| /* |
| * jdarith.c |
| * |
| * This file was part of the Independent JPEG Group's software: |
| * Developed 1997-2015 by Guido Vollbeding. |
| * libjpeg-turbo Modifications: |
| * Copyright (C) 2015-2020, 2022, D. R. Commander. |
| * For conditions of distribution and use, see the accompanying README.ijg |
| * file. |
| * |
| * This file contains portable arithmetic entropy encoding routines for JPEG |
| * (implementing Recommendation ITU-T T.81 | ISO/IEC 10918-1). |
| * |
| * Both sequential and progressive modes are supported in this single module. |
| * |
| * Suspension is not currently supported in this module. |
| * |
| * NOTE: All referenced figures are from |
| * Recommendation ITU-T T.81 (1992) | ISO/IEC 10918-1:1994. |
| */ |
| |
| #define JPEG_INTERNALS |
| #include "jinclude.h" |
| #include "jpeglib.h" |
| |
| |
| #define NEG_1 ((unsigned int)-1) |
| |
| |
| /* Expanded entropy decoder object for arithmetic decoding. */ |
| |
| typedef struct { |
| struct jpeg_entropy_decoder pub; /* public fields */ |
| |
| JLONG c; /* C register, base of coding interval + input bit buffer */ |
| JLONG a; /* A register, normalized size of coding interval */ |
| int ct; /* bit shift counter, # of bits left in bit buffer part of C */ |
| /* init: ct = -16 */ |
| /* run: ct = 0..7 */ |
| /* error: ct = -1 */ |
| int last_dc_val[MAX_COMPS_IN_SCAN]; /* last DC coef for each component */ |
| int dc_context[MAX_COMPS_IN_SCAN]; /* context index for DC conditioning */ |
| |
| unsigned int restarts_to_go; /* MCUs left in this restart interval */ |
| |
| /* Pointers to statistics areas (these workspaces have image lifespan) */ |
| unsigned char *dc_stats[NUM_ARITH_TBLS]; |
| unsigned char *ac_stats[NUM_ARITH_TBLS]; |
| |
| /* Statistics bin for coding with fixed probability 0.5 */ |
| unsigned char fixed_bin[4]; |
| } arith_entropy_decoder; |
| |
| typedef arith_entropy_decoder *arith_entropy_ptr; |
| |
| /* The following two definitions specify the allocation chunk size |
| * for the statistics area. |
| * According to sections F.1.4.4.1.3 and F.1.4.4.2, we need at least |
| * 49 statistics bins for DC, and 245 statistics bins for AC coding. |
| * |
| * We use a compact representation with 1 byte per statistics bin, |
| * thus the numbers directly represent byte sizes. |
| * This 1 byte per statistics bin contains the meaning of the MPS |
| * (more probable symbol) in the highest bit (mask 0x80), and the |
| * index into the probability estimation state machine table |
| * in the lower bits (mask 0x7F). |
| */ |
| |
| #define DC_STAT_BINS 64 |
| #define AC_STAT_BINS 256 |
| |
| |
| LOCAL(int) |
| get_byte(j_decompress_ptr cinfo) |
| /* Read next input byte; we do not support suspension in this module. */ |
| { |
| struct jpeg_source_mgr *src = cinfo->src; |
| |
| if (src->bytes_in_buffer == 0) |
| if (!(*src->fill_input_buffer) (cinfo)) |
| ERREXIT(cinfo, JERR_CANT_SUSPEND); |
| src->bytes_in_buffer--; |
| return *src->next_input_byte++; |
| } |
| |
| |
| /* |
| * The core arithmetic decoding routine (common in JPEG and JBIG). |
| * This needs to go as fast as possible. |
| * Machine-dependent optimization facilities |
| * are not utilized in this portable implementation. |
| * However, this code should be fairly efficient and |
| * may be a good base for further optimizations anyway. |
| * |
| * Return value is 0 or 1 (binary decision). |
| * |
| * Note: I've changed the handling of the code base & bit |
| * buffer register C compared to other implementations |
| * based on the standards layout & procedures. |
| * While it also contains both the actual base of the |
| * coding interval (16 bits) and the next-bits buffer, |
| * the cut-point between these two parts is floating |
| * (instead of fixed) with the bit shift counter CT. |
| * Thus, we also need only one (variable instead of |
| * fixed size) shift for the LPS/MPS decision, and |
| * we can do away with any renormalization update |
| * of C (except for new data insertion, of course). |
| * |
| * I've also introduced a new scheme for accessing |
