jdarith.c

It is possible that certain products which can be built using this software modules might form inve

    /* 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;
  }
}