/* $NetBSD: random.S,v 1.6 2010/09/07 20:35:50 pooka Exp $ */ /*- * Copyright (c) 1998 The NetBSD Foundation, Inc. * All rights reserved. * * This code is derived from software contributed to The NetBSD Foundation * by Charles M. Hannum. * * Redistribution and use in source and binary forms, with or without * modification, are permitted provided that the following conditions * are met: * 1. Redistributions of source code must retain the above copyright * notice, this list of conditions and the following disclaimer. * 2. Redistributions in binary form must reproduce the above copyright * notice, this list of conditions and the following disclaimer in the * documentation and/or other materials provided with the distribution. * * THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. 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 FOUNDATION 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. */ /* * Copyright (c) 1990,1993 The Regents of the University of California. * All rights reserved. * * Redistribution and use in source and binary forms, with or without * modification, are permitted provided that: (1) source code distributions * retain the above copyright notice and this paragraph in its entirety, (2) * distributions including binary code include the above copyright notice and * this paragraph in its entirety in the documentation or other materials * provided with the distribution, and (3) all advertising materials mentioning * features or use of this software display the following acknowledgement: * ``This product includes software developed by the University of California, * Lawrence Berkeley Laboratory and its contributors.'' Neither the name of * the University nor the names of its contributors may be used to endorse * or promote products derived from this software without specific prior * written permission. * THIS SOFTWARE IS PROVIDED ``AS IS'' AND WITHOUT ANY EXPRESS OR IMPLIED * WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED WARRANTIES OF * MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE. * * Here is a very good random number generator. This implementation is * based on ``Two Fast Implementations of the "Minimal Standard" Random * Number Generator'', David G. Carta, Communications of the ACM, Jan 1990, * Vol 33 No 1. Do NOT modify this code unless you have a very thorough * understanding of the algorithm. It's trickier than you think. If * you do change it, make sure that its 10,000'th invocation returns * 1043618065. * * Here is easier-to-decipher pseudocode: * * p = (16807*seed)<30:0> # e.g., the low 31 bits of the product * q = (16807*seed)<62:31> # e.g., the high 31 bits starting at bit 32 * if (p + q < 2^31) * seed = p + q * else * seed = ((p + q) & (2^31 - 1)) + 1 * return (seed); * * The result is in (0,2^31), e.g., it's always positive. */ #include <machine/asm.h> .data randseed: .long 1 .text ENTRY(random) movl $16807,%eax PIC_PROLOGUE imull PIC_GOTOFF(randseed) PIC_EPILOGUE shld $1,%eax,%edx andl $0x7fffffff,%eax addl %edx,%eax js neg PIC_PROLOGUE movl %eax,PIC_GOTOFF(randseed) PIC_EPILOGUE ret neg: subl $0x7fffffff,%eax PIC_PROLOGUE movl %eax,PIC_GOTOFF(randseed) PIC_EPILOGUE ret |