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	  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;
}


/*
 * 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->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;
}


/*
 * 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;