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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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| 49 |
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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| 52 |
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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| 67 |
greg |
1.2 |
{
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| 68 |
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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| 70 |
greg |
1.2 |
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| 71 |
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hval = 0;
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while (n-- > 0)
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| 73 |
greg |
2.10 |
hval ^= *d++ * tab[n&7];
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return(hval & 0x7fffffff);
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| 75 |
greg |
1.1 |
}
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