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

1 files changed, 37 insertions, 0 deletions

diff --git a/libavutil/lfg.h b/libavutil/lfg.h
new file mode 100644
index 0000000000..0882faab02
--- /dev/null
+++ b/libavutil/lfg.h
@@ -0,0 +1,37 @@
+/*
+ * 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