Simple lagged fibonacci PRNG.

3.5 times faster than our mersene twister.
10 times less memory needed. (=less cache trashing)

Originally committed as revision 14458 to svn://svn.ffmpeg.org/ffmpeg/trunk

libavutil/lfg.c

+/*
+ * Lagged Fibonacci PRNG
+ * Copyright (c) 2008 Michael Niedermayer
+ *
+ * This file is part of FFmpeg.
+ *
+ * FFmpeg 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,
+ * 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
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
+ */
+
+#include <inttypes.h>
+#include "lfg.h"
+#include "md5.h"
+#include "intreadwrite.h"
+
+void av_cold 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);
+    }
+    c->index=0;
+}
+
+#ifdef TEST
+#include "log.h"
+#include "common.h"
+
+int main(void)
+{
+    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");
+    }
+    av_log(NULL, AV_LOG_ERROR, "final value:%X\n", x);
+    return 0;
+}
+#endif

libavutil/lfg.h

+/*
+ * Lagged Fibonacci PRNG
+ * Copyright (c) 2008 Michael Niedermayer
+ *
+ * This file is part of FFmpeg.
+ *
+ * FFmpeg 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,
+ * 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
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
+ */
+
+#ifndef FFMPEG_LFG_H
+#define FFMPEG_LFG_H
+
+typedef struct {
+    unsigned int state[64];
+    int index;
+} AVLFG;
+
+void av_lfg_init(AVLFG *c, unsigned int seed);
+
+static inline unsigned int av_lfg_get(AVLFG *c){
+    c->state[c->index & 63] = c->state[(c->index-24) & 63] + c->state[(c->index-55) & 63];
+    return c->state[c->index++ & 63];
+}
+
+#endif //FFMPEG_LFG_H