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2ba45a60 DM |
1 | /* |
2 | * Lagged Fibonacci PRNG | |
3 | * Copyright (c) 2008 Michael Niedermayer | |
4 | * | |
5 | * This file is part of FFmpeg. | |
6 | * | |
7 | * FFmpeg is free software; you can redistribute it and/or | |
8 | * modify it under the terms of the GNU Lesser General Public | |
9 | * License as published by the Free Software Foundation; either | |
10 | * version 2.1 of the License, or (at your option) any later version. | |
11 | * | |
12 | * FFmpeg is distributed in the hope that it will be useful, | |
13 | * but WITHOUT ANY WARRANTY; without even the implied warranty of | |
14 | * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU | |
15 | * Lesser General Public License for more details. | |
16 | * | |
17 | * You should have received a copy of the GNU Lesser General Public | |
18 | * License along with FFmpeg; if not, write to the Free Software | |
19 | * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA | |
20 | */ | |
21 | ||
22 | #include <inttypes.h> | |
23 | #include <limits.h> | |
24 | #include <math.h> | |
25 | #include "lfg.h" | |
26 | #include "md5.h" | |
27 | #include "intreadwrite.h" | |
28 | #include "attributes.h" | |
29 | ||
30 | av_cold void av_lfg_init(AVLFG *c, unsigned int seed) | |
31 | { | |
32 | uint8_t tmp[16] = { 0 }; | |
33 | int i; | |
34 | ||
35 | for (i = 8; i < 64; i += 4) { | |
36 | AV_WL32(tmp, seed); | |
37 | tmp[4] = i; | |
38 | av_md5_sum(tmp, tmp, 16); | |
39 | c->state[i ] = AV_RL32(tmp); | |
40 | c->state[i + 1] = AV_RL32(tmp + 4); | |
41 | c->state[i + 2] = AV_RL32(tmp + 8); | |
42 | c->state[i + 3] = AV_RL32(tmp + 12); | |
43 | } | |
44 | c->index = 0; | |
45 | } | |
46 | ||
47 | void av_bmg_get(AVLFG *lfg, double out[2]) | |
48 | { | |
49 | double x1, x2, w; | |
50 | ||
51 | do { | |
52 | x1 = 2.0 / UINT_MAX * av_lfg_get(lfg) - 1.0; | |
53 | x2 = 2.0 / UINT_MAX * av_lfg_get(lfg) - 1.0; | |
54 | w = x1 * x1 + x2 * x2; | |
55 | } while (w >= 1.0); | |
56 | ||
57 | w = sqrt((-2.0 * log(w)) / w); | |
58 | out[0] = x1 * w; | |
59 | out[1] = x2 * w; | |
60 | } | |
61 | ||
62 | #ifdef TEST | |
63 | #include "log.h" | |
64 | #include "timer.h" | |
65 | ||
66 | int main(void) | |
67 | { | |
68 | int x = 0; | |
69 | int i, j; | |
70 | AVLFG state; | |
71 | ||
72 | av_lfg_init(&state, 0xdeadbeef); | |
73 | for (j = 0; j < 10000; j++) { | |
74 | START_TIMER | |
75 | for (i = 0; i < 624; i++) { | |
76 | //av_log(NULL, AV_LOG_ERROR, "%X\n", av_lfg_get(&state)); | |
77 | x += av_lfg_get(&state); | |
78 | } | |
79 | STOP_TIMER("624 calls of av_lfg_get"); | |
80 | } | |
81 | av_log(NULL, AV_LOG_ERROR, "final value:%X\n", x); | |
82 | ||
83 | /* BMG usage example */ | |
84 | { | |
85 | double mean = 1000; | |
86 | double stddev = 53; | |
87 | ||
88 | av_lfg_init(&state, 42); | |
89 | ||
90 | for (i = 0; i < 1000; i += 2) { | |
91 | double bmg_out[2]; | |
92 | av_bmg_get(&state, bmg_out); | |
93 | av_log(NULL, AV_LOG_INFO, | |
94 | "%f\n%f\n", | |
95 | bmg_out[0] * stddev + mean, | |
96 | bmg_out[1] * stddev + mean); | |
97 | } | |
98 | } | |
99 | ||
100 | return 0; | |
101 | } | |
102 | #endif |