cog/Frameworks/libcelt_0061/celt-0.6.1/libcelt/laplace.c

/* (C) 2007 Jean-Marc Valin, CSIRO
*/
/*
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   are met:
   
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   notice, this list of conditions and the following disclaimer.
   
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   notice, this list of conditions and the following disclaimer in the
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   - 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
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   SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
*/

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

#include "laplace.h"

int ec_laplace_get_start_freq(int decay)
{
   int fs = (((ec_uint32)32768)*(16384-decay))/(16384+decay);
   /* Making fs even so we're sure that all the range is used for +/- values */
   fs -= (fs&1);
   return fs;
}

void ec_laplace_encode_start(ec_enc *enc, int *value, int decay, int fs)
{
   int i;
   int fl;
   unsigned int ft;
   int s = 0;
   int val = *value;
   if (val < 0)
   {
      s = 1;
      val = -val;
   }
   ft = 32768;
   fl = -fs;
   for (i=0;i<val;i++)
   {
      int tmp_l, tmp_s;
      tmp_l = fl;
      tmp_s = fs;
      fl += fs*2;
      fs = (fs*(ec_int32)decay)>>14;
      if (fs == 0)
      {
         if (fl+2 <= ft)
         {
            fs = 1;
         } else {
            fs = tmp_s;
            fl = tmp_l;
            if (s)
               *value = -i;
            else
               *value = i;
            break;
         }
      }
   }
   if (fl < 0)
      fl = 0;
   if (s)
      fl += fs;
   ec_encode(enc, fl, fl+fs, ft);
}

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;
   int fl, fh, fm;
   unsigned int ft;
   fl = 0;
   ft = 32768;
   fh = fs;
   fm = ec_decode(dec, ft);
   while (fm >= fh && fs != 0)
   {
      fl = fh;
      fs = (fs*(ec_int32)decay)>>14;
      if (fs == 0 && fh+2 <= ft)
      {
         fs = 1;
      }
      fh += fs*2;
      val++;
   }
   if (fl>0)
   {
      if (fm >= fl+fs)
      {
         val = -val;
         fl += fs;
      } else {
         fh -= fs;
      }
   }
   /* Preventing an infinite loop in case something screws up in the decoding */
   if (fl==fh)
      fl--;
   ec_dec_update(dec, fl, fh, ft);
   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);
}