/**
 * @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
 */

/* Note: this is a stripped-down version of TinyMT that only includes the
   32-bit integer generator. For the full version, please see
     <https://github.com/MersenneTwister-Lab/TinyMT>. */

#include "tinymt32.h"

#define TINYMT32_SH0 1
#define TINYMT32_SH1 10
#define TINYMT32_SH8 8
#define TINYMT32_MASK 0x7fffffff

/**
 * This function changes internal state of tinymt32.
 * Users should not call this function directly.
 * @param random tinymt internal status
 */
static void tinymt32_next_state(tinymt32_t * random) {
    uint32_t x;
    uint32_t y;

    y = random->status[3];
    x = (random->status[0] & TINYMT32_MASK)
        ^ random->status[1]
        ^ random->status[2];
    x ^= (x << TINYMT32_SH0);
    y ^= (y >> TINYMT32_SH0) ^ x;
    random->status[0] = random->status[1];
    random->status[1] = random->status[2];
    random->status[2] = x ^ (y << TINYMT32_SH1);
    random->status[3] = y;
    random->status[1] ^= -((int32_t)(y & 1)) & random->mat1;
    random->status[2] ^= -((int32_t)(y & 1)) & random->mat2;
}

/**
 * This function outputs 32-bit unsigned integer from internal state.
 * Users should not call this function directly.
 * @param random tinymt internal status
 * @return 32-bit unsigned pseudorandom number
 */
static uint32_t tinymt32_temper(tinymt32_t * random) {
    uint32_t t0, t1;
    t0 = random->status[3];
#if defined(LINEARITY_CHECK)
    t1 = random->status[0]
        ^ (random->status[2] >> TINYMT32_SH8);
#else
    t1 = random->status[0]
        + (random->status[2] >> TINYMT32_SH8);
#endif
    t0 ^= t1;
    t0 ^= -((int32_t)(t1 & 1)) & random->tmat;
    return t0;
}

/**
 * This function outputs 32-bit unsigned integer from internal state.
 * @param random tinymt internal status
 * @return 32-bit unsigned integer r (0 <= r < 2^32)
 */
uint32_t tinymt32_generate_uint32(tinymt32_t * random) {
    tinymt32_next_state(random);
    return tinymt32_temper(random);
}

#define MIN_LOOP 8
#define PRE_LOOP 8

/**
 * 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 (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 (int i = 0; i < PRE_LOOP; i++) {
    tinymt32_next_state(random);
    }
}