0; ci < cinfo->num_components; ci++)
|
||
|
|
for (i = 0; i < DCTSIZE2; i++)
|
||
|
|
*coef_bit_ptr++ = -1;
|
||
|
|
}
|
||
|
|
}
|