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git-svn-id: svn+ssh://svn.gna.org/svn/gnustep/libs/base/trunk@3496 72102866-910b-0410-8b05-ffd578937521
112 lines
2.8 KiB
Objective-C
112 lines
2.8 KiB
Objective-C
/* Implementation additive congruential pseudo-random num generating
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Copyright (C) 1994, 1995, 1996 Free Software Foundation, Inc.
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Written by: Andrew Kachites McCallum <mccallum@gnu.ai.mit.edu>
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Date: July 1994
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This file is part of the GNUstep Base Library.
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This library is free software; you can redistribute it and/or
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modify it under the terms of the GNU Library General Public
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License as published by the Free Software Foundation; either
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version 2 of the License, or (at your option) any later version.
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This library is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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Library General Public License for more details.
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You should have received a copy of the GNU Library General Public
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License along with this library; if not, write to the Free
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Software Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
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*/
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#include <config.h>
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#include <base/RNGAdditiveCongruential.h>
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#include <base/Coder.h>
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#include <limits.h>
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/* Additive Congruential Method,
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from Robert Sedgewick, "Algorithms" */
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/* The Chi^2 test results for this RNG is bad.
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xxx Find the bug. */
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@implementation RNGAdditiveCongruential
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- initWithTableSize: (int)s tapsAtOffsets: (int)t1 :(int)t2
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{
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[super init];
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table_size = s;
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tap1 = t1;
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tap2 = t2;
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OBJC_MALLOC(table, long, table_size);
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[self setRandomSeed:0];
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return self;
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}
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- (void) encodeWithCoder: anEncoder
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{
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[self notImplemented:_cmd];
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}
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- initWithCoder: aDecoder
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{
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[self notImplemented:_cmd];
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return self;
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}
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- (void) dealloc
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{
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OBJC_FREE(table);
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[super dealloc];
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}
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- init
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{
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[self initWithTableSize:55 tapsAtOffsets:31 :55];
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return self;
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}
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#define BITS_PER_CHAR 8
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#define HIGH_BYTE(X) ((X) / (1 << (sizeof(X)-1) * BITS_PER_CHAR))
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- (long) nextRandom
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{
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int i;
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long result = 0;
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/* Grab only the high bytes---they are the most random */
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for (i = 0; i < sizeof(long); i++)
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{
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index = (index + 1) % table_size;
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table[index] = (table[(index + table_size - tap1) % table_size]
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+
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table[(index + table_size - tap2) % table_size]);
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result = (result << BITS_PER_CHAR) + HIGH_BYTE(table[index]);
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}
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return result;
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}
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- (void) setRandomSeed: (long)s
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{
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/* Fill the table with the linear congruential method,
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from Robert Sedgewick, "Algorithms" */
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/* b must be x21, with x even, one less number of digits than ULONG_MAX */
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unsigned long b = ((ULONG_MAX / 1000) * 200) + 21;
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unsigned char *byte_table = (unsigned char*) table;
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int byte_table_size = table_size * sizeof(*table);
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int i;
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for (i = 0; i < byte_table_size; i++)
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{
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s = s * b + 1;
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byte_table[i] = HIGH_BYTE(s);
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}
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/* Reset index to beginning */
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index = 0;
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return;
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}
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@end
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