_rand48.c

来自「基于组件方式开发操作系统的OSKIT源代码」· C语言 代码 · 共 47 行

/*
 * 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 "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];

	accu = (unsigned long) _rand48_mult[0] * (unsigned long) xseed[0] +
	 (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] +
	 (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;
}