/*
 * A simple Mersenne Twister implementation in C
 * Author: Nicholas Kamper (kampernj@rose-hulman.edu)
 * 
 * Based on http://en.wikipedia.org/wiki/Mersenne_twister#Pseudocode
 */
#include <stdlib.h>
#include <stdio.h>
#include <stdint.h>
#include <time.h>

#include "mt.h"

int mt_currentIndex = 0;
uint32_t mt_state[MT_SIZE];

void mt_seed(uint32_t seed) {
	if (seed == 0) {
		seed = time(NULL);
	}
	
	mt_state[0] = seed;
	
	int index;
	for (index = 1; index < MT_SIZE; index++) {
		mt_state[index] = (MT_INIT_COEF * (mt_state[index - 1] ^ (mt_state[index - 1] >> 30)) + index) & MT_32B_MASK;
	}
	mt_currentIndex = 0;
}

void mt_generateNumbers() {
	int index;
	for (index = 0; index < MT_SIZE; index++) {
		uint32_t y = (mt_state[index] & 0x80000000)|(mt_state[(index + 1) % 624] & 0x7FFFFFFF);
		mt_state[index]  = mt_state[(index + 397) % 624] ^ (y >> 1);
		if ((y % 2) != 0) {
			mt_state[index] = mt_state[index] ^ 0x9908B0DF;
		}
	}
}

uint32_t mt_rand(uint32_t max) {
	if (mt_state[0] == 0) { 
		mt_seed(0);
	}

	if (mt_currentIndex == 0) {
		mt_generateNumbers();
	}

	uint32_t y = mt_state[mt_currentIndex];
	y = y ^ (y >> 11);
	y = y ^ ((y << 7) & MT_SB_COEF);
	y = y ^ ((y << 15) & MT_TC_COEF);
	y = y ^ (y >> 18);
	
	mt_currentIndex = (mt_currentIndex + 1) % 624;

	return y % max;
}