libcelt/laplace.c

/* Copyright (c) 2007 CSIRO
   Copyright (c) 2007-2009 Xiph.Org Foundation
   Written by Jean-Marc Valin */
/*
   Redistribution and use in source and binary forms, with or without
   modification, are permitted provided that the following conditions
   are met:
   
   - Redistributions of source code must retain the above copyright
   notice, this list of conditions and the following disclaimer.
   
   - Redistributions in binary form must reproduce the above copyright
   notice, this list of conditions and the following disclaimer in the
   documentation and/or other materials provided with the distribution.
   
   - Neither the name of the Xiph.org Foundation nor the names of its
   contributors may be used to endorse or promote products derived from
   this software without specific prior written permission.
   
   THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
   ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
   LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
   A PARTICULAR PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE FOUNDATION OR
   CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
   EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
   PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
   PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
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   NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
   SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
*/

#ifdef HAVE_CONFIG_H
#include "config.h"
#endif

#include "laplace.h"
#include "mathops.h"

/* The minimum probability of an energy delta (out of 32768). */
#define LAPLACE_LOG_MINP (0)
#define LAPLACE_MINP (1<<LAPLACE_LOG_MINP)
/* The minimum number of guaranteed representable energy deltas (in one
    direction). */
#define LAPLACE_NMIN (16)

int ec_laplace_get_start_freq(int decay)
{
   celt_uint32 ft = 32768 - LAPLACE_MINP*(2*LAPLACE_NMIN+1);
   int fs = (ft*(16384-decay))/(16384+decay);
   return fs+LAPLACE_MINP;
}

static int ec_laplace_get_freq1(int fs0, int decay)
{
   celt_int32 ft;
   ft = 32768 - LAPLACE_MINP*(2*LAPLACE_NMIN) - fs0;
   return ft*(16384-decay)>>15;
}

void ec_laplace_encode_start(ec_enc *enc, int *value, int decay, int fs)
{
   unsigned fl;
   int val = *value;
   fl = 0;
   if (val)
   {
      int s;
      int i;
      s = -(val<0);
      val = val+s^s;
      fl = fs;
      fs = ec_laplace_get_freq1(fs, decay);
      /* Search the decaying part of the PDF.*/
      for (i=1; fs > 0 && i < val; i++)
      {
         fs *= 2;
         fl += fs+2*LAPLACE_MINP;
         fs = (fs*(celt_int32)decay)>>15;
      }
      /* Everything beyond that has probability LAPLACE_MINP. */
      if (fs <= 0)
      {
         int di;
         int di_max;
         di_max = (32768-fl+LAPLACE_MINP-1)>>LAPLACE_LOG_MINP;
         di_max = (di_max-s)>>1;
         di = IMIN(val - i, di_max);
         fl += (2*di+1+s)*LAPLACE_MINP;
         fs = IMIN(LAPLACE_MINP, 32768-fl);
         *value = i+di+s^s;
      }
      else
      {
         fs += LAPLACE_MINP;
         fl += fs&~s;
      }
      celt_assert(fl+fs<=32768);
      celt_assert(fs>0);
   }
   ec_encode_bin(enc, fl, fl+fs, 15);
}


void ec_laplace_encode(ec_enc *enc, int *value, int decay)
{
   int fs = ec_laplace_get_start_freq(decay);
   ec_laplace_encode_start(enc, value, decay, fs);
}


int ec_laplace_decode_start(ec_dec *dec, int decay, int fs)
{
   int val=0;
   unsigned fl;
   int fm;
   fm = ec_decode_bin(dec, 15);
   fl = 0;
   if (fm >= fs)
   {
      val++;
      fl = fs;
      fs = ec_laplace_get_freq1(fs, decay)+LAPLACE_MINP;
      /* Search the decaying part of the PDF.*/
      while(fs > LAPLACE_MINP && fm >= fl+2*fs)
      {
         fs *= 2;
         fl += fs;
         fs = ((fs-2*LAPLACE_MINP)*(celt_int32)decay)>>15;
         fs += LAPLACE_MINP;
         val++;
      }
      /* Everything beyond that has probability LAPLACE_MINP. */
      if (fs <= LAPLACE_MINP)
      {
         int di;
         di = (fm-fl)>>(LAPLACE_LOG_MINP+1);
         val += di;
         fl += 2*di*LAPLACE_MINP;
      }
      if (fm < fl+fs)
         val = -val;
      else
         fl += fs;
   }
   celt_assert(fl<32768);
   celt_assert(fs>0);
   celt_assert(fl<=fm);
   celt_assert(fm<IMIN(fl+fs,32768));
   ec_dec_update(dec, fl, IMIN(fl+fs,32768), 32768);
   return val;
}

int ec_laplace_decode(ec_dec *dec, int decay)
{
   int fs = ec_laplace_get_start_freq(decay);
   return ec_laplace_decode_start(dec, decay, fs);
}