| * the probability estimation state machine table, |
| * derived from Markus Kuhn's JBIG implementation. |
| */ |
| |
| LOCAL(int) |
| arith_decode(j_decompress_ptr cinfo, unsigned char *st) |
| { |
| register arith_entropy_ptr e = (arith_entropy_ptr)cinfo->entropy; |
| register unsigned char nl, nm; |
| register JLONG qe, temp; |
| register int sv, data; |
| |
| /* Renormalization & data input per section D.2.6 */ |
| while (e->a < 0x8000L) { |
| if (--e->ct < 0) { |
| /* Need to fetch next data byte */ |
| if (cinfo->unread_marker) |
| data = 0; /* stuff zero data */ |
| else { |
| data = get_byte(cinfo); /* read next input byte */ |
| if (data == 0xFF) { /* zero stuff or marker code */ |
| do data = get_byte(cinfo); |
| while (data == 0xFF); /* swallow extra 0xFF bytes */ |
| if (data == 0) |
| data = 0xFF; /* discard stuffed zero byte */ |
| else { |
| /* Note: Different from the Huffman decoder, hitting |
| * a marker while processing the compressed data |
| * segment is legal in arithmetic coding. |
| * The convention is to supply zero data |
| * then until decoding is complete. |
| */ |
| cinfo->unread_marker = data; |
| data = 0; |
| } |
| } |
| } |
| e->c = (e->c << 8) | data; /* insert data into C register */ |
| if ((e->ct += 8) < 0) /* update bit shift counter */ |
| /* Need more initial bytes */ |
| if (++e->ct == 0) |
| /* Got 2 initial bytes -> re-init A and exit loop */ |
| e->a = 0x8000L; /* => e->a = 0x10000L after loop exit */ |
| } |
| e->a <<= 1; |
| } |
| |
| /* Fetch values from our compact representation of Table D.2: |
| * Qe values and probability estimation state machine |
| */ |
| sv = *st; |
| qe = jpeg_aritab[sv & 0x7F]; /* => Qe_Value */ |
| nl = qe & 0xFF; qe >>= 8; /* Next_Index_LPS + Switch_MPS */ |
| nm = qe & 0xFF; qe >>= 8; /* Next_Index_MPS */ |
| |
| /* Decode & estimation procedures per sections D.2.4 & D.2.5 */ |
| temp = e->a - qe; |
| e->a = temp; |
| temp <<= e->ct; |
| if (e->c >= temp) { |
| e->c -= temp; |
| /* Conditional LPS (less probable symbol) exchange */ |
| if (e->a < qe) { |
| e->a = qe; |
| *st = (sv & 0x80) ^ nm; /* Estimate_after_MPS */ |
| } else { |
| e->a = qe; |
| *st = (sv & 0x80) ^ nl; /* Estimate_after_LPS */ |
| sv ^= 0x80; /* Exchange LPS/MPS */ |
| } |
| } else if (e->a < 0x8000L) { |
| /* Conditional MPS (more probable symbol) exchange */ |
| if (e->a < qe) { |
| *st = (sv & 0x80) ^ nl; /* Estimate_after_LPS */ |
| sv ^= 0x80; /* Exchange LPS/MPS */ |
| } else { |
| *st = (sv & 0x80) ^ nm; /* Estimate_after_MPS */ |
| } |
| } |
| |
| return sv >> 7; |
| } |
| |
| |
| /* |
| * Check for a restart marker & resynchronize decoder. |
| */ |
| |
| LOCAL(void) |
| process_restart(j_decompress_ptr cinfo) |
| { |
| arith_entropy_ptr entropy = (arith_entropy_ptr)cinfo->entropy; |
| int ci; |
| jpeg_component_info *compptr; |
| |
| /* Advance past the RSTn marker */ |
| if (!(*cinfo->marker->read_restart_marker) (cinfo)) |
| ERREXIT(cinfo, JERR_CANT_SUSPEND); |
| |
| /* Re-initialize 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)) { |
| memset(entropy->dc_stats[compptr->dc_tbl_no], 0, DC_STAT_BINS); |
| /* Reset DC predictions to 0 */ |
| entropy->last_dc_val[ci] = 0; |
| entropy->dc_context[ci] = 0; |
| } |
| if (!cinfo->progressive_mode || cinfo->Ss) { |
| memset(entropy->ac_stats[compptr->ac_tbl_no], 0, AC_STAT_BINS); |
| } |
| } |
| |
| /* Reset arithmetic decoding variables */ |
| entropy->c = 0; |
| entropy->a = 0; |
| entropy->ct = -16; /* force reading 2 initial bytes to fill C */ |
| |
| /* Reset restart counter */ |
| entropy->restarts_to_go = cinfo->restart_interval; |
| } |
| |
| |
| /* |
| * Arithmetic MCU decoding. |
| * Each of these routines decodes and returns one MCU's worth of |
| * arithmetic-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. |
| */ |
| |
| /* |
| * 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) |
| { |
| arith_entropy_ptr entropy = (arith_entropy_ptr)cinfo->entropy; |
| JBLOCKROW block; |
| unsigned char *st; |
| int blkn, ci, tbl, sign; |
| int v, m; |
| |
