From 66531c75d3bfd8a013acd8bd3c04a131dae2a1a0 Mon Sep 17 00:00:00 2001
From: Michael Niedermayer <michaelni@gmx.at>
Date: Mon, 11 Jun 2012 11:47:59 +0200
Subject: [PATCH] random_seed: rewrite generic code.

The new code is faster and reuses the previous state in case of
multiple calls. For testing the iterations are reduced and several
entropy sources are disabled.
Its based on SHA-1

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
---
 libavutil/random_seed.c | 59 ++++++++++++++++++++++++++---------------
 1 file changed, 38 insertions(+), 21 deletions(-)

diff --git a/libavutil/random_seed.c b/libavutil/random_seed.c
index 6a8666cca6..d56280d838 100644
--- a/libavutil/random_seed.c
+++ b/libavutil/random_seed.c
@@ -22,8 +22,15 @@
 #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"
+
+#ifndef TEST
+#define TEST 0
+#endif
 
 static int read_random(uint32_t *dst, const char *file)
 {
@@ -40,34 +47,44 @@ static int read_random(uint32_t *dst, const char *file)
 
 static uint32_t get_generic_seed(void)
 {
+    uint8_t tmp[av_sha_size];
+    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++) {
+    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 && 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 || TEST && i-last_i > 8)
+                break;
         }
         last_t = t;
     }
-#ifdef AV_READ_TIME
-    random ^= AV_READ_TIME();
-#else
-    random ^= clock();
-#endif
 
-    random += random >> 32;
+    if(TEST)
+        buffer[0] = buffer[1] = 0;
 
-    return random;
+    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)
@@ -81,7 +98,7 @@ uint32_t av_get_random_seed(void)
     return get_generic_seed();
 }
 
-#ifdef TEST
+#if TEST
 #undef printf
 #define N 256
 #include <stdio.h>