arithmeticdecoder.cpp

Go to the documentation of this file.

/*
===============================================================================
 
  FILE:  arithmeticdecoder.cpp
  
  CONTENTS:
      
    A modular C++ wrapper for an adapted version of Amir Said's FastAC Code.
    see: http://www.cipr.rpi.edu/~said/FastAC.html
 
  PROGRAMMERS:
 
    martin.isenburg@gmail.com
 
  COPYRIGHT:
 
    (c) 2011, Martin Isenburg, LASSO - tools to catch reality
 
    This is free software; you can redistribute and/or modify it under the
    terms of the GNU Lesser General Licence as published by the Free Software
    Foundation. See the COPYING file for more information.
 
    This software is distributed WITHOUT ANY WARRANTY and without even the
    implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
  
  CHANGE HISTORY:
  
    see header file
  
===============================================================================
*/
 
// - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
//                                                                           -
// Fast arithmetic coding implementation                                     -
// -> 32-bit variables, 32-bit product, periodic updates, table decoding     -
//                                                                           -
// - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
//                                                                           -
// Version 1.00  -  April 25, 2004                                           -
//                                                                           -
// - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
//                                                                           -
//                                  WARNING                                  -
//                                 =========                                 -
//                                                                           -
// The only purpose of this program is to demonstrate the basic principles   -
// of arithmetic coding. It is provided as is, without any express or        -
// implied warranty, without even the warranty of fitness for any particular -
// purpose, or that the implementations are correct.                         -
//                                                                           -
// Permission to copy and redistribute this code is hereby granted, provided -
// that this warning and copyright notices are not removed or altered.       -
//                                                                           -
// Copyright (c) 2004 by Amir Said (said@ieee.org) &                         -
//                       William A. Pearlman (pearlw@ecse.rpi.edu)           -
//                                                                           -
// - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
//                                                                           -
// A description of the arithmetic coding method used here is available in   -
//                                                                           -
// Lossless Compression Handbook, ed. K. Sayood                              -
// Chapter 5: Arithmetic Coding (A. Said), pp. 101-152, Academic Press, 2003 -
//                                                                           -
// A. Said, Introduction to Arithetic Coding Theory and Practice             -
// HP Labs report HPL-2004-76  -  http://www.hpl.hp.com/techreports/         -
//                                                                           -
// - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
 
#include "arithmeticdecoder.hpp"
 
#include <string.h>
#include <assert.h>
 
#include "arithmeticmodel.hpp"
 
ArithmeticDecoder::ArithmeticDecoder()
{
  instream = 0;
}
 
BOOL ArithmeticDecoder::init(ByteStreamIn* instream)
{
  if (instream == 0) return FALSE;
  this->instream = instream;
  length = AC__MaxLength;
  value = (instream->getByte() << 24);
  value |= (instream->getByte() << 16);
  value |= (instream->getByte() << 8);
  value |= (instream->getByte());
  return TRUE;
}
 
void ArithmeticDecoder::done()
{
  instream = 0;
}
 
EntropyModel* ArithmeticDecoder::createBitModel()
{
  ArithmeticBitModel* m = new ArithmeticBitModel();
  return (EntropyModel*)m;
}
 
void ArithmeticDecoder::initBitModel(EntropyModel* model)
{
  ArithmeticBitModel* m = (ArithmeticBitModel*)model;
  m->init();
}
 
void ArithmeticDecoder::destroyBitModel(EntropyModel* model)
{
  ArithmeticBitModel* m = (ArithmeticBitModel*)model;
  delete m;
}
 
EntropyModel* ArithmeticDecoder::createSymbolModel(U32 n)
{
  ArithmeticModel* m = new ArithmeticModel(n, false);
  return (EntropyModel*)m;
}
 
void ArithmeticDecoder::initSymbolModel(EntropyModel* model, U32 *table)
{
  ArithmeticModel* m = (ArithmeticModel*)model;
  m->init(table);
}
 
void ArithmeticDecoder::destroySymbolModel(EntropyModel* model)
{
  ArithmeticModel* m = (ArithmeticModel*)model;
  delete m;
}
 
