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#ifndef lint |
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static const char RCSid[] = "$Id: urand.c,v 2.13 2022/04/21 02:55:19 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 "rterror.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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static unsigned short empty_tab = 0; |
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|
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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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|
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|
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long |
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irandom( /* better than using random() % modulus */ |
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long modulus |
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) |
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{ |
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if (sizeof(long) >= 8) |
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return((random()*modulus)>>31); |
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|
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if (sizeof(long long) >= 8) |
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return((random()*(long long)modulus)>>31); |
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|
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return(frandom()*modulus); |
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} |
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|
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int |
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initurand( /* initialize urand() for size entries */ |
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int size |
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) |
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{ |
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int order, n; |
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int i, offset; |
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|
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if ((urperm != NULL) & (urperm != &empty_tab)) |
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free((void *)urperm); |
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if (--size <= 0) { |
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empty_tab = 0; |
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urperm = &empty_tab; |
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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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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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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+offset] = urperm[i] <<= 1; |
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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(urmask+1); |
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} |
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|
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|
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int |
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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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{ |
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static int tab[8] = {103699,96289,73771,65203,81119,87037,92051,98899}; |
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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 & 0x7fffffff); |
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} |
