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authorMichael Niedermayer <michaelni@gmx.at>2012-06-11 11:47:59 +0200
committerMartin Storsjö <martin@martin.st>2014-01-06 18:53:58 +0200
commit01d245ef4392152dbdc78a6ba4dfa0a6e8b08e6f (patch)
tree9e6b7bf0a2f303f6de689e380b98a9319c917201 /libavutil
parente61b8fa5605b16a02a2a0ea75afbfc31d7832bba (diff)
downloadffmpeg-streaming-01d245ef4392152dbdc78a6ba4dfa0a6e8b08e6f.zip
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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>
Diffstat (limited to 'libavutil')
-rw-r--r--libavutil/random_seed.c51
1 files changed, 30 insertions, 21 deletions
diff --git a/libavutil/random_seed.c b/libavutil/random_seed.c
index 4680081..26884cb 100644
--- a/libavutil/random_seed.c
+++ b/libavutil/random_seed.c
@@ -31,8 +31,11 @@
#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)
{
@@ -53,34 +56,40 @@ static int read_random(uint32_t *dst, const char *file)
static uint32_t get_generic_seed(void)
{
+ struct AVSHA *sha = av_sha_alloc();
clock_t last_t = 0;
- int bits = 0;
- uint64_t random = 0;
- unsigned i;
- float s = 0.000000000001;
+ static uint64_t i = 0;
+ static uint32_t buffer[512] = { 0 };
+ unsigned char digest[20];
+ uint64_t last_i = i;
- for (i = 0; bits < 64; i++) {
+ for (;;) {
clock_t t = clock();
- if (last_t && fabs(t - last_t) > s || t == (clock_t) -1) {
- if (i < 10000 && s < (1 << 24)) {
- s += s;
- i = t = 0;
- } else {
- random = 2 * random + (i & 1);
- bits++;
- }
+
+ 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;
}
-#ifdef AV_READ_TIME
- random ^= AV_READ_TIME();
-#else
- random ^= clock();
-#endif
- random += random >> 32;
-
- return random;
+ 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)
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