164 lines
5.3 KiB
C
164 lines
5.3 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 Library General Public
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// License along with this library; if not, write to the
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// Free Software Foundation, Inc., 59 Temple Place - Suite 330,
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// Boston, MA 02111-1307, USA.
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//
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// $Id$
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/*
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A C-program for MT19937, with initialization improved 2002/2/10.
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Coded by Takuji Nishimura and Makoto Matsumoto.
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This is a faster version by taking Shawn Cokus's optimization,
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Matthe Bellew's simplification, Isaku Wada's real version.
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Before using, initialize the state by using init_genrand(seed)
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or init_by_array(init_key, key_length).
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Copyright (C) 1997 - 2002, Makoto Matsumoto and Takuji Nishimura,
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All rights reserved.
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Redistribution and use in source and binary forms, with or without
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modification, are permitted provided that the following conditions
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are met:
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1. Redistributions of source code must retain the above copyright
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notice, this list of conditions and the following disclaimer.
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2. Redistributions in binary form must reproduce the above copyright
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notice, this list of conditions and the following disclaimer in the
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documentation and/or other materials provided with the distribution.
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3. The names of its contributors may not be used to endorse or promote
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products derived from this software without specific prior written
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permission.
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THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
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"AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
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LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
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A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR
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CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
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EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
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PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
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PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
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LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
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NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
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SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
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Any feedback is very welcome.
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http://www.math.keio.ac.jp/matumoto/emt.html
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email: matumoto@math.keio.ac.jp
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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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/* Period parameters */
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#define N 624
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#define M 397
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#define MATRIX_A 0x9908b0dfUL /* constant vector a */
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#define UMASK 0x80000000UL /* most significant w-r bits */
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#define LMASK 0x7fffffffUL /* least significant r bits */
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#define MIXBITS(u,v) ( ((u) & UMASK) | ((v) & LMASK) )
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#define TWIST(u,v) ((MIXBITS(u,v) >> 1) ^ ((v)&1UL ? MATRIX_A : 0UL))
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static unsigned long state[N]; /* the array for the state vector */
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static int left = 1;
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static int initf = 0;
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static unsigned long *next;
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/* initializes state[N] with a seed */
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void init_genrand(unsigned long s)
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{
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int j;
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state[0]= s & 0xffffffffUL;
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for (j=1; j<N; j++) {
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state[j] = (1812433253UL * (state[j-1] ^ (state[j-1] >> 30)) + j);
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/* See Knuth TAOCP Vol2. 3rd Ed. P.106 for multiplier. */
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/* In the previous versions, MSBs of the seed affect */
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/* only MSBs of the array state[]. */
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/* 2002/01/09 modified by Makoto Matsumoto */
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state[j] &= 0xffffffffUL; /* for >32 bit machines */
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}
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left = 1; initf = 1;
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}
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static void next_state(void)
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{
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unsigned long *p=state;
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int j;
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/* if init_genrand() has not been called, */
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/* a default initial seed is used */
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if (initf==0) init_genrand(5489UL);
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left = N;
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next = state;
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for (j=N-M+1; --j; p++)
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*p = p[M] ^ TWIST(p[0], p[1]);
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for (j=M; --j; p++)
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*p = p[M-N] ^ TWIST(p[0], p[1]);
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*p = p[M-N] ^ TWIST(p[0], state[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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init_genrand(time(NULL));
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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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init_genrand( 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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unsigned long y;
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if (--left == 0)
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next_state();
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y = *next++;
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/* Tempering */
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y ^= (y >> 11);
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y ^= (y << 7) & 0x9d2c5680UL;
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y ^= (y << 15) & 0xefc60000UL;
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y ^= (y >> 18);
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return (double)y * (1.0/4294967295.0);
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/* divided by 2^32-1 */
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}
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