| /* 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 */ |
| |
| /* 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]; |
| tbl = cinfo->cur_comp_info[ci]->dc_tbl_no; |
| |
| /* Sections F.2.4.1 & F.1.4.4.1: Decoding of DC coefficients */ |
| |
| /* 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] = (entropy->last_dc_val[ci] + v) & 0xffff; |
| } |
| |
| /* Scale and output the DC coefficient (assumes jpeg_natural_order[0]=0) */ |
| (*block)[0] = (JCOEF)LEFT_SHIFT(entropy->last_dc_val[ci], cinfo->Al); |
| } |
| |
| 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) |
| { |
| arith_entropy_ptr entropy = (arith_entropy_ptr)cinfo->entropy; |
| JBLOCKROW block; |
| unsigned char *st; |
| int tbl, sign, k; |
| int v, m; |
| |
| /* 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 */ |
| |
| /* There is always only one block per MCU */ |
| block = MCU_data[0]; |
| tbl = cinfo->cur_comp_info[0]->ac_tbl_no; |
| |
| /* Sections F.2.4.2 & F.1.4.4.2: Decoding of AC coefficients */ |
| |
| /* Figure F.20: Decode_AC_coefficients */ |
| for (k = cinfo->Ss; k <= cinfo->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->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; |
| /* Scale and output coefficient in natural (dezigzagged) order */ |
| (*block)[jpeg_natural_order[k]] = (JCOEF)((unsigned)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; |
| |
| /* 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 */ |
| |
| /* 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 = (NEG_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)[jpeg_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 + jpeg_natural_order[k]; |
| if (*thiscoef) { /* previously nonzero coef */ |
| if (arith_decode(cinfo, st + 2)) { |
| if (*thiscoef < 0) |
| *thiscoef += (JCOEF)m1; |
| else |
| *thiscoef += (JCOEF)p1; |
| } |
| break; |
| } |
| if (arith_decode(cinfo, st + 1)) { /* newly nonzero coef */ |
| if (arith_decode(cinfo, entropy->fixed_bin)) |
| *thiscoef = (JCOEF)m1; |
| else |
| *thiscoef = (JCOEF)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; |
| |
| /* 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 */ |
| |
| /* Outer loop handles each block in the MCU */ |
| |
| for (blkn = 0; blkn < cinfo->blocks_in_MCU; blkn++) { |
| block = MCU_data ? MCU_data[blkn] : NULL; |
| 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] = (entropy->last_dc_val[ci] + v) & 0xffff; |
| } |
| |
| if (block) |
| (*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 <= DCTSIZE2 - 1; 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 > DCTSIZE2 - 1) { |
| 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; |
| if (block) |
| (*block)[jpeg_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 > DCTSIZE2 - 1) |
| 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]; |
| int *prev_coef_bit_ptr = |
| &cinfo->coef_bits[cindex + cinfo->num_components][0]; |
| if (cinfo->Ss && coef_bit_ptr[0] < 0) /* AC without prior DC scan */ |
| WARNMS2(cinfo, JWRN_BOGUS_PROGRESSION, cindex, 0); |
| for (coefi = MIN(cinfo->Ss, 1); coefi <= MAX(cinfo->Se, 9); coefi++) { |
| if (cinfo->input_scan_number > 1) |
| prev_coef_bit_ptr[coefi] = coef_bit_ptr[coefi]; |
| else |
| prev_coef_bit_ptr[coefi] = 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->Se != DCTSIZE2 - 1 || |
| cinfo->Ah != 0 || cinfo->Al != 0) |
| 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); |
| memset(entropy->dc_stats[tbl], 0, DC_STAT_BINS); |
| /* Initialize DC predictions to 0 */ |
| entropy->last_dc_val[ci] = 0; |
| entropy->dc_context[ci] = 0; |
| } |
| if (!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); |
| memset(entropy->ac_stats[tbl], 0, AC_STAT_BINS); |
| } |
| } |
| |
| /* Initialize arithmetic decoding variables */ |
| entropy->c = 0; |
| entropy->a = 0; |
| entropy->ct = -16; /* force reading 2 initial bytes to fill C */ |
| entropy->pub.insufficient_data = FALSE; |
| |
| /* 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 * 2 * 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; |
| } |
| } |
