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+/*
+ * jdarith.c
+ *
+ * Developed 1997 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];
+} 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.
+ * Note that we use one additional AC bin for codings with fixed
+ * probability (0.5), thus the minimum number for AC is 246.
+ *
+ * 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 get 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)
+{
+ extern const INT32 jaritab[];
+ 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.2:
+ * Qe values and probability estimation state machine
+ */
+ sv = *st;
+ qe = jaritab[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);
+
+ for (ci = 0; ci < cinfo->comps_in_scan; ci++) {
+ compptr = cinfo->cur_comp_info[ci];
+ /* Re-initialize statistics areas */
+ if (cinfo->progressive_mode == 0 || (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 == 0 || 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) == 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) (((INT32) 1 << cinfo->arith_dc_L[tbl]) >> 1))
+ entropy->dc_context[ci] = 0; /* zero diff category */
+ else if (m > (int) (((INT32) 1 << 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;
+
+ /* 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 */
+ entropy->ac_stats[tbl][245] = 0;
+ sign = arith_decode(cinfo, entropy->ac_stats[tbl] + 245);
+ 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) (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[4];
+ 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--;
+ }
+
+ 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++) {
+ st[0] = 0; /* use fixed probability estimation */
+ /* 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 = (-1) << cinfo->Al; /* -1 in the bit position being coded */
+
+ /* Establish EOBx (previous stage end-of-block) index */
+ for (kex = cinfo->Se + 1; kex > 1; kex--)
+ if ((*block)[jpeg_natural_order[kex - 1]]) 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 += m1;
+ else
+ *thiscoef += p1;
+ }
+ break;
+ }
+ if (arith_decode(cinfo, st + 1)) { /* newly nonzero coef */
+ entropy->ac_stats[tbl][245] = 0;
+ if (arith_decode(cinfo, entropy->ac_stats[tbl] + 245))
+ *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;
+
+ /* 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];
+ 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) (((INT32) 1 << cinfo->arith_dc_L[tbl]) >> 1))
+ entropy->dc_context[ci] = 0; /* zero diff category */
+ else if (m > (int) (((INT32) 1 << 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 < DCTSIZE2; 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) {
+ 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 */
+ entropy->ac_stats[tbl][245] = 0;
+ sign = arith_decode(cinfo, entropy->ac_stats[tbl] + 245);
+ 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)[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)
+ 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 because
+ * there are some baseline files out there with all zeroes in these bytes.
+ */
+ 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;
+ }
+
+ for (ci = 0; ci < cinfo->comps_in_scan; ci++) {
+ compptr = cinfo->cur_comp_info[ci];
+ /* Allocate & initialize requested statistics areas */
+ if (cinfo->progressive_mode == 0 || (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 == 0 || 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;
+ }
+
+ 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;
+ }
+}
generated by cgit v1.2.3 (git 2.39.1) at 2024-11-22 03:01:07 +0000