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greg |
1.1 |
#ifndef lint |
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greg |
2.11 |
static const char RCSid[] = "$Id: urand.c,v 2.10 2006/04/05 06:22:56 greg Exp $"; |
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greg |
1.1 |
#endif |
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/* |
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greg |
1.5 |
* Anticorrelated random function due to Christophe Schlick |
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greg |
1.1 |
*/ |
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greg |
2.6 |
#include "copyright.h" |
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greg |
2.5 |
|
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schorsch |
2.7 |
#include "standard.h" |
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greg |
1.1 |
#include "random.h" |
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greg |
2.5 |
#undef initurand |
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greg |
1.1 |
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gregl |
2.4 |
#define MAXORDER (8*sizeof(unsigned short)) |
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greg |
2.10 |
static unsigned short empty_tab = 0; |
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unsigned short *urperm = &empty_tab; /* urand() permutation */ |
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int urmask = 0; /* bits used in permutation */ |
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greg |
1.1 |
|
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greg |
2.11 |
|
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gregl |
2.3 |
int |
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greg |
2.11 |
initurand( /* initialize urand() for size entries */ |
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int size |
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) |
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greg |
1.1 |
{ |
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int order, n; |
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greg |
2.11 |
int i, offset; |
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greg |
1.1 |
|
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greg |
2.10 |
if ((urperm != NULL) & (urperm != &empty_tab)) |
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greg |
2.5 |
free((void *)urperm); |
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if (--size <= 0) { |
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greg |
2.10 |
empty_tab = 0; |
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urperm = &empty_tab; |
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greg |
2.5 |
urmask = 0; |
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return(0); |
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} |
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greg |
2.8 |
for (i = 1; (size >>= 1); i++) |
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if (i == MAXORDER) |
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break; |
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order = i; |
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urmask = (1<<order) - 1; |
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gregl |
2.4 |
urperm = (unsigned short *)malloc((urmask+1)*sizeof(unsigned short)); |
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greg |
1.1 |
if (urperm == NULL) { |
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eputs("out of memory in initurand\n"); |
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quit(1); |
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} |
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greg |
2.9 |
urperm[0] = 0; |
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greg |
1.1 |
for (n = 1, offset = 1; n <= order; n++, offset <<= 1) |
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for (i = offset; i--; ) { |
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greg |
2.8 |
urperm[i+offset] = urperm[i] <<= 1; |
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greg |
1.1 |
if (random() & 0x4000) |
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urperm[i]++; |
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else |
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urperm[i+offset]++; |
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} |
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greg |
2.8 |
return(urmask+1); |
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greg |
1.2 |
} |
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int |
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greg |
2.11 |
ilhash( /* hash a set of integer values */ |
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int *d, |
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int n |
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) |
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greg |
1.2 |
{ |
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greg |
2.10 |
static int tab[8] = {103699,96289,73771,65203,81119,87037,92051,98899}; |
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greg |
2.11 |
int hval; |
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greg |
1.2 |
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hval = 0; |
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while (n-- > 0) |
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greg |
2.10 |
hval ^= *d++ * tab[n&7]; |
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return(hval & 0x7fffffff); |
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greg |
1.1 |
} |
