105 lines
4.1 KiB
ArmAsm
105 lines
4.1 KiB
ArmAsm
/* $NetBSD: random.S,v 1.4 2007/01/14 13:26:18 ragge Exp $ */
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/*
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* Copyright (c) 1994 Ludd, University of Lule}, Sweden. All rights reserved.
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*
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* Redistribution and use in source and binary forms, with or without
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* modification, are permitted provided that the following conditions
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* are met:
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* 1. Redistributions of source code must retain the above copyright
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* notice, this list of conditions and the following disclaimer.
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* 2. Redistributions in binary form must reproduce the above copyright
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* notice, this list of conditions and the following disclaimer in the
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* documentation and/or other materials provided with the distribution.
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* 3. The name of the author may not be used to endorse or promote products
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* derived from this software without specific prior written permission
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*
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* THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
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* IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
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* OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
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* IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
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* INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
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* NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
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* DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
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* THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
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* (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
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* THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
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*/
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/*
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* Copyright (c) 1990,1993 The Regents of the University of California.
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* All rights reserved.
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*
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* Redistribution and use in source and binary forms, with or without
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* modification, are permitted provided that: (1) source code distributions
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* retain the above copyright notice and this paragraph in its entirety, (2)
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* distributions including binary code include the above copyright notice and
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* this paragraph in its entirety in the documentation or other materials
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* provided with the distribution, and (3) all advertising materials mentioning
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* features or use of this software display the following acknowledgement:
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* ``This product includes software developed by the University of California,
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* Lawrence Berkeley Laboratory and its contributors.'' Neither the name of
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* the University nor the names of its contributors may be used to endorse
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* or promote products derived from this software without specific prior
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* written permission.
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* THIS SOFTWARE IS PROVIDED ``AS IS'' AND WITHOUT ANY EXPRESS OR IMPLIED
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* WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED WARRANTIES OF
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* MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE.
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*
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* Here is a very good random number generator. This implementation is
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* based on ``Two Fast Implementations of the "Minimal Standard" Random
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* Number Generator'', David G. Carta, Communications of the ACM, Jan 1990,
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* Vol 33 No 1. Do NOT modify this code unless you have a very thorough
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* understanding of the algorithm. It's trickier than you think. If
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* you do change it, make sure that its 10,000'th invocation returns
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* 1043618065.
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*
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* Here is easier-to-decipher pseudocode:
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*
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* p = (16807*seed)<30:0> # e.g., the low 31 bits of the product
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* q = (16807*seed)<62:31> # e.g., the high 31 bits starting at bit 32
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* if (p + q < 2^31)
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* seed = p + q
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* else
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* seed = ((p + q) & (2^31 - 1)) + 1
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* return (seed);
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*
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* The result is in (0,2^31), e.g., it's always positive.
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*/
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#include <machine/asm.h>
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.data
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randseed:
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.long 1
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ENTRY(random, 0)
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movl $16807,%r0
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movl randseed,%r1 # %r2=16807*loword(randseed)
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bicl3 $0xffff0000,%r1,%r2
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mull2 %r0,%r2
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ashl $-16,%r1,%r1 # %r1=16807*hiword(randseed)
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bicl2 $0xffff0000,%r1
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mull2 %r0,%r1
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bicl3 $0xffff0000,%r2,%r0
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ashl $-16,%r2,%r2 # %r1+=(%r2>>16)
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bicl2 $0xffff0000,%r2
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addl2 %r2,%r1
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ashl $16,%r1,%r2 # %r0|=%r1<<16
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bisl2 %r2,%r0
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ashl $-16,%r1,%r1 # %r1=%r1>>16
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ashl $1,%r1,%r1
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movl %r0,%r2
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rotl $1,%r0,%r0
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bicl2 $0xfffffffe,%r0
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bisl2 %r0,%r1
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movl %r2,%r0
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bicl2 $0x80000000,%r0
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addl2 %r1,%r0
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bgeq L1
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subl2 $0x7fffffff,%r0
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L1: movl %r0,randseed
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ret
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