From: Michael Niedermayer <[email protected]>
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 built with MSVC finish in finite time
when run in wine. (The one built with mingw actually manages to find
/dev/urandom so it doesn't do the generic code, but the MSVC build
doesn't try to do this.) On real windows, it seems to finish pretty
quickly.
---
libavutil/random_seed.c | 50 +++++++++++++++++++++++++++--------------------
1 file changed, 29 insertions(+), 21 deletions(-)
diff --git a/libavutil/random_seed.c b/libavutil/random_seed.c
index 8ee4cb7..a312600 100644
--- a/libavutil/random_seed.c
+++ b/libavutil/random_seed.c
@@ -26,8 +26,12 @@
#include <fcntl.h>
#include <math.h>
#include <time.h>
+#include <string.h>
#include "timer.h"
#include "random_seed.h"
+#include "sha.h"
+#include "intreadwrite.h"
+#include <assert.h>
static int read_random(uint32_t *dst, const char *file)
{
@@ -48,34 +52,38 @@ static int read_random(uint32_t *dst, const char *file)
static uint32_t get_generic_seed(void)
{
+ uint8_t tmp[120];
+ struct AVSHA *sha = (void*)tmp;
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[32];
+ uint64_t last_i = i;
- for (i = 0; bits < 64; i++) {
+ assert(sizeof(tmp) >= av_sha_size);
+
+#ifdef AV_READ_TIME
+ buffer[13] ^= AV_READ_TIME();
+ buffer[41] ^= AV_READ_TIME() >> 32;
+#endif
+
+ 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;
+ av_sha_init(sha, 160);
+ av_sha_update(sha, buffer, sizeof(buffer));
+ av_sha_final(sha, digest);
+ return AV_RB32(digest) + AV_RB32(digest + 32);
}
uint32_t av_get_random_seed(void)
--
1.7.9.5
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