libavutil/random_seed.c

   1 /*
   2  * Copyright (c) 2009 Baptiste Coudurier <baptiste.coudurier@gmail.com>
   3  *
   4  * This file is part of FFmpeg.
   5  *
   6  * FFmpeg 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  * FFmpeg 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 FFmpeg; 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 "timer.h"
  24 #include "time.h"
  25 #include "random_seed.h"
  26 #include "avutil.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     int last_t=0;
  44     int bits=0;
  45     uint64_t random=0;
  46     unsigned i;
  47     int s=0;
  48
  49     for(i=0;bits<64;i++){
  50         int t= clock()>>s;
  51         if(last_t && t != last_t){
  52             if(i<10000 && s<24){
  53                 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 }
  83
  84 #if LIBAVUTIL_VERSION_MAJOR < 51
  85 attribute_deprecated uint32_t ff_random_get_seed(void);
  86 uint32_t ff_random_get_seed(void)
  87 {
  88     return av_get_random_seed();
  89 }
  90 #endif