1/* $NetBSD: random.S,v 1.2 2008/04/28 20:24:06 martin Exp $ */ 2 3/*- 4 * Copyright (c) 1998 The NetBSD Foundation, Inc. 5 * All rights reserved. 6 * 7 * This code is derived from software contributed to The NetBSD Foundation 8 * by Charles M. Hannum. 9 * 10 * Redistribution and use in source and binary forms, with or without 11 * modification, are permitted provided that the following conditions 12 * are met: 13 * 1. Redistributions of source code must retain the above copyright 14 * notice, this list of conditions and the following disclaimer. 15 * 2. Redistributions in binary form must reproduce the above copyright 16 * notice, this list of conditions and the following disclaimer in the 17 * documentation and/or other materials provided with the distribution. 18 * 19 * THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS 20 * ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED 21 * TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR 22 * PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS 23 * BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR 24 * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF 25 * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS 26 * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN 27 * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) 28 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE 29 * POSSIBILITY OF SUCH DAMAGE. 30 */ 31 32/* 33 * Copyright (c) 1990,1993 The Regents of the University of California. 34 * All rights reserved. 35 * 36 * Redistribution and use in source and binary forms, with or without 37 * modification, are permitted provided that: (1) source code distributions 38 * retain the above copyright notice and this paragraph in its entirety, (2) 39 * distributions including binary code include the above copyright notice and 40 * this paragraph in its entirety in the documentation or other materials 41 * provided with the distribution, and (3) all advertising materials mentioning 42 * features or use of this software display the following acknowledgement: 43 * ``This product includes software developed by the University of California, 44 * Lawrence Berkeley Laboratory and its contributors.'' Neither the name of 45 * the University nor the names of its contributors may be used to endorse 46 * or promote products derived from this software without specific prior 47 * written permission. 48 * THIS SOFTWARE IS PROVIDED ``AS IS'' AND WITHOUT ANY EXPRESS OR IMPLIED 49 * WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED WARRANTIES OF 50 * MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE. 51 * 52 * Here is a very good random number generator. This implementation is 53 * based on ``Two Fast Implementations of the "Minimal Standard" Random 54 * Number Generator'', David G. Carta, Communications of the ACM, Jan 1990, 55 * Vol 33 No 1. Do NOT modify this code unless you have a very thorough 56 * understanding of the algorithm. It's trickier than you think. If 57 * you do change it, make sure that its 10,000'th invocation returns 58 * 1043618065. 59 * 60 * Here is easier-to-decipher pseudocode: 61 * 62 * p = (16807*seed)<30:0> # e.g., the low 31 bits of the product 63 * q = (16807*seed)<62:31> # e.g., the high 31 bits starting at bit 32 64 * if (p + q < 2^31) 65 * seed = p + q 66 * else 67 * seed = ((p + q) & (2^31 - 1)) + 1 68 * return (seed); 69 * 70 * The result is in (0,2^31), e.g., it's always positive. 71 */ 72#include <machine/asm.h> 73 74 .data 75randseed: 76 .long 1 77 .text 78ENTRY(random) 79 movl $16807,%eax 80 imull randseed(%rip) 81 shld $1,%eax,%edx 82 andl $0x7fffffff,%eax 83 addl %edx,%eax 84 js 1f 85 movl %eax,randseed(%rip) 86 ret 871: 88 subl $0x7fffffff,%eax 89 movl %eax,randseed(%rip) 90 ret 91