1/*
2 * Mersenne Twister PRNG algorithm
3 * Copyright (c) 2006 Ryan Martell
4 * Based on a C program for MT19937, with initialization improved 2002/1/26.
5 * Coded by Takuji Nishimura and Makoto Matsumoto.
6 *
7 * This file is part of FFmpeg.
8 *
9 * FFmpeg is free software; you can redistribute it and/or
10 * modify it under the terms of the GNU Lesser General Public
11 * License as published by the Free Software Foundation; either
12 * version 2.1 of the License, or (at your option) any later version.
13 *
14 * FFmpeg is distributed in the hope that it will be useful,
15 * but WITHOUT ANY WARRANTY; without even the implied warranty of
16 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
17 * Lesser General Public License for more details.
18 *
19 * You should have received a copy of the GNU Lesser General Public
20 * License along with FFmpeg; if not, write to the Free Software
21 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
22 */
23
24
25/**
26 * See http://en.wikipedia.org/wiki/Mersenne_twister
27 * for an explanation of this algorithm.
28 */
29#include <stdio.h>
30#include "random.h"
31
32
33/* period parameters */
34#define M 397
35#define A 0x9908b0df /* constant vector a */
36#define UPPER_MASK 0x80000000 /* most significant w-r bits */
37#define LOWER_MASK 0x7fffffff /* least significant r bits */
38
39/** Initializes mt[AV_RANDOM_N] with a seed. */
40void av_random_init(AVRandomState *state, unsigned int seed)
41{
42    int index;
43
44    /*
45     This differs from the Wikipedia article.  Source is from the
46     Makoto Matsumoto and Takuji Nishimura code, with the following comment:
47     */
48     /* See Knuth TAOCP Vol2. 3rd Ed. P.106 for multiplier. */
49     /* In the previous versions, MSBs of the seed affect   */
50     /* only MSBs of the array mt[].                        */
51    state->mt[0] = seed & 0xffffffff;
52    for (index = 1; index < AV_RANDOM_N; index++) {
53        unsigned int prev= state->mt[index - 1];
54        state->mt[index] = (1812433253UL * (prev ^ (prev>>30)) + index) & 0xffffffff;
55    }
56    state->index= index; // Will cause it to generate untempered numbers in the first iteration.
57}
58
59#if LIBAVUTIL_VERSION_MAJOR < 50
60void av_init_random(unsigned int seed, AVRandomState *state)
61{
62    av_random_init(state, seed);
63}
64#endif
65
66/** Generates AV_RANDOM_N words at one time (which will then be tempered later).
67 * av_random calls this; you shouldn't. */
68void av_random_generate_untempered_numbers(AVRandomState *state)
69{
70    int kk;
71    unsigned int y;
72
73    for (kk = 0; kk < AV_RANDOM_N - M; kk++) {
74        y = (state->mt[kk] & UPPER_MASK) | (state->mt[kk + 1] & LOWER_MASK);
75        state->mt[kk] = state->mt[kk + M] ^ (y >> 1) ^ ((y&1)*A);
76    }
77    for (; kk < AV_RANDOM_N - 1; kk++) {
78        y = (state->mt[kk] & UPPER_MASK) | (state->mt[kk + 1] & LOWER_MASK);
79        state->mt[kk] = state->mt[kk + (M - AV_RANDOM_N)] ^ (y >> 1) ^ ((y&1)*A);
80    }
81    y = (state->mt[AV_RANDOM_N - 1] & UPPER_MASK) | (state->mt[0] & LOWER_MASK);
82    state->mt[AV_RANDOM_N - 1] = state->mt[M - 1] ^ (y >> 1) ^ ((y&1)*A);
83    state->index = 0;
84}
85
86#ifdef TEST
87#include "common.h"
88#include "log.h"
89int main(void)
90{
91    int x=0;
92    int i, j;
93    AVRandomState state;
94
95    av_random_init(&state, 0xdeadbeef);
96    for (j = 0; j < 10000; j++) {
97        START_TIMER
98        for (i = 0; i < 624; i++) {
99            x+= av_random(&state);
100        }
101        STOP_TIMER("624 calls of av_random");
102    }
103    av_log(NULL, AV_LOG_ERROR, "final value:%X\n", x);
104    return 0;
105}
106#endif
107