tibia-rme/source/mt_rand.cpp

//////////////////////////////////////////////////////////////////////
// This file is part of Remere's Map Editor
//////////////////////////////////////////////////////////////////////
// Remere's Map Editor is free software: you can redistribute it and/or modify
// it under the terms of the GNU General Public License as published by
// the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.
//
// Remere's Map Editor is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
// GNU General Public License for more details.
//
// You should have received a copy of the GNU General Public License
// along with this program. If not, see <http://www.gnu.org/licenses/>.
//////////////////////////////////////////////////////////////////////

#include "main.h"

static inline unsigned long int mt_get(void* vstate);
static double mt_get_double(void* vstate);
static void mt_set(void* state, unsigned long int s);

#define N 624 /* Period parameters */
#define M 397

/* most significant w-r bits */
static const unsigned long UPPER_MASK = 0x80000000UL;

/* least significant r bits */
static const unsigned long LOWER_MASK = 0x7fffffffUL;

typedef struct
{
	unsigned long mt[N];
	int mti;
} mt_state_t;

static inline unsigned long
mt_get(void* vstate) {
	mt_state_t* state = (mt_state_t*)vstate;

	unsigned long k;
	unsigned long int* const mt = state->mt;

#define MAGIC(y) (((y)&0x1) ? 0x9908b0dfUL : 0)

	if (state->mti >= N) { /* generate N words at one time */
		int kk;

		for (kk = 0; kk < N - M; kk++) {
			unsigned long y = (mt[kk] & UPPER_MASK) | (mt[kk + 1] & LOWER_MASK);
			mt[kk] = mt[kk + M] ^ (y >> 1) ^ MAGIC(y);
		}
		for (; kk < N - 1; kk++) {
			unsigned long y = (mt[kk] & UPPER_MASK) | (mt[kk + 1] & LOWER_MASK);
			mt[kk] = mt[kk + (M - N)] ^ (y >> 1) ^ MAGIC(y);
		}

		{
			unsigned long y = (mt[N - 1] & UPPER_MASK) | (mt[0] & LOWER_MASK);
			mt[N - 1] = mt[M - 1] ^ (y >> 1) ^ MAGIC(y);
		}

		state->mti = 0;
	}

	/* Tempering */

	k = mt[state->mti];
	k ^= (k >> 11);
	k ^= (k << 7) & 0x9d2c5680UL;
	k ^= (k << 15) & 0xefc60000UL;
	k ^= (k >> 18);

	state->mti++;

	return k;
}

static double
mt_get_double(void* vstate) {
	return mt_get(vstate) / 4294967296.0;
}

static void
mt_set(void* vstate, unsigned long int s) {
	mt_state_t* state = (mt_state_t*)vstate;
	int i;

	if (s == 0) {
		s = 4357; /* the default seed is 4357 */
	}

	state->mt[0] = s & 0xffffffffUL;

	for (i = 1; i < N; i++) {
		/* See Knuth's "Art of Computer Programming" Vol. 2, 3rd
		   Ed. p.106 for multiplier. */

		state->mt[i] = (1812433253UL * (state->mt[i - 1] ^ (state->mt[i - 1] >> 30)) + i);

		state->mt[i] &= 0xffffffffUL;
	}

	state->mti = i;
}

static mt_state_t mt_state;

void mt_seed(unsigned long s) {
	mt_set(&mt_state, s);
}

unsigned long mt_randi() {
	return mt_get(&mt_state);
}

double mt_randd() {
	return mt_get_double(&mt_state);
}