115 lines
3.3 KiB
C
115 lines
3.3 KiB
C
// sg_random.c -- routines to handle random number generation
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//
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// Written by Curtis Olson, started July 1997.
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//
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// Copyright (C) 1997 Curtis L. Olson - http://www.flightgear.org/~curt
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//
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// This library is free software; you can redistribute it and/or
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// modify it under the terms of the GNU Library General Public
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// License as published by the Free Software Foundation; either
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// version 2 of the License, or (at your option) any later version.
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//
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// This library is distributed in the hope that it will be useful,
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// but WITHOUT ANY WARRANTY; without even the implied warranty of
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// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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// Library General Public License for more details.
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//
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// You should have received a copy of the GNU General Public License
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// along with this program; if not, write to the Free Software
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// Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
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//
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// $Id$
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/*
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* "Cleaned up" and simplified Mersenne Twister implementation.
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* Vastly smaller and more easily understood and embedded. Stores the
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* state in a user-maintained structure instead of static memory, so
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* you can have more than one, or save snapshots of the RNG state.
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* Lacks the "init_by_array()" feature of the original code in favor
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* of the simpler 32 bit seed initialization. Lacks the floating
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* point generator, which is an orthogonal problem not related to
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* random number generation. Verified to be identical to the original
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* MT199367ar code through the first 10M generated numbers.
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*/
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#ifdef HAVE_CONFIG_H
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# include <simgear_config.h>
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#endif
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#include <stdio.h>
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#include <stdlib.h> // for random(), srandom()
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#include <time.h> // for time() to seed srandom()
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#include "sg_random.h"
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// Structure for the random number functions.
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mt random_seed;
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#define MT(i) mt->array[i]
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void mt_init(mt *mt, unsigned int seed)
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{
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int i;
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MT(0)= seed;
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for(i=1; i<MT_N; i++)
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MT(i) = (1812433253 * (MT(i-1) ^ (MT(i-1) >> 30)) + i);
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mt->index = MT_N+1;
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}
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void mt_init_time_10(mt *mt)
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{
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mt_init(mt, (unsigned int) time(NULL) / 600);
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}
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unsigned int mt_rand32(mt *mt)
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{
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unsigned int i, y;
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if(mt->index >= MT_N) {
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for(i=0; i<MT_N; i++) {
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y = (MT(i) & 0x80000000) | (MT((i+1)%MT_N) & 0x7fffffff);
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MT(i) = MT((i+MT_M)%MT_N) ^ (y>>1) ^ (y&1 ? 0x9908b0df : 0);
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}
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mt->index = 0;
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}
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y = MT(mt->index++);
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y ^= (y >> 11);
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y ^= (y << 7) & 0x9d2c5680;
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y ^= (y << 15) & 0xefc60000;
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y ^= (y >> 18);
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return y;
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}
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double mt_rand(mt *mt)
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{
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/* divided by 2^32-1 */
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return (double)mt_rand32(mt) * (1.0/4294967295.0);
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}
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// Seed the random number generater with time() so we don't see the
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// same sequence every time
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void sg_srandom_time() {
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mt_init(&random_seed, (unsigned int) time(NULL));
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}
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// Seed the random number generater with time() in 10 minute intervals
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// so we get the same sequence within 10 minutes interval.
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// This is useful for synchronizing two display systems.
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void sg_srandom_time_10() {
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mt_init(&random_seed, (unsigned int) time(NULL) / 600);
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}
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// Seed the random number generater with your own seed so can set up
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// repeatable randomization.
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void sg_srandom( unsigned int seed ) {
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mt_init(&random_seed, seed);
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}
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// return a random number between [0.0, 1.0)
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double sg_random() {
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return mt_rand(&random_seed);
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}
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