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

Originally committed as revision 7885 to svn://svn.ffmpeg.org/ffmpeg/trunk
2025-10-30 23:18:11 +02:00 · 2007-02-08 22:09:05 +00:00
parent a264a081b2
commit fbabf1e0b6
3 changed files with 176 additions and 1 deletions
--- a/libavutil/Makefile
+++ b/libavutil/Makefile
@@ -17,9 +17,11 @@ OBJS= mathematics.o \
      fifo.o \
      tree.o \
      lzo.o \
+      random.o \

 HEADERS = avutil.h common.h mathematics.h integer.h rational.h \
-          intfloat_readwrite.h md5.h adler32.h log.h fifo.h lzo.h
+          intfloat_readwrite.h md5.h adler32.h log.h fifo.h lzo.h \
+          random.h

 NAME=avutil
 ifeq ($(BUILD_SHARED),yes)
--- a/libavutil/random.c
+++ b/libavutil/random.c
@@ -0,0 +1,104 @@
+/*
+ * 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
+ */
+
+
+/**
+see http://en.wikipedia.org/wiki/Mersenne_twister for an explanation of this algorithm.
+*/
+#include <stdio.h>
+#include "random.h"
+
+//#define DEBUG
+
+#ifdef DEBUG
+#include "common.h"
+#include "log.h"
+#endif
+
+
+/* Period parameters */
+#define M 397
+#define A 0x9908b0df /* constant vector a */
+#define UPPER_MASK 0x80000000 /* most significant w-r bits */
+#define LOWER_MASK 0x7fffffff /* least significant r bits */
+
+/** initializes mt[AV_RANDOM_N] with a seed */
+void av_init_random(unsigned int seed, AVRandomState *state)
+{
+    int index;
+
+    /*
+     This differs from the wikipedia article.  Source is from the Makoto
+     Makoto Matsumoto and Takuji Nishimura code, with the following comment:
+     */
+     /* See Knuth TAOCP Vol2. 3rd Ed. P.106 for multiplier. */
+     /* In the previous versions, MSBs of the seed affect   */
+     /* only MSBs of the array mt[].                        */
+    state->mt[0] = seed & 0xffffffff;
+    for (index = 1; index < AV_RANDOM_N; index++) {
+        unsigned int prev= state->mt[index - 1];
+        state->mt[index] = (1812433253UL * (prev ^ (prev>>30)) + index) & 0xffffffff;
+    }
+    state->index= index; // will cause it to generate untempered numbers the first iteration
+}
+
+/** generate AV_RANDOM_N words at one time (which will then be tempered later) (av_random calls this; you shouldn't) */
+void av_random_generate_untempered_numbers(AVRandomState *state)
+{
+    int kk;
+    unsigned int y;
+
+    for (kk = 0; kk < AV_RANDOM_N - M; kk++) {
+        y = (state->mt[kk] & UPPER_MASK) | (state->mt[kk + 1] & LOWER_MASK);
+        state->mt[kk] = state->mt[kk + M] ^ (y >> 1) ^ ((y&1)*A);
+    }
+    for (; kk < AV_RANDOM_N - 1; kk++) {
+        y = (state->mt[kk] & UPPER_MASK) | (state->mt[kk + 1] & LOWER_MASK);
+        state->mt[kk] = state->mt[kk + (M - AV_RANDOM_N)] ^ (y >> 1) ^ ((y&1)*A);
+    }
+    y = (state->mt[AV_RANDOM_N - 1] & UPPER_MASK) | (state->mt[0] & LOWER_MASK);
+    state->mt[AV_RANDOM_N - 1] = state->mt[M - 1] ^ (y >> 1) ^ ((y&1)*A);
+    state->index = 0;
+}
+
+#ifdef DEBUG
+void av_benchmark_random(void)
+{
+    int x=0;
+    int i, j;
+    AVRandomState state;
+
+    av_init_random(0xdeadbeef, &state);
+    for (j = 0; j < 100; j++) {
+        START_TIMER;
+        x+= av_random(&state);
+        STOP_TIMER("first call to av_random");
+        for (i = 1; i < AV_RANDOM_N; i++) {
+            START_TIMER;
+            x+= av_random(&state);
+            STOP_TIMER("AV_RANDOM_N calls of av_random");
+        }
+    }
+    av_log(NULL, AV_LOG_ERROR, "final value:%X\n", x);
+}
+#endif
--- a/libavutil/random.h
+++ b/libavutil/random.h
@@ -0,0 +1,69 @@
+/*
+ * 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
+