60 lines
2.2 KiB
ArmAsm
60 lines
2.2 KiB
ArmAsm
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/* $NetBSD: random.S,v 1.1 1998/02/22 08:43:28 mycroft Exp $ */
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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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ASLOCAL(randseed)
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.long 1
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ENTRY(random)
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movl #16807, d0
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mulsl _ASM_LABEL(randseed), d1:d0
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lsll #1, d0
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roxll #2, d1
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addl d1, d0
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moveql #1, d1
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addxl d1, d0
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lsrl #1, d0
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movl d0, _ASM_LABEL(randseed)
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rts
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