1/* Copyright (c) 2007 CSIRO
2   Copyright (c) 2007-2009 Xiph.Org Foundation
3   Written by Jean-Marc Valin */
4/*
5   Redistribution and use in source and binary forms, with or without
6   modification, are permitted provided that the following conditions
7   are met:
8
9   - Redistributions of source code must retain the above copyright
10   notice, this list of conditions and the following disclaimer.
11
12   - Redistributions in binary form must reproduce the above copyright
13   notice, this list of conditions and the following disclaimer in the
14   documentation and/or other materials provided with the distribution.
15
16   THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
17   ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
18   LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
19   A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER
20   OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
21   EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
22   PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
23   PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
24   LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
25   NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
26   SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
27*/
28
29#ifdef HAVE_CONFIG_H
30#include "config.h"
31#endif
32
33#include "laplace.h"
34#include "mathops.h"
35
36/* The minimum probability of an energy delta (out of 32768). */
37#define LAPLACE_LOG_MINP (0)
38#define LAPLACE_MINP (1<<LAPLACE_LOG_MINP)
39/* The minimum number of guaranteed representable energy deltas (in one
40    direction). */
41#define LAPLACE_NMIN (16)
42
43/* When called, decay is positive and at most 11456. */
44static unsigned ec_laplace_get_freq1(unsigned fs0, int decay)
45{
46   unsigned ft;
47   ft = 32768 - LAPLACE_MINP*(2*LAPLACE_NMIN) - fs0;
48   return ft*(opus_int32)(16384-decay)>>15;
49}
50
51void ec_laplace_encode(ec_enc *enc, int *value, unsigned fs, int decay)
52{
53   unsigned fl;
54   int val = *value;
55   fl = 0;
56   if (val)
57   {
58      int s;
59      int i;
60      s = -(val<0);
61      val = (val+s)^s;
62      fl = fs;
63      fs = ec_laplace_get_freq1(fs, decay);
64      /* Search the decaying part of the PDF.*/
65      for (i=1; fs > 0 && i < val; i++)
66      {
67         fs *= 2;
68         fl += fs+2*LAPLACE_MINP;
69         fs = (fs*(opus_int32)decay)>>15;
70      }
71      /* Everything beyond that has probability LAPLACE_MINP. */
72      if (!fs)
73      {
74         int di;
75         int ndi_max;
76         ndi_max = (32768-fl+LAPLACE_MINP-1)>>LAPLACE_LOG_MINP;
77         ndi_max = (ndi_max-s)>>1;
78         di = IMIN(val - i, ndi_max - 1);
79         fl += (2*di+1+s)*LAPLACE_MINP;
80         fs = IMIN(LAPLACE_MINP, 32768-fl);
81         *value = (i+di+s)^s;
82      }
83      else
84      {
85         fs += LAPLACE_MINP;
86         fl += fs&~s;
87      }
88      celt_assert(fl+fs<=32768);
89      celt_assert(fs>0);
90   }
91   ec_encode_bin(enc, fl, fl+fs, 15);
92}
93
94int ec_laplace_decode(ec_dec *dec, unsigned fs, int decay)
95{
96   int val=0;
97   unsigned fl;
98   unsigned fm;
99   fm = ec_decode_bin(dec, 15);
100   fl = 0;
101   if (fm >= fs)
102   {
103      val++;
104      fl = fs;
105      fs = ec_laplace_get_freq1(fs, decay)+LAPLACE_MINP;
106      /* Search the decaying part of the PDF.*/
107      while(fs > LAPLACE_MINP && fm >= fl+2*fs)
108      {
109         fs *= 2;
110         fl += fs;
111         fs = ((fs-2*LAPLACE_MINP)*(opus_int32)decay)>>15;
112         fs += LAPLACE_MINP;
113         val++;
114      }
115      /* Everything beyond that has probability LAPLACE_MINP. */
116      if (fs <= LAPLACE_MINP)
117      {
118         int di;
119         di = (fm-fl)>>(LAPLACE_LOG_MINP+1);
120         val += di;
121         fl += 2*di*LAPLACE_MINP;
122      }
123      if (fm < fl+fs)
124         val = -val;
125      else
126         fl += fs;
127   }
128   celt_assert(fl<32768);
129   celt_assert(fs>0);
130   celt_assert(fl<=fm);
131   celt_assert(fm<IMIN(fl+fs,32768));
132   ec_dec_update(dec, fl, IMIN(fl+fs,32768), 32768);
133   return val;
134}
135