#include "mtwister.h"

// The upper 32 bits mask
#define UPPER_MASK 0x80000000
// THe lower 32-bits mask (equivalent to the NOT of UPPER_MASK)
#define LOWER_MASK 0x7fffffff
#define TEMPERING_MASK_B 0x9d2c5680
#define TEMPERING_MASK_C 0xefc60000

static void mtrand_seed (u64 seed, struct mtrand_state *out_generator) {
	/* set initial seeds to mt[STATE_VECTOR_LENGTH] using the generator
	 * from Line 25 of Table 1 in: Donald Knuth, "The Art of Computer
	 * Programming," Vol. 2 (2nd Ed.) pp.102.
	 */
	out_generator->mt[0] = seed & 0xffffffff;
	for (out_generator->index = 1; out_generator->index < STATE_VECTOR_LENGTH; out_generator->index++) {
		out_generator->mt[out_generator->index] = (6069 * out_generator->mt[out_generator->index - 1]) & 0xffffffff;
	}
}

mtrand_state mtrand_create (u64 seed) {
	mtrand_state generator;
	mtrand_seed(seed, &generator);
	return generator;
}

u64 mtrand_generate (mtrand_state *generator) {
	u64 result;
	static u64 mag[2] = {0x0, 0x9908b0df}; /* mag[x] = x * 0x9908b0df for x = 0,1 */
	if (generator->index >= STATE_VECTOR_LENGTH || generator->index < 0) {
		/* generate STATE_VECTOR_LENGTH words at a time */
		if (generator->index >= STATE_VECTOR_LENGTH + 1 || generator->index < 0) {
			mtrand_seed(4357, generator);
		}

		i32 key;
		for (key = 0; key < STATE_VECTOR_LENGTH - STATE_VECTOR_M; key++) {
			result = (generator->mt[key] & UPPER_MASK) | (generator->mt[key + 1] & LOWER_MASK);
			generator->mt[key] = generator->mt[key + STATE_VECTOR_M] ^ (result >> 1) ^ mag[result & 0x1];
		}
		for (; key < STATE_VECTOR_LENGTH - 1; key++) {
			result = (generator->mt[key] & UPPER_MASK) | (generator->mt[key + 1] & LOWER_MASK);
			generator->mt[key] = generator->mt[key + (STATE_VECTOR_M - STATE_VECTOR_LENGTH)] ^ (result >> 1) ^ mag[result & 0x1];
		}
		result = (generator->mt[STATE_VECTOR_LENGTH - 1] & UPPER_MASK) | (generator->mt[0] & LOWER_MASK);
		generator->mt[STATE_VECTOR_LENGTH - 1] = generator->mt[STATE_VECTOR_M - 1] ^ (result >> 1) ^ mag[result & 0x1];
		generator->index = 0;
	}
	result = generator->mt[generator->index++];
	result ^= (result >> 11);
	result ^= (result << 7) & TEMPERING_MASK_B;
	result ^= (result << 15) & TEMPERING_MASK_C;
	result ^= (result >> 18);
	return result;
}

f64 mtrand_generate_d (mtrand_state *generator) {
	return ((f64)mtrand_generate(generator) / (u64)0xffffffff);
}