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/* (C) 2007 Jean-Marc Valin, CSIRO
*/
/*
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
LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
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"
static int ec_laplace_get_total(int decay)
{
return (1<<30)/((1<<14) - decay) - (1<<15) + 1;
}
void ec_laplace_encode(ec_enc *enc, int value, int decay)
{
int i, fl, fs, ft;
int s = 0;
if (value < 0)
{
s = 1;
value = -value;
}
ft = ec_laplace_get_total(decay);
fl = -(1<<15);
fs = 1<<15;
for (i=0;i<value;i++)
{
int tmp_l, tmp_s;
tmp_l = fl;
tmp_s = fs;
fl += fs*2;
fs = (fs*decay)>>14;
if (fs == 0)
{
fs = tmp_s;
fl = tmp_l;
break;
}
}
if (fl < 0)
fl = 0;
if (s)
fl += fs;
/*printf ("enc: %d %d %d\n", fl, fs, ft);*/
ec_encode(enc, fl, fl+fs, ft);
}
int ec_laplace_decode(ec_dec *dec, int decay)
{
int val=0;
int fl, fh, fs, ft, fm;
ft = ec_laplace_get_total(decay);
fm = ec_decode(dec, ft);
/*printf ("fm: %d/%d\n", fm, ft);*/
fl = 0;
fs = 1<<15;
fh = fs;
while (fm >= fh && fs != 0)
{
fl = fh;
fs = (fs*decay)>>14;
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;
}
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