jdarith.c File Reference

#include "jinclude.h"
#include "jpeglib.h"

Include dependency graph for jdarith.c:

Go to the source code of this file.

Classes
struct	arith_entropy_decoder

Macros
#define	JPEG_INTERNALS
#define	DC_STAT_BINS   64
#define	AC_STAT_BINS   256

Typedefs
typedef arith_entropy_decoder *	arith_entropy_ptr

Functions
	get_byte (j_decompress_ptr cinfo)
	arith_decode (j_decompress_ptr cinfo, unsigned char *st)
	process_restart (j_decompress_ptr cinfo)
	decode_mcu_DC_first (j_decompress_ptr cinfo, JBLOCKROW *MCU_data)
	decode_mcu_AC_first (j_decompress_ptr cinfo, JBLOCKROW *MCU_data)
	decode_mcu_DC_refine (j_decompress_ptr cinfo, JBLOCKROW *MCU_data)
	decode_mcu_AC_refine (j_decompress_ptr cinfo, JBLOCKROW *MCU_data)
	decode_mcu (j_decompress_ptr cinfo, JBLOCKROW *MCU_data)
	start_pass (j_decompress_ptr cinfo)
	finish_pass (j_decompress_ptr cinfo)
	jinit_arith_decoder (j_decompress_ptr cinfo)

Macro Definition Documentation

AC_STAT_BINS

#define AC_STAT_BINS   256

Definition at line 61 of file jdarith.c.

DC_STAT_BINS

#define DC_STAT_BINS   64

Definition at line 60 of file jdarith.c.

JPEG_INTERNALS

#define JPEG_INTERNALS

Definition at line 16 of file jdarith.c.

Typedef Documentation

arith_entropy_ptr

typedef arith_entropy_decoder* arith_entropy_ptr

Definition at line 45 of file jdarith.c.

Function Documentation

arith_decode()

arith_decode	(	j_decompress_ptr	cinfo,
		unsigned char *	st
	)

Definition at line 106 of file jdarith.c.

{
  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;
}

Referenced by decode_mcu(), decode_mcu_AC_first(), decode_mcu_AC_refine(), decode_mcu_DC_first(), and decode_mcu_DC_refine().

decode_mcu()

decode_mcu	(	j_decompress_ptr	cinfo,
		JBLOCKROW *	MCU_data
	)

Definition at line 512 of file jdarith.c.

{
  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;
}

Referenced by start_pass().

decode_mcu_AC_first()

decode_mcu_AC_first	(	j_decompress_ptr	cinfo,
		JBLOCKROW *	MCU_data
	)

Definition at line 321 of file jdarith.c.

{
  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;
}

Referenced by start_pass().

decode_mcu_AC_refine()

decode_mcu_AC_refine	(	j_decompress_ptr	cinfo,
		JBLOCKROW *	MCU_data
	)

Definition at line 437 of file jdarith.c.

{
  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;
}

Referenced by start_pass().

decode_mcu_DC_first()

decode_mcu_DC_first	(	j_decompress_ptr	cinfo,
		JBLOCKROW *	MCU_data
	)

Definition at line 242 of file jdarith.c.

{
  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;
}

Referenced by start_pass().

decode_mcu_DC_refine()

decode_mcu_DC_refine	(	j_decompress_ptr	cinfo,
		JBLOCKROW *	MCU_data
	)

Definition at line 403 of file jdarith.c.

{
  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;
}

Referenced by start_pass().

finish_pass()

finish_pass

(

j_decompress_ptr

cinfo

)

Definition at line 754 of file jdarith.c.

{
  /* no work necessary here */
}

Referenced by jinit_arith_decoder().

get_byte()

get_byte

(

j_decompress_ptr

cinfo

)

Definition at line 65 of file jdarith.c.

{
  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++);
}

jinit_arith_decoder()

jinit_arith_decoder

(

j_decompress_ptr

cinfo

)

Definition at line 765 of file jdarith.c.

{
  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;
  }
}

Referenced by master_selection(), and transdecode_master_selection().

process_restart()

process_restart

(

j_decompress_ptr

cinfo

)

Definition at line 190 of file jdarith.c.

{
  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;
}

Referenced by decode_mcu(), decode_mcu_AC_first(), decode_mcu_AC_refine(), decode_mcu_DC_first(), and decode_mcu_DC_refine().

start_pass()

start_pass

(

j_decompress_ptr

cinfo

)

Definition at line 644 of file jdarith.c.

{
  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;
}

Referenced by jinit_arith_decoder().