randomkit.c

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/* Random kit 1.3 */
 
/*
 * Copyright (c) 2003-2005, Jean-Sebastien Roy (js@jeannot.org)
 *
 * The rk_random and rk_seed functions algorithms and the original design of
 * the Mersenne Twister RNG:
 *
 *   Copyright (C) 1997 - 2002, Makoto Matsumoto and Takuji Nishimura,
 *   All rights reserved.
 *
 *   Redistribution and use in source and binary forms, with or without
 *   modification, are permitted provided that the following conditions
 *   are met:
 *
 *   1. Redistributions of source code must retain the above copyright
 *   notice, this list of conditions and the following disclaimer.
 *
 *   2. Redistributions in binary form must reproduce the above copyright
 *   notice, this list of conditions and the following disclaimer in the
 *   documentation and/or other materials provided with the distribution.
 *
 *   3. The names of its contributors may not be used to endorse or promote
 *   products derived from this software without specific prior written
 *   permission.
 *
 *   THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
 *   "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
 *   LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
 *   A PARTICULAR PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE COPYRIGHT OWNER OR
 *   CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
 *   EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
 *   PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
 *   PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
 *   LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
 *   NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
 *   SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 *
 * Original algorithm for the implementation of rk_interval function from
 * Richard J. Wagner's implementation of the Mersenne Twister RNG, optimised by
 * Magnus Jonsson.
 *
 * Constants used in the rk_double implementation by Isaku Wada.
 *
 * Permission is hereby granted, free of charge, to any person obtaining a
 * copy of this software and associated documentation files (the
 * "Software"), to deal in the Software without restriction, including
 * without limitation the rights to use, copy, modify, merge, publish,
 * distribute, sublicense, and/or sell copies of the Software, and to
 * permit persons to whom the Software is furnished to do so, subject to
 * the following conditions:
 *
 * The above copyright notice and this permission notice shall be included
 * in all copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS
 * OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
 * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.
 * IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY
 * CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT,
 * TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE
 * SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
 */
 
#include "config.h"
 
#include <stddef.h>
#include <stdio.h>
#include <stdlib.h>
#include <errno.h>
#include <limits.h>
#include <math.h>
 
#include <neatogen/randomkit.h>
 
void
rk_seed(unsigned long seed, rk_state *state)
{
    int pos;
    seed &= 0xffffffffUL;
 
    /* Knuth's PRNG as used in the Mersenne Twister reference implementation */
    for (pos = 0; pos < RK_STATE_LEN; pos++) {
        state->key[pos] = seed;
        seed = (1812433253UL * (seed ^ (seed >> 30)) + pos + 1) & 0xffffffffUL;
    }
    state->pos = RK_STATE_LEN;
}
 
/* Magic Mersenne Twister constants */
#define N 624
#define M 397
#define MATRIX_A 0x9908b0dfUL
#define UPPER_MASK 0x80000000UL
#define LOWER_MASK 0x7fffffffUL
 
/* Slightly optimised reference implementation of the Mersenne Twister */
unsigned long
rk_random(rk_state *state)
{
    unsigned long y;
 
    if (state->pos == RK_STATE_LEN) {
        int i;
 
        for (i = 0; i < N - M; i++) {
            y = (state->key[i] & UPPER_MASK) | (state->key[i+1] & LOWER_MASK);
            state->key[i] = state->key[i+M] ^ (y>>1) ^ ((y & 1) * MATRIX_A);
        }
        for (; i < N - 1; i++) {
            y = (state->key[i] & UPPER_MASK) | (state->key[i+1] & LOWER_MASK);
            state->key[i] = state->key[i+(M-N)] ^ (y>>1) ^ ((y & 1) * MATRIX_A);
        }
        y = (state->key[N - 1] & UPPER_MASK) | (state->key[0] & LOWER_MASK);
        state->key[N - 1] = state->key[M - 1] ^ (y >> 1) ^ ((y & 1) * MATRIX_A);
 
        state->pos = 0;
    }
    y = state->key[state->pos++];
 
    /* Tempering */
    y ^= (y >> 11);
    y ^= (y << 7) & 0x9d2c5680UL;
    y ^= (y << 15) & 0xefc60000UL;
    y ^= (y >> 18);
 
    return y;
}
 
static unsigned long rk_ulong(rk_state *state) {
#if ULONG_MAX <= 0xffffffffUL
    return rk_random(state);
#else
    return (rk_random(state) << 32) | (rk_random(state));
#endif
}
 
unsigned long
rk_interval(unsigned long max, rk_state *state)
{
    unsigned long mask = max, value;
 
    if (max == 0) {
        return 0;
    }
    /* Smallest bit mask >= max */
    mask |= mask >> 1;
    mask |= mask >> 2;
    mask |= mask >> 4;
    mask |= mask >> 8;
    mask |= mask >> 16;
#if ULONG_MAX > 0xffffffffUL
    mask |= mask >> 32;
#endif
 
    /* Search a random value in [0..mask] <= max */
#if ULONG_MAX > 0xffffffffUL
    if (max <= 0xffffffffUL) {
        while ((value = (rk_random(state) & mask)) > max);
    }
    else {
        while ((value = (rk_ulong(state) & mask)) > max);
    }
#else
    while ((value = (rk_ulong(state) & mask)) > max);
#endif
    return value;
}