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