The Tor Browser: media/libjpeg/jdarith.c@b8a032363ba2 (annotated)

media/libjpeg/jdarith.c@b8a032363ba2 (annotated)

media/libjpeg/jdarith.c

Thu, 22 Jan 2015 13:21:57 +0100

author: Michael Schloh von Bennewitz <michael@schloh.com>
date: Thu, 22 Jan 2015 13:21:57 +0100
branch: TOR_BUG_9701
changeset 15: b8a032363ba2
permissions: -rw-r--r--

Incorporate requested changes from Mozilla in review:
https://bugzilla.mozilla.org/show_bug.cgi?id=1123480#c6

 /*
  * jdarith.c
  *
  * Developed 1997-2009 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 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)
 {
   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 = 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->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) ((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;
   /* 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) (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 = (-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 += m1;
 	  else
 	    *thiscoef += p1;
 	}
 	break;
       }
       if (arith_decode(cinfo, st + 1)) {	/* newly nonzero coef */
 	if (arith_decode(cinfo, entropy->fixed_bin))
 	  *thiscoef = m1;
 	else
 	  *thiscoef = p1;
 	break;
       }
       st += 3; k++;
       if (k > cinfo->Se) {
 	WARNMS(cinfo, JWRN_ARITH_BAD_CODE);
 	entropy->ct = -1;			/* spectral overflow */
 	return TRUE;
       }
     }
   }
   return TRUE;
 }
 /*
  * Decode one MCU's worth of arithmetic-compressed coefficients.
  */
 METHODDEF(boolean)
 decode_mcu (j_decompress_ptr cinfo, JBLOCKROW *MCU_data)
 {
   arith_entropy_ptr entropy = (arith_entropy_ptr) cinfo->entropy;
   jpeg_component_info * compptr;
   JBLOCKROW block;
   unsigned char *st;
   int blkn, ci, tbl, sign, k;
   int v, m;
   /* 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) ((1L << cinfo->arith_dc_L[tbl]) >> 1))
 	entropy->dc_context[ci] = 0;		   /* zero diff category */
       else if (m > (int) ((1L << cinfo->arith_dc_U[tbl]) >> 1))
 	entropy->dc_context[ci] = 12 + (sign * 4); /* large diff category */
       else
 	entropy->dc_context[ci] = 4 + (sign * 4);  /* small diff category */
       v = m;
       /* Figure F.24: Decoding the magnitude bit pattern of v */
       st += 14;
       while (m >>= 1)
 	if (arith_decode(cinfo, st)) v |= m;
       v += 1; if (sign) v = -v;
       entropy->last_dc_val[ci] += v;
     }
     (*block)[0] = (JCOEF) entropy->last_dc_val[ci];
     /* Sections F.2.4.2 & F.1.4.4.2: Decoding of AC coefficients */
     tbl = compptr->ac_tbl_no;
     /* Figure F.20: Decode_AC_coefficients */
     for (k = 1; k <= 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;
       (*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];
       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 != DCTSIZE2 - 1))
       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->Ss) {
       tbl = compptr->ac_tbl_no;
       if (tbl < 0 || tbl >= NUM_ARITH_TBLS)
 	ERREXIT1(cinfo, JERR_NO_ARITH_TABLE, tbl);
       if (entropy->ac_stats[tbl] == NULL)
 	entropy->ac_stats[tbl] = (unsigned char *) (*cinfo->mem->alloc_small)
 	  ((j_common_ptr) cinfo, JPOOL_IMAGE, AC_STAT_BINS);
       MEMZERO(entropy->ac_stats[tbl], AC_STAT_BINS);
     }
   }
   /* Initialize arithmetic decoding variables */
   entropy->c = 0;
   entropy->a = 0;
   entropy->ct = -16;	/* force reading 2 initial bytes to fill C */
   /* Initialize restart counter */
   entropy->restarts_to_go = cinfo->restart_interval;
 }
 /*
  * Module initialization routine for arithmetic entropy decoding.
  */
 GLOBAL(void)
 jinit_arith_decoder (j_decompress_ptr cinfo)
 {
   arith_entropy_ptr entropy;
   int i;
   entropy = (arith_entropy_ptr)
     (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE,
 				SIZEOF(arith_entropy_decoder));
   cinfo->entropy = (struct jpeg_entropy_decoder *) entropy;
   entropy->pub.start_pass = start_pass;
   /* Mark tables unallocated */
   for (i = 0; i < NUM_ARITH_TBLS; i++) {
     entropy->dc_stats[i] = NULL;
     entropy->ac_stats[i] = NULL;
   }
   /* Initialize index for fixed probability estimation */
   entropy->fixed_bin[0] = 113;
   if (cinfo->progressive_mode) {
     /* Create progression status table */
     int *coef_bit_ptr, ci;
     cinfo->coef_bits = (int (*)[DCTSIZE2])
       (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE,
 				  cinfo->num_components*DCTSIZE2*SIZEOF(int));
     coef_bit_ptr = & cinfo->coef_bits[0][0];
     for (ci = 0; ci < cinfo->num_components; ci++)
       for (i = 0; i < DCTSIZE2; i++)
 	*coef_bit_ptr++ = -1;
   }
 }

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media/libjpeg/jdarith.c@b8a032363ba2 (annotated)

media/libjpeg/jdarith.c