1/*
2 * Copyright (c) 2009 Baptiste Coudurier <baptiste.coudurier@gmail.com>
3 *
4 * This file is part of Libav.
5 *
6 * Libav is free software; you can redistribute it and/or
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 *
11 * Libav is distributed in the hope that it will be useful,
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
17 * License along with Libav; if not, write to the Free Software
18 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
19 */
20
21#include <unistd.h>
22#include <fcntl.h>
23#include <math.h>
24#include <time.h>
25#include "timer.h"
26#include "random_seed.h"
27
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;
35    err = read(fd, dst, sizeof(*dst));
36    close(fd);
37
38    return err;
39}
40
41static uint32_t get_generic_seed(void)
42{
43    clock_t last_t  = 0;
44    int bits        = 0;
45    uint64_t random = 0;
46    unsigned i;
47    float s = 0.000000000001;
48
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);
57                bits++;
58            }
59        }
60        last_t = t;
61    }
62#ifdef AV_READ_TIME
63    random ^= AV_READ_TIME();
64#else
65    random ^= clock();
66#endif
67
68    random += random >> 32;
69
70    return random;
71}
72
73uint32_t av_get_random_seed(void)
74{
75    uint32_t seed;
76
77    if (read_random(&seed, "/dev/urandom") == sizeof(seed))
78        return seed;
79    if (read_random(&seed, "/dev/random")  == sizeof(seed))
80        return seed;
81    return get_generic_seed();
82}
83