Code clean-up for crc.c, lfg.c, log.c, random_see.d, rational.c and tree.c.
[libav.git] / libavutil / random_seed.c
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1/*
2 * Copyright (c) 2009 Baptiste Coudurier <baptiste.coudurier@gmail.com>
3 *
2912e87a 4 * This file is part of Libav.
48d58e59 5 *
2912e87a 6 * Libav is free software; you can redistribute it and/or
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7 * modify it under the terms of the GNU Lesser General Public
8 * License as published by the Free Software Foundation; either
9 * version 2.1 of the License, or (at your option) any later version.
10 *
2912e87a 11 * Libav is distributed in the hope that it will be useful,
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12 * but WITHOUT ANY WARRANTY; without even the implied warranty of
13 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
14 * Lesser General Public License for more details.
15 *
16 * You should have received a copy of the GNU Lesser General Public
2912e87a 17 * License along with Libav; if not, write to the Free Software
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18 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
19 */
20
21#include <unistd.h>
22#include <fcntl.h>
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23#include <math.h>
24#include <time.h>
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25#include "timer.h"
26#include "random_seed.h"
27
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28static int read_random(uint32_t *dst, const char *file)
29{
30 int fd = open(file, O_RDONLY);
31 int err = -1;
32
33 if (fd == -1)
34 return -1;
9958096e 35 err = read(fd, dst, sizeof(*dst));
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36 close(fd);
37
38 return err;
39}
40
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41static uint32_t get_generic_seed(void)
42{
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43 clock_t last_t = 0;
44 int bits = 0;
45 uint64_t random = 0;
b65c1ccf 46 unsigned i;
425b45d4 47 float s = 0.000000000001;
c84d5aa7 48
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49 for (i = 0; bits < 64; i++) {
50 clock_t t = clock();
51 if (last_t && fabs(t - last_t) > s || t == (clock_t) -1) {
52 if (i < 10000 && s < (1 << 24)) {
53 s += s;
54 i = t = 0;
55 } else {
56 random = 2 * random + (i & 1);
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57 bits++;
58 }
59 }
425b45d4 60 last_t = t;
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61 }
62#ifdef AV_READ_TIME
63 random ^= AV_READ_TIME();
64#else
65 random ^= clock();
66#endif
67
425b45d4 68 random += random >> 32;
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69
70 return random;
71}
72
576fb48e 73uint32_t av_get_random_seed(void)
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74{
75 uint32_t seed;
38e23c88 76
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77 if (read_random(&seed, "/dev/urandom") == sizeof(seed))
78 return seed;
79 if (read_random(&seed, "/dev/random") == sizeof(seed))
38e23c88 80 return seed;
c84d5aa7 81 return get_generic_seed();
48d58e59 82}