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ffmpeg / libavutil / random_seed.c @ 5d6e4c16

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1 48d58e59 Baptiste Coudurier
/*
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 * Copyright (c) 2009 Baptiste Coudurier <baptiste.coudurier@gmail.com>
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 *
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 * This file is part of FFmpeg.
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 *
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 * FFmpeg is free software; you can redistribute it and/or
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 * modify it under the terms of the GNU Lesser General Public
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 * License as published by the Free Software Foundation; either
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 * version 2.1 of the License, or (at your option) any later version.
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 *
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 * FFmpeg is distributed in the hope that it will be useful,
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 * but WITHOUT ANY WARRANTY; without even the implied warranty of
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 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
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 * Lesser General Public License for more details.
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 *
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 * You should have received a copy of the GNU Lesser General Public
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 * License along with FFmpeg; if not, write to the Free Software
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 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
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 */
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#include <unistd.h>
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#include <fcntl.h>
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#include "timer.h"
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#include "time.h"
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#include "random_seed.h"
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#include "avutil.h"
27 48d58e59 Baptiste Coudurier
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static int read_random(uint32_t *dst, const char *file)
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{
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    int fd = open(file, O_RDONLY);
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    int err = -1;
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    if (fd == -1)
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        return -1;
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    err = read(fd, dst, sizeof(*dst));
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    close(fd);
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    return err;
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}
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static uint32_t get_generic_seed(void)
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{
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    clock_t last_t=0;
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    int bits=0;
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    uint64_t random=0;
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    unsigned i;
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    float s=0.000000000001;
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    for(i=0;bits<64;i++){
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        clock_t t= clock();
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        if(last_t && fabs(t-last_t)>s || t==(clock_t)-1){
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            if(i<10000 && s<(1<<24)){
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                s+=s;
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                i=t=0;
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            }else{
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                random= 2*random + (i&1);
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                bits++;
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            }
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        }
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        last_t= t;
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    }
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#ifdef AV_READ_TIME
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    random ^= AV_READ_TIME();
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#else
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    random ^= clock();
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#endif
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    random += random>>32;
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    return random;
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}
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uint32_t av_get_random_seed(void)
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{
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    uint32_t seed;
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    if (read_random(&seed, "/dev/urandom") == sizeof(seed))
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        return seed;
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    if (read_random(&seed, "/dev/random")  == sizeof(seed))
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        return seed;
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    return get_generic_seed();
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}
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#if LIBAVUTIL_VERSION_MAJOR < 51
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attribute_deprecated uint32_t ff_random_get_seed(void);
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uint32_t ff_random_get_seed(void)
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{
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    return av_get_random_seed();
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}
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#endif