/************************************************************************ * *  sac.c, part of tmn (TMN encoder) * *  Copyright (C) 1997  University of BC, Canada * *  Contacts:  *  Michael Gallant                   <mikeg@ee.ubc.ca> *  Guy Cote                          <guyc@ee.ubc.ca> *  Berna Erol                        <bernae@ee.ubc.ca> * *  UBC Image Processing Laboratory   http://www.ee.ubc.ca/image *  2356 Main Mall                    tel.: +1 604 822 4051 *  Vancouver BC Canada V6T1Z4        fax.: +1 604 822 5949 * *  Copyright (C) 1995, 1996  Telenor R&D, Norway * *  Contacts: *  Robert Danielsen                  <Robert.Danielsen@nta.no> * *  Telenor Research and Development  http://www.nta.no/brukere/DVC/ *  P.O.Box 83                        tel.:   +47 63 84 84 00 *  N-2007 Kjeller, Norway            fax.:   +47 63 81 00 76 * ************************************************************************//* Disclaimer of Warranty *  * These software programs are available to the user without any license fee * or royalty on an "as is" basis. The University of British Columbia * disclaims any and all warranties, whether express, implied, or * statuary, including any implied warranties or merchantability or of * fitness for a particular purpose.  In no event shall the * copyright-holder be liable for any incidental, punitive, or * consequential damages of any kind whatsoever arising from the use of * these programs. *  * This disclaimer of warranty extends to the user of these programs and * user's customers, employees, agents, transferees, successors, and * assigns. *  * The University of British Columbia does not represent or warrant that the * programs furnished hereunder are free of infringement of any * third-party patents. *  * Commercial implementations of H.263, including shareware, are subject to * royalty fees to patent holders.  Many of these patents are general * enough such that they are unavoidable regardless of implementation * design. *  *//********************************************************************* * * SAC Encoder Module * Algorithm as specified in H263 (Annex E) *         (c) BT Labs 1995 * * Author: Pat Mulroy <pmulroy@visual.bt.co.uk> * *********************************************************************/#include <stdio.h>#include "sim.h"#define   q1    16384#define   q2    32768#define   q3    49152#define   top   65535static long low = 0, high = top, opposite_bits = 0, length = 0, zerorun = 0;/********************************************************************* * *      Name:           AR_Encode * *      Description:    Encodes a symbol using syntax based arithmetic *        coding. Algorithm specified in H.263 (Annex E). * *      Input:          Array holding cumulative frequency data. *        Index into specific cumulative frequency array. *                      Static data for encoding endpoints. * *      Returns:        Number of bits used while encoding symbol. * *      Side Effects:   Modifies low, high, length and opposite_bits *        variables. * *      Author:         pmulroy@visual.bt.co.uk * *********************************************************************/int AR_Encode (int index, int cumul_freq[]){  int bitcount = 0;  if (index < 0)    return -1;                  /* Escape Code */  length = high - low + 1;  high = low - 1 + (length * cumul_freq[index]) / cumul_freq[0];  low += (length * cumul_freq[index + 1]) / cumul_freq[0];  for (;;)  {    if (high < q2)    {      bitcount += bit_opp_bits (0);    } else if (low >= q2)    {      bitcount += bit_opp_bits (1);      low -= q2;      high -= q2;    } else if (low >= q1 && high < q3)    {      opposite_bits += 1;      low -= q1;      high -= q1;    } else      break;    low *= 2;    high = 2 * high + 1;  }  return bitcount;}int bit_opp_bits (int bit)      /* Output a bit and the following opposite                                 * bits */{  int bitcount = 0;  bitcount = bit_in_psc_layer (bit);  while (opposite_bits > 0)  {    bitcount += bit_in_psc_layer (!bit);    opposite_bits--;  }  return bitcount;}/********************************************************************* * *      Name:           encoder_flush * *      Description:    Completes arithmetic coding stream before any *        fixed length codes are transmitted. * *      Input:          None * *      Returns:        Number of bits used. * *      Side Effects:   Resets low, high, zerorun and opposite_bits *        variables. * *      Author:         pmulroy@visual.bt.co.uk * *********************************************************************/int encoder_flush (){  int bitcount = 0;  if (trace)    fprintf (tf, "encoder_flush:\n");  opposite_bits++;  if (low < q1)  {    bitcount += bit_opp_bits (0);  } else  {    bitcount += bit_opp_bits (1);  }  low = 0;  high = top;  zerorun = 0;  return bitcount;}/********************************************************************* * *      Name:           bit_in_psc_layer * *      Description:    Inserts a bit into output bitstream and avoids *        picture start code emulation by stuffing a one *        bit. * *      Input:          Bit to be output. * *      Returns:        Nothing * *      Side Effects:   Updates zerorun variable. * *      Author:         pmulroy@visual.bt.co.uk * *********************************************************************/int bit_in_psc_layer (int bit){  void putbits (int, int);  int bitcount = 0;  if (zerorun > 13)  {    if (trace)      fprintf (tf, "PSC emulation ... Bit stuffed.\n");    putbits (1, 1);    bitcount++;    zerorun = 0;  }  putbits (1, bit);  bitcount++;  if (bit)    zerorun = 0;  else    zerorun++;  return bitcount;}/********************************************************************* * *      Name:           indexfn * *      Description:    Translates between symbol value and symbol *        index. * *      Input:          Symbol value, index table, max number of *        values. * *      Returns:        Index into cumulative frequency tables or *        escape code. * *      Side Effects:   none * *      Author:         pmulroy@visual.bt.co.uk * *********************************************************************/int indexfn (int value, int table[], int max){  int n = 0;  while (1)  {    if (table[n++] == value)      return n - 1;    if (n > max)      return -1;  }}