NetBSD/sys/lib/libkern/arch/vax/random.S

84 lines
2.7 KiB
ArmAsm

/* $NetBSD: random.S,v 1.2 2000/07/19 03:48:24 matt Exp $ */
/*
* 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.
*
* This implementation Copyright (c) 1994 Ludd, University of Lule}, Sweden
* All rights reserved.
*
* All bugs subject to removal without further notice.
*
* 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
ENTRY(random, 0)
movl $16807,r0
movl randseed,r1 # r2=16807*loword(randseed)
bicl3 $0xffff0000,r1,r2
mull2 r0,r2
ashl $-16,r1,r1 # r1=16807*hiword(randseed)
bicl2 $0xffff0000,r1
mull2 r0,r1
bicl3 $0xffff0000,r2,r0
ashl $-16,r2,r2 # r1+=(r2>>16)
bicl2 $0xffff0000,r2
addl2 r2,r1
ashl $16,r1,r2 # r0|=r1<<16
bisl2 r2,r0
ashl $-16,r1,r1 # r1=r1>>16
ashl $1,r1,r1
movl r0,r2
rotl $1,r0,r0
bicl2 $0xfffffffe,r0
bisl2 r0,r1
movl r2,r0
bicl2 $0x80000000,r0
addl2 r1,r0
bgeq L1
subl2 $0x7fffffff,r0
L1: movl r0,randseed
ret