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/* $OpenBSD: random.S,v 1.2 2001/08/20 20:15:29 jason Exp $ */
/* $NetBSD: random.S,v 1.1.1.1 1998/06/20 05:18:14 eeh 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.
*
* 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
.text
ENTRY(random)
sethi %hi(16807), %o1
wr %o1, %lo(16807), %y
sethi %hi(randseed), %g1
ld [%g1 + %lo(randseed)], %o0
andcc %g0, 0, %o2
mulscc %o2, %o0, %o2
mulscc %o2, %o0, %o2
mulscc %o2, %o0, %o2
mulscc %o2, %o0, %o2
mulscc %o2, %o0, %o2
mulscc %o2, %o0, %o2
mulscc %o2, %o0, %o2
mulscc %o2, %o0, %o2
mulscc %o2, %o0, %o2
mulscc %o2, %o0, %o2
mulscc %o2, %o0, %o2
mulscc %o2, %o0, %o2
mulscc %o2, %o0, %o2
mulscc %o2, %o0, %o2
mulscc %o2, %o0, %o2
mulscc %o2, %g0, %o2
rd %y, %o3
srl %o2, 16, %o1
set 0xffff, %o4
and %o4, %o2, %o0
sll %o0, 15, %o0
srl %o3, 17, %o3
or %o3, %o0, %o0
addcc %o0, %o1, %o0
bneg 1f
sethi %hi(0x7fffffff), %o1
retl
st %o0, [%g1 + %lo(randseed)]
1:
or %o1, %lo(0x7fffffff), %o1
add %o0, 1, %o0
and %o1, %o0, %o0
retl
st %o0, [%g1 + %lo(randseed)]
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