/* * jdarith.c * * Developed 1997-2019 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 portable arithmetic entropy decoding routines for JPEG * (implementing the ISO/IEC IS 10918-1 and CCITT Recommendation ITU-T T.81). * * Both sequential and progressive modes are supported in this single module. * * Suspension is not currently supported in this module. */ #define JPEG_INTERNALS #include "jinclude.h" #include "jpeglib.h" /* Expanded entropy decoder object for arithmetic decoding. */ typedef struct { struct jpeg_entropy_decoder pub; /* public fields */ INT32 c; /* C register, base of coding interval + input bit buffer */ INT32 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 GETJOCTET(*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 INT32 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.3(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)) { MEMZERO(entropy->dc_stats[compptr->dc_tbl_no], DC_STAT_BINS); /* Reset 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)) { MEMZERO(entropy->ac_stats[compptr->ac_tbl_no], 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) == (int) 0x8000U) { 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; } /* Scale and output the DC coefficient (assumes jpeg_natural_order[0]=0) */ (*block)[0] = (JCOEF) (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; 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; /* Sections F.2.4.2 & F.1.4.4.2: Decoding of AC coefficients */ /* Figure F.20: Decode_AC_coefficients */ k = cinfo->Ss - 1; do { st = entropy->ac_stats[tbl] + 3 * k; if (arith_decode(cinfo, st)) break; /* EOB flag */ for (;;) { k++; if (arith_decode(cinfo, st + 1)) break; st += 3; 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) == (int) 0x8000U) { 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); } while (k < cinfo->Se); 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) { arith_entropy_ptr entropy = (arith_entropy_ptr) cinfo->entropy; unsigned char *st; JCOEF p1; int 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; JCOEF 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 = -p1; /* -1 in the bit position being coded */ /* Establish EOBx (previous stage end-of-block) index */ kex = cinfo->Se; do { if ((*block)[natural_order[kex]]) break; } while (--kex); k = cinfo->Ss - 1; do { st = entropy->ac_stats[tbl] + 3 * k; 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; if (k >= cinfo->Se) { WARNMS(cinfo, JWRN_ARITH_BAD_CODE); entropy->ct = -1; /* spectral overflow */ return TRUE; } } } while (k < cinfo->Se); 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) == (int) 0x8000U) { 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 */ if (cinfo->lim_Se == 0) continue; tbl = compptr->ac_tbl_no; k = 0; /* Figure F.20: Decode_AC_coefficients */ do { st = entropy->ac_stats[tbl] + 3 * k; if (arith_decode(cinfo, st)) break; /* EOB flag */ for (;;) { k++; if (arith_decode(cinfo, st + 1)) break; st += 3; 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) == (int) 0x8000U) { 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; } while (k < cinfo->lim_Se); } 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; } /* * Finish up at the end of an arithmetic-compressed scan. */ METHODDEF(void) finish_pass (j_decompress_ptr cinfo) { /* no work necessary here */ } /* * 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 = &entropy->pub; entropy->pub.start_pass = start_pass; entropy->pub.finish_pass = finish_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; } }