xref: /src/lib/libc/stdlib/_rand48.c

/*	$NetBSD: _rand48.c,v 1.8 2020/02/22 11:24:47 kamil Exp $	*/

/*
 * Copyright (c) 1993 Martin Birgmeier
 * All rights reserved.
 *
 * You may redistribute unmodified or modified versions of this source
 * code provided that the above copyright notice and this and the
 * following conditions are retained.
 *
 * This software is provided ``as is'', and comes with no warranties
 * of any kind. I shall in no event be liable for anything that happens
 * to anyone/anything when using this software.
 */

#include <sys/cdefs.h>
#if defined(LIBC_SCCS) && !defined(lint)
__RCSID("$NetBSD: _rand48.c,v 1.8 2020/02/22 11:24:47 kamil Exp $");
#endif /* LIBC_SCCS and not lint */

#include <assert.h>

#include "rand48.h"

unsigned short __rand48_seed[3] = {
	RAND48_SEED_0,
	RAND48_SEED_1,
	RAND48_SEED_2
};
unsigned short __rand48_mult[3] = {
	RAND48_MULT_0,
	RAND48_MULT_1,
	RAND48_MULT_2
};
unsigned short __rand48_add = RAND48_ADD;

void
__dorand48(unsigned short xseed[3])
{
	unsigned long accu;
	unsigned short temp[2];

	_DIAGASSERT(xseed != NULL);

	accu = (unsigned long) __rand48_mult[0] * (unsigned long) xseed[0];
	accu += (unsigned long) __rand48_add;
	temp[0] = (unsigned short) accu;	/* lower 16 bits */
	accu >>= sizeof(unsigned short) * 8;
	accu += (unsigned long) __rand48_mult[0] * (unsigned long) xseed[1];
	accu += (unsigned long) __rand48_mult[1] * (unsigned long) xseed[0];
	temp[1] = (unsigned short) accu;	/* middle 16 bits */
	accu >>= sizeof(unsigned short) * 8;
	accu += __rand48_mult[0] * xseed[2] + __rand48_mult[1] * xseed[1] + __rand48_mult[2] * xseed[0];
	xseed[0] = temp[0];
	xseed[1] = temp[1];
	xseed[2] = (unsigned short) accu;
}