1/* $NetBSD: random.S,v 1.4 2007/01/14 13:26:18 ragge Exp $ */ 2 3/* 4 * Copyright (c) 1994 Ludd, University of Lule}, Sweden. All rights reserved. 5 * 6 * Redistribution and use in source and binary forms, with or without 7 * modification, are permitted provided that the following conditions 8 * are met: 9 * 1. Redistributions of source code must retain the above copyright 10 * notice, this list of conditions and the following disclaimer. 11 * 2. Redistributions in binary form must reproduce the above copyright 12 * notice, this list of conditions and the following disclaimer in the 13 * documentation and/or other materials provided with the distribution. 14 * 3. The name of the author may not be used to endorse or promote products 15 * derived from this software without specific prior written permission 16 * 17 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR 18 * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES 19 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. 20 * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT, 21 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT 22 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, 23 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY 24 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT 25 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF 26 * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. 27 */ 28 29/* 30 * Copyright (c) 1990,1993 The Regents of the University of California. 31 * All rights reserved. 32 * 33 * Redistribution and use in source and binary forms, with or without 34 * modification, are permitted provided that: (1) source code distributions 35 * retain the above copyright notice and this paragraph in its entirety, (2) 36 * distributions including binary code include the above copyright notice and 37 * this paragraph in its entirety in the documentation or other materials 38 * provided with the distribution, and (3) all advertising materials mentioning 39 * features or use of this software display the following acknowledgement: 40 * ``This product includes software developed by the University of California, 41 * Lawrence Berkeley Laboratory and its contributors.'' Neither the name of 42 * the University nor the names of its contributors may be used to endorse 43 * or promote products derived from this software without specific prior 44 * written permission. 45 * THIS SOFTWARE IS PROVIDED ``AS IS'' AND WITHOUT ANY EXPRESS OR IMPLIED 46 * WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED WARRANTIES OF 47 * MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE. 48 * 49 * Here is a very good random number generator. This implementation is 50 * based on ``Two Fast Implementations of the "Minimal Standard" Random 51 * Number Generator'', David G. Carta, Communications of the ACM, Jan 1990, 52 * Vol 33 No 1. Do NOT modify this code unless you have a very thorough 53 * understanding of the algorithm. It's trickier than you think. If 54 * you do change it, make sure that its 10,000'th invocation returns 55 * 1043618065. 56 * 57 * Here is easier-to-decipher pseudocode: 58 * 59 * p = (16807*seed)<30:0> # e.g., the low 31 bits of the product 60 * q = (16807*seed)<62:31> # e.g., the high 31 bits starting at bit 32 61 * if (p + q < 2^31) 62 * seed = p + q 63 * else 64 * seed = ((p + q) & (2^31 - 1)) + 1 65 * return (seed); 66 * 67 * The result is in (0,2^31), e.g., it's always positive. 68 */ 69 70#include <machine/asm.h> 71 72 .data 73randseed: 74 .long 1 75 76ENTRY(random, 0) 77 movl $16807,%r0 78 79 movl randseed,%r1 # %r2=16807*loword(randseed) 80 bicl3 $0xffff0000,%r1,%r2 81 mull2 %r0,%r2 82 ashl $-16,%r1,%r1 # %r1=16807*hiword(randseed) 83 bicl2 $0xffff0000,%r1 84 mull2 %r0,%r1 85 bicl3 $0xffff0000,%r2,%r0 86 ashl $-16,%r2,%r2 # %r1+=(%r2>>16) 87 bicl2 $0xffff0000,%r2 88 addl2 %r2,%r1 89 ashl $16,%r1,%r2 # %r0|=%r1<<16 90 bisl2 %r2,%r0 91 ashl $-16,%r1,%r1 # %r1=%r1>>16 92 93 ashl $1,%r1,%r1 94 movl %r0,%r2 95 rotl $1,%r0,%r0 96 bicl2 $0xfffffffe,%r0 97 bisl2 %r0,%r1 98 movl %r2,%r0 99 bicl2 $0x80000000,%r0 100 addl2 %r1,%r0 101 bgeq L1 102 subl2 $0x7fffffff,%r0 103L1: movl %r0,randseed 104 ret 105