1/* $NetBSD: random.S,v 1.3 2002/02/24 00:08:23 matt Exp $ */ 2 3/* 4 * Copyright (c) 1990,1993 The Regents of the University of California. 5 * All rights reserved. 6 * 7 * Redistribution and use in source and binary forms, with or without 8 * modification, are permitted provided that: (1) source code distributions 9 * retain the above copyright notice and this paragraph in its entirety, (2) 10 * distributions including binary code include the above copyright notice and 11 * this paragraph in its entirety in the documentation or other materials 12 * provided with the distribution, and (3) all advertising materials mentioning 13 * features or use of this software display the following acknowledgement: 14 * ``This product includes software developed by the University of California, 15 * Lawrence Berkeley Laboratory and its contributors.'' Neither the name of 16 * the University nor the names of its contributors may be used to endorse 17 * or promote products derived from this software without specific prior 18 * written permission. 19 * THIS SOFTWARE IS PROVIDED ``AS IS'' AND WITHOUT ANY EXPRESS OR IMPLIED 20 * WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED WARRANTIES OF 21 * MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE. 22 * 23 * Here is a very good random number generator. This implementation is 24 * based on ``Two Fast Implementations of the "Minimal Standard" Random 25 * Number Generator'', David G. Carta, Communications of the ACM, Jan 1990, 26 * Vol 33 No 1. Do NOT modify this code unless you have a very thorough 27 * understanding of the algorithm. It's trickier than you think. If 28 * you do change it, make sure that its 10,000'th invocation returns 29 * 1043618065. 30 * 31 * This implementation Copyright (c) 1994 Ludd, University of Lule}, Sweden 32 * All rights reserved. 33 * 34 * All bugs subject to removal without further notice. 35 * 36 * Here is easier-to-decipher pseudocode: 37 * 38 * p = (16807*seed)<30:0> # e.g., the low 31 bits of the product 39 * q = (16807*seed)<62:31> # e.g., the high 31 bits starting at bit 32 40 * if (p + q < 2^31) 41 * seed = p + q 42 * else 43 * seed = ((p + q) & (2^31 - 1)) + 1 44 * return (seed); 45 * 46 * The result is in (0,2^31), e.g., it's always positive. 47 */ 48 49#include <machine/asm.h> 50 51 .data 52randseed: 53 .long 1 54 55ENTRY(random, 0) 56 movl $16807,%r0 57 58 movl randseed,%r1 # %r2=16807*loword(randseed) 59 bicl3 $0xffff0000,%r1,%r2 60 mull2 %r0,%r2 61 ashl $-16,%r1,%r1 # %r1=16807*hiword(randseed) 62 bicl2 $0xffff0000,%r1 63 mull2 %r0,%r1 64 bicl3 $0xffff0000,%r2,%r0 65 ashl $-16,%r2,%r2 # %r1+=(%r2>>16) 66 bicl2 $0xffff0000,%r2 67 addl2 %r2,%r1 68 ashl $16,%r1,%r2 # %r0|=%r1<<16 69 bisl2 %r2,%r0 70 ashl $-16,%r1,%r1 # %r1=%r1>>16 71 72 ashl $1,%r1,%r1 73 movl %r0,%r2 74 rotl $1,%r0,%r0 75 bicl2 $0xfffffffe,%r0 76 bisl2 %r0,%r1 77 movl %r2,%r0 78 bicl2 $0x80000000,%r0 79 addl2 %r1,%r0 80 bgeq L1 81 subl2 $0x7fffffff,%r0 82L1: movl %r0,randseed 83 ret 84