ee7154265246126c2998326f5e3e30599ae643ba
[libav.git] / libavutil / random_seed.c
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
28 static 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
41 static 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
73 uint32_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 }