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#ifndef lint |
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static const char RCSid[] = "$Id: urand.c,v 2.6 2003/02/25 02:47:22 greg Exp $"; |
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#endif |
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/* |
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* Anticorrelated random function due to Christophe Schlick |
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*/ |
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|
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#include "copyright.h" |
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|
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#include <stdlib.h> |
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|
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#include "standard.h" |
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#include "random.h" |
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|
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#undef initurand |
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|
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#define MAXORDER (8*sizeof(unsigned short)) |
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|
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unsigned short *urperm = NULL; /* urand() permutation */ |
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int urmask; /* bits used in permutation */ |
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|
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int |
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initurand(size) /* initialize urand() for size entries */ |
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int size; |
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{ |
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int order, n; |
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register int i, offset; |
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|
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if (urperm != NULL) |
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free((void *)urperm); |
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if (--size <= 0) { |
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urperm = NULL; |
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urmask = 0; |
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return(0); |
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} |
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for (i = 1; size >>= 1; i++) |
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; |
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order = i>MAXORDER ? MAXORDER : i; |
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urmask = (1<<i) - 1; |
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urperm = (unsigned short *)malloc((urmask+1)*sizeof(unsigned short)); |
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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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urperm[0] = 0; |
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for (n = 1, offset = 1; n <= order; n++, offset <<= 1) |
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for (i = offset; i--; ) { |
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urperm[i] = |
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urperm[i+offset] = 2*urperm[i]; |
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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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return(1<<order); |
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} |
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|
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|
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int |
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ilhash(d, n) /* hash a set of integer values */ |
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register int *d; |
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register int n; |
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{ |
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static int tab[8] = {13623,353,1637,5831,2314,3887,5832,8737}; |
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register int hval; |
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|
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hval = 0; |
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while (n-- > 0) |
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hval += *d++ * tab[n&7]; |
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return(hval); |
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} |
