av_random() by Ryan Martell rdm4 name-server-seperator martellventures d0t com

Originally committed as revision 7885 to svn://svn.ffmpeg.org/ffmpeg/trunk

1 files changed, 69 insertions, 0 deletions

diff --git a/libavutil/random.h b/libavutil/random.h
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+++ b/libavutil/random.h
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+/*
+ * Mersenne Twister Random Algorithm
+ * Copyright (c) 2006 Ryan Martell.
+ * Based on A C-program for MT19937, with initialization improved 2002/1/26. Coded by
+ * Takuji Nishimura and Makoto Matsumoto.
+ *
+ * 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 AV_RANDOM_H
+#define AV_RANDOM_H
+
+#define AV_RANDOM_N 624
+
+typedef struct {
+    unsigned int mt[AV_RANDOM_N]; ///< the array for the state vector
+    int index; ///< current untempered value we use as the base.
+} AVRandomState;
+
+
+void av_init_random(unsigned int seed, AVRandomState *state); ///< to be inlined, the struct must be visible, so it doesn't make sense to try and keep it opaque with malloc/free like calls
+void av_random_generate_untempered_numbers(AVRandomState *state); ///< Regenerate the untempered numbers (must be done every 624 iterations, or it will loop)
+
+/** generates a random number on [0,0xffffffff]-interval */
+static inline unsigned int av_random(AVRandomState *state)
+{
+    unsigned int y;
+
+    // regenerate the untempered numbers if we should...
+    if (state->index >= AV_RANDOM_N)
+        av_random_generate_untempered_numbers(state);
+
+    // grab one...
+    y = state->mt[state->index++];
+
+    /* Now temper (Mersenne Twister coefficients) The coefficients for MT19937 are.. */
+    y ^= (y >> 11);
+    y ^= (y << 7) & 0x9d2c5680;
+    y ^= (y << 15) & 0xefc60000;
+    y ^= (y >> 18);
+
+    return y;
+}
+
+/** return random in range [0-1] as double */
+static inline double av_random_real1(AVRandomState *state)
+{
+    /* divided by 2^32-1 */
+    return av_random(state) * (1.0 / 4294967296.0);
+}
+
+// only available if DEBUG is defined in the .c file
+void av_benchmark_random(void);
+#endif // AV_RANDOM_H
+