FFmpeg/libavutil/random_seed.c
Michael Niedermayer 01d245ef43 random_seed: Rewrite the generic clock() based seed code
The new code is faster and reuses the previous state in case of
multiple calls.

The previous code could easily end up in near-infinite loops,
if the difference between two clock() calls never was larger than
1.

This makes fate-parseutils finish in finite time when run in wine,
if CryptGenRandom isn't available (which e.g. isn't available if
targeting Windows RT/metro).

Patch originally by Michael Niedermayer but with some modifications
by Martin Storsjö.

Signed-off-by: Martin Storsjö <martin@martin.st>
2014-01-06 18:53:58 +02:00

116 lines
3.0 KiB
C

/*
* Copyright (c) 2009 Baptiste Coudurier <baptiste.coudurier@gmail.com>
*
* This file is part of Libav.
*
* Libav 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.
*
* Libav 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 Libav; 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
#if HAVE_CRYPTGENRANDOM
#include <windows.h>
#include <wincrypt.h>
#endif
#include <fcntl.h>
#include <math.h>
#include <time.h>
#include "internal.h"
#include "intreadwrite.h"
#include "mem.h"
#include "timer.h"
#include "random_seed.h"
#include "sha.h"
static int read_random(uint32_t *dst, const char *file)
{
#if HAVE_UNISTD_H
int fd = avpriv_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)
{
struct AVSHA *sha = av_sha_alloc();
clock_t last_t = 0;
static uint64_t i = 0;
static uint32_t buffer[512] = { 0 };
unsigned char digest[20];
uint64_t last_i = i;
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)
break;
}
last_t = t;
}
if (!sha) {
uint32_t seed = 0;
int j;
// Unable to allocate an sha context, just xor the buffer together
// to create something hopefully unique.
for (j = 0; j < 512; j++)
seed ^= buffer[j];
return seed;
}
av_sha_init(sha, 160);
av_sha_update(sha, (const uint8_t *) buffer, sizeof(buffer));
av_sha_final(sha, digest);
av_free(sha);
return AV_RB32(digest) + AV_RB32(digest + 16);
}
uint32_t av_get_random_seed(void)
{
uint32_t seed;
#if HAVE_CRYPTGENRANDOM
HCRYPTPROV provider;
if (CryptAcquireContext(&provider, NULL, NULL, PROV_RSA_FULL,
CRYPT_VERIFYCONTEXT | CRYPT_SILENT)) {
BOOL ret = CryptGenRandom(provider, sizeof(seed), (PBYTE) &seed);
CryptReleaseContext(provider, 0);
if (ret)
return seed;
}
#endif
if (read_random(&seed, "/dev/urandom") == sizeof(seed))
return seed;
if (read_random(&seed, "/dev/random") == sizeof(seed))
return seed;
return get_generic_seed();
}