1/* $NetBSD: random.S,v 1.3 2009/01/05 01:16:09 pooka 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 * Here is easier-to-decipher pseudocode: 32 * 33 * p = (16807*seed)<30:0> # e.g., the low 31 bits of the product 34 * q = (16807*seed)<62:31> # e.g., the high 31 bits starting at bit 32 35 * if (p + q < 2^31) 36 * seed = p + q 37 * else 38 * seed = ((p + q) & (2^31 - 1)) + 1 39 * return (seed); 40 * 41 * The result is in (0,2^31), e.g., it's always positive. 42 */ 43#include <machine/asm.h> 44 45 .data 46randseed: 47 .long 1 48 49 .text 50ENTRY(random) 51 sethi %hi(16807), %o1 52 wr %o1, %lo(16807), %y 53#ifdef PIC 54 PIC_PROLOGUE(%o5, %o2) 55 set randseed, %g1 56 ld [%o5 + %g1], %g1 57 ld [%g1], %o0 58#else 59 sethi %hi(randseed), %g1 60 ld [%g1 + %lo(randseed)], %o0 61#endif 62 andcc %g0, 0, %o2 63 mulscc %o2, %o0, %o2 64 mulscc %o2, %o0, %o2 65 mulscc %o2, %o0, %o2 66 mulscc %o2, %o0, %o2 67 mulscc %o2, %o0, %o2 68 mulscc %o2, %o0, %o2 69 mulscc %o2, %o0, %o2 70 mulscc %o2, %o0, %o2 71 mulscc %o2, %o0, %o2 72 mulscc %o2, %o0, %o2 73 mulscc %o2, %o0, %o2 74 mulscc %o2, %o0, %o2 75 mulscc %o2, %o0, %o2 76 mulscc %o2, %o0, %o2 77 mulscc %o2, %o0, %o2 78 mulscc %o2, %g0, %o2 79 rd %y, %o3 80 srl %o2, 16, %o1 81 set 0xffff, %o4 82 and %o4, %o2, %o0 83 sll %o0, 15, %o0 84 srl %o3, 17, %o3 85 or %o3, %o0, %o0 86 addcc %o0, %o1, %o0 87 bneg 1f 88 sethi %hi(0x7fffffff), %o1 89 retl 90#ifdef PIC 91 st %o0, [%g1] 92#else 93 st %o0, [%g1 + %lo(randseed)] 94#endif 951: 96 or %o1, %lo(0x7fffffff), %o1 97 add %o0, 1, %o0 98 and %o1, %o0, %o0 99 retl 100#ifdef PIC 101 st %o0, [%g1] 102#else 103 st %o0, [%g1 + %lo(randseed)] 104#endif 105