rc4: extend av_rc4_init() doxy

[ffmpeg] / libavutil / lfg.c

diff --git a/libavutil/lfg.c b/libavutil/lfg.c
index 337ee9e41cc7b33fa7718d6525c3f9285a750da2..4221e6228b649047713d19aa4203b835288de787 100644 (file)
--- a/libavutil/lfg.c
+++ b/libavutil/lfg.c
@@ -2,63 +2,99 @@
  * Lagged Fibonacci PRNG
  * Copyright (c) 2008 Michael Niedermayer
  *
- * This file is part of FFmpeg.
+ * This file is part of Libav.
  *
- * FFmpeg is free software; you can redistribute it and/or
+ * 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.
  *
- * FFmpeg is distributed in the hope that it will be useful,
+ * 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 FFmpeg; if not, write to the Free Software
+ * License along with Libav; if not, write to the Free Software
  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
  */
 
 #include <inttypes.h>
+#include <limits.h>
+#include <math.h>
 #include "lfg.h"
 #include "md5.h"
 #include "intreadwrite.h"
+#include "attributes.h"
 
-void av_cold av_lfg_init(AVLFG *c, unsigned int seed){
-    uint8_t tmp[16]={0};
+av_cold void av_lfg_init(AVLFG *c, unsigned int seed)
+{
+    uint8_t tmp[16] = { 0 };
     int i;
 
-    for(i=8; i<64; i+=4){
-        AV_WL32(tmp, seed); tmp[4]=i;
-        av_md5_sum(tmp, tmp,  16);
-        c->state[i  ]= AV_RL32(tmp);
-        c->state[i+1]= AV_RL32(tmp+4);
-        c->state[i+2]= AV_RL32(tmp+8);
-        c->state[i+3]= AV_RL32(tmp+12);
+    for (i = 8; i < 64; i += 4) {
+        AV_WL32(tmp, seed);
+        tmp[4] = i;
+        av_md5_sum(tmp, tmp, 16);
+        c->state[i    ] = AV_RL32(tmp);
+        c->state[i + 1] = AV_RL32(tmp + 4);
+        c->state[i + 2] = AV_RL32(tmp + 8);
+        c->state[i + 3] = AV_RL32(tmp + 12);
     }
-    c->index=0;
+    c->index = 0;
+}
+
+void av_bmg_get(AVLFG *lfg, double out[2])
+{
+    double x1, x2, w;
+
+    do {
+        x1 = 2.0 / UINT_MAX * av_lfg_get(lfg) - 1.0;
+        x2 = 2.0 / UINT_MAX * av_lfg_get(lfg) - 1.0;
+        w  = x1 * x1 + x2 * x2;
+    } while (w >= 1.0);
+
+    w = sqrt((-2.0 * log(w)) / w);
+    out[0] = x1 * w;
+    out[1] = x2 * w;
 }
 
 #ifdef TEST
 #include "log.h"
-#include "common.h"
+#include "timer.h"
 
 int main(void)
 {
-    int x=0;
+    int x = 0;
     int i, j;
     AVLFG state;
 
     av_lfg_init(&state, 0xdeadbeef);
     for (j = 0; j < 10000; j++) {
         START_TIMER
-        for (i = 0; i < 624; i++) {
-//            av_log(NULL,AV_LOG_ERROR, "%X\n", av_lfg_get(&state));
-            x+=av_lfg_get(&state);
-        }
-        STOP_TIMER("624 calls of av_random");
+        for (i = 0; i < 624; i++)
+            x += av_lfg_get(&state);
+        STOP_TIMER("624 calls of av_lfg_get");
     }
     av_log(NULL, AV_LOG_ERROR, "final value:%X\n", x);
+
+    /* BMG usage example */
+    {
+        double mean   = 1000;
+        double stddev = 53;
+
+        av_lfg_init(&state, 42);
+
+        for (i = 0; i < 1000; i += 2) {
+            double bmg_out[2];
+            av_bmg_get(&state, bmg_out);
+            av_log(NULL, AV_LOG_INFO,
+                   "%f\n%f\n",
+                   bmg_out[0] * stddev + mean,
+                   bmg_out[1] * stddev + mean);
+        }
+    }
+
     return 0;
 }
 #endif