library/stdlib_rand_r.c
/*
* $Id: stdlib_rand_r.c,v 1.2 2006-01-08 12:04:26 obarthel Exp $
*
* :ts=4
*
* Portable ISO 'C' (1994) runtime library for the Amiga computer
* Copyright (c) 2002-2015 by Olaf Barthel <obarthel (at) gmx.net>
* All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
*
* - Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
*
* - Neither the name of Olaf Barthel nor the names of contributors
* may be used to endorse or promote products derived from this
* software without specific prior written permission.
*
* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
* AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
* ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
* LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
* CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
* SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
* INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
* CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
* ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
* POSSIBILITY OF SUCH DAMAGE.
*/
#ifndef _STDLIB_HEADERS_H
#include "stdlib_headers.h"
#endif /* _STDLIB_HEADERS_H */
/****************************************************************************/
/* Parameters of a pseudo-random-number generator from Knuth's
"The Art of Computer Programming, Volume 2: Seminumerical Algorithms"
(3rd edition), pp. 185-186. */
#define MM 2147483647 /* a Mersenne prime */
#define AA 48271 /* this does well in the spectral test */
#define QQ 44488 /* (long)(MM/AA) */
#define RR 3399 /* MM % AA; it is important that RR < QQ */
/****************************************************************************/
int
rand_r(unsigned int * seed)
{
int X;
X = (int)((*seed) & 0x7fffffff);
if(X == 0)
X = 1; /* NOTE: for Knuth's algorithm the seed must not be zero. */
X = AA * (X % QQ) - RR * (long)(X / QQ);
if(X < 0)
X += MM;
(*seed) = (unsigned int)X;
return(X);
}