U32 ArithmeticDecoder::decodeBit(EntropyModel* model)
{
  ArithmeticBitModel* m = (ArithmeticBitModel*)model;
  U32 x = m->bit_0_prob * (length >> BM__LengthShift);       // product l x p0
  U32 sym = (value >= x);                                          // decision
                                                    // update & shift interval
  if (sym == 0) {
    length  = x;
    ++m->bit_0_count;
  }
  else {
    value  -= x;                                  // shifted interval base = 0
    length -= x;
  }
 
  if (length < AC__MinLength) renorm_dec_interval();        // renormalization
  if (--m->bits_until_update == 0) m->update();       // periodic model update
 
  return sym;                                         // return data bit value
}
 
U32 ArithmeticDecoder::decodeSymbol(EntropyModel* model)
{
  ArithmeticModel* m = (ArithmeticModel*)model;
  U32 n, sym, x, y = length;
 
  if (m->decoder_table) {             // use table look-up for faster decoding
 
    unsigned dv = value / (length >>= DM__LengthShift);
    unsigned t = dv >> m->table_shift;
 
    sym = m->decoder_table[t];      // initial decision based on table look-up
    n = m->decoder_table[t+1] + 1;
 
    while (n > sym + 1) {                      // finish with bisection search
      U32 k = (sym + n) >> 1;
      if (m->distribution[k] > dv) n = k; else sym = k;
    }
                                                           // compute products
    x = m->distribution[sym] * length;
    if (sym != m->last_symbol) y = m->distribution[sym+1] * length;
  }
 
  else {                                  // decode using only multiplications
 
    x = sym = 0;
    length >>= DM__LengthShift;
    U32 k = (n = m->symbols) >> 1;
                                                // decode via bisection search
    do {
      U32 z = length * m->distribution[k];
      if (z > value) {
        n = k;
        y = z;                                             // value is smaller
      }
      else {
        sym = k;
        x = z;                                     // value is larger or equal
      }
    } while ((k = (sym + n) >> 1) != sym);
  }
 
  value -= x;                                               // update interval
  length = y - x;
 
  if (length < AC__MinLength) renorm_dec_interval();        // renormalization
 
  ++m->symbol_count[sym];
  if (--m->symbols_until_update == 0) m->update();    // periodic model update
 
  return sym;
}
 
U32 ArithmeticDecoder::readBit()
{
  U32 sym = value / (length >>= 1);            // decode symbol, change length
  value -= length * sym;                                    // update interval
 
  if (length < AC__MinLength) renorm_dec_interval();        // renormalization
 
  return sym;
}
 
U32 ArithmeticDecoder::readBits(U32 bits)
{
  assert(bits && (bits <= 32));
 
  if (bits > 19)
  {
    U32 tmp = readShort();
    bits = bits - 16;
    U32 tmp1 = readBits(bits) << 16;
    return (tmp1|tmp);
  }
 
  U32 sym = value / (length >>= bits);// decode symbol, change length
  value -= length * sym;                                    // update interval
 
  if (length < AC__MinLength) renorm_dec_interval();        // renormalization
 
  return sym;
}
 
U8 ArithmeticDecoder::readByte()
{
  U32 sym = value / (length >>= 8);            // decode symbol, change length
  value -= length * sym;                                    // update interval
 
  if (length < AC__MinLength) renorm_dec_interval();        // renormalization
 
  assert(sym < (1<<8));
 
  return (U8)sym;
}
 
U16 ArithmeticDecoder::readShort()
{
  U32 sym = value / (length >>= 16);           // decode symbol, change length
  value -= length * sym;                                    // update interval
 
  if (length < AC__MinLength) renorm_dec_interval();        // renormalization
 
  assert(sym < (1<<16));
 
  return (U16)sym;
}
 
inline U32 ArithmeticDecoder::readInt()
{
  U32 lowerInt = readShort();
  U32 upperInt = readShort();
  return (upperInt<<16)|lowerInt;
}
 
inline F32 ArithmeticDecoder::readFloat() /* danger in float reinterpretation */
{
  U32I32F32 u32i32f32;
  u32i32f32.u32 = readInt();
  return u32i32f32.f32;
}
 
inline U64 ArithmeticDecoder::readInt64()
{
  U64 lowerInt = readInt();
  U64 upperInt = readInt();
  return (upperInt<<32)|lowerInt;
}
 
inline F64 ArithmeticDecoder::readDouble() /* danger in float reinterpretation */
{
  U64I64F64 u64i64f64;
  u64i64f64.u64 = readInt64();
  return u64i64f64.f64;
}
 
ArithmeticDecoder::~ArithmeticDecoder()
{
 
}
 
inline void ArithmeticDecoder::renorm_dec_interval()
{
  do {                                          // read least-significant byte
    value = (value << 8) | instream->getByte();
  } while ((length <<= 8) < AC__MinLength);        // length multiplied by 256
}