98 lines
4.1 KiB
ArmAsm
98 lines
4.1 KiB
ArmAsm
/* $NetBSD: random.S,v 1.3 1998/08/15 04:49:50 mycroft Exp $ */
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/*-
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* Copyright (c) 1998 The NetBSD Foundation, Inc.
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* All rights reserved.
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*
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* This code is derived from software contributed to The NetBSD Foundation
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* by Charles M. Hannum.
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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. All advertising materials mentioning features or use of this software
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* must display the following acknowledgement:
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* This product includes software developed by the NetBSD
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* Foundation, Inc. and its contributors.
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* 4. Neither the name of The NetBSD Foundation nor the names of its
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* contributors may be used to endorse or promote products derived
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* from this software without specific prior written permission.
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*
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* THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS
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* ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
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* TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
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* PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS
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* BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
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* CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
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* SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
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* INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
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* CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
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* ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
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* 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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.text
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ENTRY(random)
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movl $16807,%eax
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imull randseed
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shld $1,%eax,%edx
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andl $0x7fffffff,%eax
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addl %edx,%eax
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js 1f
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movl %eax,randseed
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ret
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1:
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subl $0x7fffffff,%eax
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movl %eax,randseed
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ret
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