random_seed.c

/*
 * Copyright (c) 2009 Baptiste Coudurier <baptiste.coudurier@gmail.com>
 *
 * This file is part of FFmpeg.
 *
 * FFmpeg is free software; you can redistribute it and/or
 * modify it under the terms of the GNU Lesser General Public
 * License as published by the Free Software Foundation; either
 * version 2.1 of the License, or (at your option) any later version.
 *
 * FFmpeg is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 * Lesser General Public License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public
 * License along with FFmpeg; if not, write to the Free Software
 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
 */

#include "config.h"

#if HAVE_UNISTD_H
#include <unistd.h>
#endif
#include <fcntl.h>
#include <math.h>
#include <time.h>
#include <string.h>
#include "avassert.h"
#include "timer.h"
#include "random_seed.h"
#include "sha.h"
#include "intreadwrite.h"

#ifndef TEST
#define TEST 0
#endif

static int read_random(uint32_t *dst, const char *file)
{
#if HAVE_UNISTD_H
    int fd = open(file, O_RDONLY);
    int err = -1;

    if (fd == -1)
        return -1;
    err = read(fd, dst, sizeof(*dst));
    close(fd);

    return err;
#else
    return -1;
#endif
}

static uint32_t get_generic_seed(void)
{
    uint8_t tmp[120];
    struct AVSHA *sha = (void*)tmp;
    clock_t last_t  = 0;
    static uint64_t i = 0;
    static uint32_t buffer[512] = {0};
    unsigned char digest[32];
    uint64_t last_i = i;

    av_assert0(sizeof(tmp) >= av_sha_size);

    if(TEST){
        memset(buffer, 0, sizeof(buffer));
        last_i = i = 0;
    }else{
#ifdef AV_READ_TIME
        buffer[13] ^= AV_READ_TIME();
        buffer[41] ^= AV_READ_TIME()>>32;
#endif
    }

    for (;;) {
        clock_t t = clock();

        if(last_t == t){
            buffer[i&511]++;
        }else{
            buffer[++i&511]+= (t-last_t) % 3294638521U;
            if(last_i && i-last_i > 4 || i-last_i > 64 || TEST && i-last_i > 8)
                break;
        }
        last_t = t;
    }

    if(TEST)
        buffer[0] = buffer[1] = 0;

    av_sha_init(sha, 160);
    av_sha_update(sha, (uint8_t*)buffer, sizeof(buffer));
    av_sha_final(sha, digest);
    return AV_RB32(digest) + AV_RB32(digest+32);
}

uint32_t av_get_random_seed(void)
{
    uint32_t seed;

    if (read_random(&seed, "/dev/urandom") == sizeof(seed))
        return seed;
    if (read_random(&seed, "/dev/random")  == sizeof(seed))
        return seed;
    return get_generic_seed();
}

#if TEST
#undef printf
#define N 256
#include <stdio.h>

int main(void)
{
    int i, j, retry;
    uint32_t seeds[N];

    for (retry=0; retry<3; retry++){
        for (i=0; i<N; i++){
            seeds[i] = av_get_random_seed();
            for (j=0; j<i; j++)
                if (seeds[j] == seeds[i])
                    goto retry;
        }
        printf("seeds OK\n");
        return 0;
        retry:;
    }
    printf("FAIL at %d with %X\n", j, seeds[j]);
    return 1;
}
#endif