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