/* $NetBSD: random.S,v 1.4 2007/01/14 13:26:18 ragge Exp $ */
/*
* Copyright (c) 1994 Ludd, University of Lule}, Sweden. All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
* 1. Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
* 2. Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in the
* documentation and/or other materials provided with the distribution.
* 3. The name of the author may not be used to endorse or promote products
* derived from this software without specific prior written permission
*
* THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
* IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
* OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
* IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
* INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
* NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
* DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
* THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
* (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
* THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
*/
/*
* 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
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