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