/*
 * This rand() implementation is based on the Mersenne Twister.
 * Specifically, it's a C implementation of the pseudocode
 * implementation that can be found on the Wikipedia article for
 * the Mersenne Twister.
 *
 * Did we have to do a Mersenne Twister? No. No, we did not.
 * Did we? Fuck yes, we did.
 *
 * Love,
 *   Kat
 */

#include <stdlib.h>

static int _rand_state[624] = { 0 };
static unsigned int _rand_seed = 5489;
static int _rand_index = 625;

void _rand_init(unsigned int seed) {
  _rand_index = 624;
  _rand_state[0] = seed;
  int i = 0;
  for(i = 1; i < 624; i++) {
    _rand_state[i]  = 1812433253 ;
    _rand_state[i] *= _rand_state[i-1] ^ (_rand_state[i-1] >> 30);
    _rand_state[i] += i;
  }
}

void _rand_twist() {
  int i = 0, x, xA;
  for(i = 0; i < 624; i++) {
    x = _rand_state[i] & 0xFFFF0000 + (_rand_state[(i + 1) % 624] & 0xFFFF);
    xA = x % 2 == 0 ? x >> 1 : (x >> 1) ^ 0x9908B0DF;
    _rand_state[i] = _rand_state[(i + 397) % 624] ^ xA;
  }
  _rand_index = 0;
}

int rand(void) {
  int y;
  if(_rand_index > 624) {
    _rand_init(_rand_seed);
  }

  if(_rand_index >= 624) {
    _rand_twist();
  }

  y = _rand_state[_rand_index];
  y ^= y >> 11;
  y ^= (y << 7) & 0x9D2C5680;
  y ^= (y << 15) & 0xEFC60000;
  y ^= (y >> 18);

  _rand_index++;
  return y % RAND_MAX;
}

void srand(unsigned int seed) {
  _rand_seed = seed;
  _rand_index = 625;
}