tinymt32.c

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/**
 * @file tinymt32.c
 *
 * @brief Tiny Mersenne Twister only 127 bit internal state
 *
 * @author Mutsuo Saito (Hiroshima University)
 * @author Makoto Matsumoto (The University of Tokyo)
 *
 * Copyright (C) 2011 Mutsuo Saito, Makoto Matsumoto,
 * Hiroshima University and The University of Tokyo.
 * All rights reserved.
 *
 * The 3-clause BSD License is applied to this software, see
 * LICENSE.txt
 */
#include "tinymt32.h"
#define MIN_LOOP 8
#define PRE_LOOP 8
 
/**
 * This function represents a function used in the initialization
 * by init_by_array
 * @param x 32-bit integer
 * @return 32-bit integer
 */
static uint32_t ini_func1(uint32_t x) {
    return (x ^ (x >> 27)) * UINT32_C(1664525);
}
 
/**
 * This function represents a function used in the initialization
 * by init_by_array
 * @param x 32-bit integer
 * @return 32-bit integer
 */
static uint32_t ini_func2(uint32_t x) {
    return (x ^ (x >> 27)) * UINT32_C(1566083941);
}
 
/**
 * This function certificate the period of 2^127-1.
 * @param random tinymt state vector.
 */
static void period_certification(tinymt32_t * random) {
    if ((random->status[0] & TINYMT32_MASK) == 0 &&
        random->status[1] == 0 &&
        random->status[2] == 0 &&
        random->status[3] == 0) {
        random->status[0] = 'T';
        random->status[1] = 'I';
        random->status[2] = 'N';
        random->status[3] = 'Y';
    }
}
 
/**
 * This function initializes the internal state array with a 32-bit
 * unsigned integer seed.
 * @param random tinymt state vector.
 * @param seed a 32-bit unsigned integer used as a seed.
 */
void tinymt32_init(tinymt32_t * random, uint32_t seed) {
    random->status[0] = seed;
    random->status[1] = random->mat1;
    random->status[2] = random->mat2;
    random->status[3] = random->tmat;
    for (unsigned int i = 1; i < MIN_LOOP; i++) {
        random->status[i & 3] ^= i + UINT32_C(1812433253)
            * (random->status[(i - 1) & 3]
               ^ (random->status[(i - 1) & 3] >> 30));
    }
    period_certification(random);
    for (unsigned int i = 0; i < PRE_LOOP; i++) {
        tinymt32_next_state(random);
    }
}
 
/**
 * This function initializes the internal state array,
 * with an array of 32-bit unsigned integers used as seeds
 * @param random tinymt state vector.
 * @param init_key the array of 32-bit integers, used as a seed.
 * @param key_length the length of init_key.
 */
void tinymt32_init_by_array(tinymt32_t * random, uint32_t init_key[],
                            int key_length) {
    const unsigned int lag = 1;
    const unsigned int mid = 1;
    const unsigned int size = 4;
    unsigned int i, j;
    unsigned int count;
    uint32_t r;
    uint32_t * st = &random->status[0];
 
    st[0] = 0;
    st[1] = random->mat1;
    st[2] = random->mat2;
    st[3] = random->tmat;
    if (key_length + 1 > MIN_LOOP) {
        count = (unsigned int)key_length + 1;
    } else {
        count = MIN_LOOP;
    }
    r = ini_func1(st[0] ^ st[mid % size]
                  ^ st[(size - 1) % size]);
    st[mid % size] += r;
    r += (unsigned int)key_length;
    st[(mid + lag) % size] += r;
    st[0] = r;
    count--;
    for (i = 1, j = 0; (j < count) && (j < (unsigned int)key_length); j++) {
        r = ini_func1(st[i % size]
                      ^ st[(i + mid) % size]
                      ^ st[(i + size - 1) % size]);
        st[(i + mid) % size] += r;
        r += init_key[j] + i;
        st[(i + mid + lag) % size] += r;
        st[i % size] = r;
        i = (i + 1) % size;
    }
    for (; j < count; j++) {
        r = ini_func1(st[i % size]
                      ^ st[(i + mid) % size]
                      ^ st[(i + size - 1) % size]);
        st[(i + mid) % size] += r;
        r += i;
        st[(i + mid + lag) % size] += r;
        st[i % size] = r;
        i = (i + 1) % size;
    }
    for (j = 0; j < size; j++) {
        r = ini_func2(st[i % size]
                      + st[(i + mid) % size]
                      + st[(i + size - 1) % size]);
        st[(i + mid) % size] ^= r;
        r -= i;
        st[(i + mid + lag) % size] ^= r;
        st[i % size] = r;
        i = (i + 1) % size;
    }
    period_certification(random);
    for (i = 0; i < PRE_LOOP; i++) {
        tinymt32_next_state(random);
    }
}