arith_encode	(	j_compress_ptr	cinfo,
		unsigned char *	st,
		int	val
	)
Definition at line 219 of file jcarith.c.
Referenced by encode_mcu(), encode_mcu_AC_first(), encode_mcu_AC_refine(), encode_mcu_DC_first(), and encode_mcu_DC_refine().
{
  register arith_entropy_ptr e = (arith_entropy_ptr) cinfo->entropy;
  register unsigned char nl, nm;
  register INT32 qe, temp;
  register int sv;

  /* 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 */

  /* Encode & estimation procedures per sections D.1.4 & D.1.5 */
  e->a -= qe;
  if (val != (sv >> 7)) {
    /* Encode the less probable symbol */
    if (e->a >= qe) {
      /* If the interval size (qe) for the less probable symbol (LPS)
       * is larger than the interval size for the MPS, then exchange
       * the two symbols for coding efficiency, otherwise code the LPS
       * as usual: */
      e->c += e->a;
      e->a = qe;
    }
    *st = (sv & 0x80) ^ nl; /* Estimate_after_LPS */
  } else {
    /* Encode the more probable symbol */
    if (e->a >= 0x8000L)
      return;  /* A >= 0x8000 -> ready, no renormalization required */
    if (e->a < qe) {
      /* If the interval size (qe) for the less probable symbol (LPS)
       * is larger than the interval size for the MPS, then exchange
       * the two symbols for coding efficiency: */
      e->c += e->a;
      e->a = qe;
    }
    *st = (sv & 0x80) ^ nm; /* Estimate_after_MPS */
  }

  /* Renormalization & data output per section D.1.6 */
  do {
    e->a <<= 1;
    e->c <<= 1;
    if (--e->ct == 0) {
      /* Another byte is ready for output */
      temp = e->c >> 19;
      if (temp > 0xFF) {
    /* Handle overflow over all stacked 0xFF bytes */
    if (e->buffer >= 0) {
      if (e->zc)
        do emit_byte(0x00, cinfo);
        while (--e->zc);
      emit_byte(e->buffer + 1, cinfo);
      if (e->buffer + 1 == 0xFF)
        emit_byte(0x00, cinfo);
    }
    e->zc += e->sc;  /* carry-over converts stacked 0xFF bytes to 0x00 */
    e->sc = 0;
    /* Note: The 3 spacer bits in the C register guarantee
     * that the new buffer byte can't be 0xFF here
     * (see page 160 in the P&M JPEG book). */
    e->buffer = temp & 0xFF;  /* new output byte, might overflow later */
      } else if (temp == 0xFF) {
    ++e->sc;  /* stack 0xFF byte (which might overflow later) */
      } else {
    /* Output all stacked 0xFF bytes, they will not overflow any more */
    if (e->buffer == 0)
      ++e->zc;
    else if (e->buffer >= 0) {
      if (e->zc)
        do emit_byte(0x00, cinfo);
        while (--e->zc);
      emit_byte(e->buffer, cinfo);
    }
    if (e->sc) {
      if (e->zc)
        do emit_byte(0x00, cinfo);
        while (--e->zc);
      do {
        emit_byte(0xFF, cinfo);
        emit_byte(0x00, cinfo);
      } while (--e->sc);
    }
    e->buffer = temp & 0xFF;  /* new output byte (can still overflow) */
      }
      e->c &= 0x7FFFFL;
      e->ct += 8;
    }
  } while (e->a < 0x8000L);
}
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