a9ebef697c4b8f3ea2799414b0dffc23345b33c9
[libav.git] / libavcodec / celp_math.c
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
57 /**
58 * Table used to compute log2(x)
59 *
60 * tab_log2[i] = (1<<15) * log2(1 + i/32), i=0..32
61 */
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 }