Libav
celp_math.c
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1 /*
2  * Various fixed-point math operations
3  *
4  * Copyright (c) 2008 Vladimir Voroshilov
5  *
6  * This file is part of Libav.
7  *
8  * Libav is free software; you can redistribute it and/or
9  * modify it under the terms of the GNU Lesser General Public
10  * License as published by the Free Software Foundation; either
11  * version 2.1 of the License, or (at your option) any later version.
12  *
13  * Libav is distributed in the hope that it will be useful,
14  * but WITHOUT ANY WARRANTY; without even the implied warranty of
15  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
16  * Lesser General Public License for more details.
17  *
18  * You should have received a copy of the GNU Lesser General Public
19  * License along with Libav; if not, write to the Free Software
20  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
21  */
22 
23 #include <inttypes.h>
24 #include <limits.h>
25 #include <assert.h>
26 
27 #include "avcodec.h"
28 #include "celp_math.h"
29 #include "libavutil/common.h"
30 
31 static const uint16_t exp2a[]=
32 {
33  0, 1435, 2901, 4400, 5931, 7496, 9096, 10730,
34  12400, 14106, 15850, 17632, 19454, 21315, 23216, 25160,
35  27146, 29175, 31249, 33368, 35534, 37747, 40009, 42320,
36  44682, 47095, 49562, 52082, 54657, 57289, 59979, 62727,
37 };
38 
39 static const uint16_t exp2b[]=
40 {
41  3, 712, 1424, 2134, 2845, 3557, 4270, 4982,
42  5696, 6409, 7124, 7839, 8554, 9270, 9986, 10704,
43  11421, 12138, 12857, 13576, 14295, 15014, 15734, 16455,
44  17176, 17898, 18620, 19343, 20066, 20790, 21514, 22238,
45 };
46 
47 int ff_exp2(uint16_t power)
48 {
49  unsigned int result= exp2a[power>>10] + 0x10000;
50 
51  assert(power <= 0x7fff);
52 
53  result= (result<<3) + ((result*exp2b[(power>>5)&31])>>17);
54  return result + ((result*(power&31)*89)>>22);
55 }
56 
62 static const uint16_t tab_log2[33] =
63 {
64  4, 1459, 2870, 4240, 5572, 6867, 8127, 9355,
65  10552, 11719, 12858, 13971, 15057, 16120, 17158, 18175,
66  19170, 20145, 21100, 22036, 22954, 23854, 24738, 25605,
67  26457, 27294, 28116, 28924, 29719, 30500, 31269, 32025, 32769,
68 };
69 
70 int ff_log2_q15(uint32_t value)
71 {
72  uint8_t power_int;
73  uint8_t frac_x0;
74  uint16_t frac_dx;
75 
76  // Stripping zeros from beginning
77  power_int = av_log2(value);
78  value <<= (31 - power_int);
79 
80  // b31 is always non-zero now
81  frac_x0 = (value & 0x7c000000) >> 26; // b26-b31 and [32..63] -> [0..31]
82  frac_dx = (value & 0x03fff800) >> 11;
83 
84  value = tab_log2[frac_x0];
85  value += (frac_dx * (tab_log2[frac_x0+1] - tab_log2[frac_x0])) >> 15;
86 
87  return (power_int << 15) + value;
88 }
int ff_exp2(uint16_t power)
fixed-point implementation of exp2(x) in [0; 1] domain.
Definition: celp_math.c:47
static const uint16_t tab_log2[33]
Table used to compute log2(x)
Definition: celp_math.c:62
uint8_t
int ff_log2_q15(uint32_t value)
Calculate log2(x).
Definition: celp_math.c:70
Libavcodec external API header.
static const uint16_t exp2b[]
Definition: celp_math.c:39
#define av_log2
Definition: intmath.h:85
static const uint16_t exp2a[]
Definition: celp_math.c:31