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greg |
1.1 |
#ifndef lint |
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greg |
2.2 |
static const char RCSid[] = "$Id$"; |
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greg |
1.1 |
#endif |
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/* |
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* Compute pseudo-asyncronous entry point for urand(3) |
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greg |
2.2 |
*/ |
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greg |
2.3 |
#include "copyright.h" |
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greg |
1.1 |
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#define NBITS 32 /* number of bits in an integer */ |
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static char bctab[256] = { |
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0, 1, 1, 2, 1, 2, 2, 3, 1, 2, 2, 3, 2, 3, 3, 4, |
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1, 2, 2, 3, 2, 3, 3, 4, 2, 3, 3, 4, 3, 4, 4, 5, |
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1, 2, 2, 3, 2, 3, 3, 4, 2, 3, 3, 4, 3, 4, 4, 5, |
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2, 3, 3, 4, 3, 4, 4, 5, 3, 4, 4, 5, 4, 5, 5, 6, |
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1, 2, 2, 3, 2, 3, 3, 4, 2, 3, 3, 4, 3, 4, 4, 5, |
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2, 3, 3, 4, 3, 4, 4, 5, 3, 4, 4, 5, 4, 5, 5, 6, |
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2, 3, 3, 4, 3, 4, 4, 5, 3, 4, 4, 5, 4, 5, 5, 6, |
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3, 4, 4, 5, 4, 5, 5, 6, 4, 5, 5, 6, 5, 6, 6, 7, |
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1, 2, 2, 3, 2, 3, 3, 4, 2, 3, 3, 4, 3, 4, 4, 5, |
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2, 3, 3, 4, 3, 4, 4, 5, 3, 4, 4, 5, 4, 5, 5, 6, |
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2, 3, 3, 4, 3, 4, 4, 5, 3, 4, 4, 5, 4, 5, 5, 6, |
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3, 4, 4, 5, 4, 5, 5, 6, 4, 5, 5, 6, 5, 6, 6, 7, |
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2, 3, 3, 4, 3, 4, 4, 5, 3, 4, 4, 5, 4, 5, 5, 6, |
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3, 4, 4, 5, 4, 5, 5, 6, 4, 5, 5, 6, 5, 6, 6, 7, |
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3, 4, 4, 5, 4, 5, 5, 6, 4, 5, 5, 6, 5, 6, 6, 7, |
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4, 5, 5, 6, 5, 6, 6, 7, 5, 6, 6, 7, 6, 7, 7, 8, |
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}; |
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#if NBITS==32 |
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#define bitcount(i) (bctab[(i)>>24&0xff]+bctab[(i)>>16&0xff]+ \ |
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bctab[(i)>>8&0xff]+bctab[(i)&0xff]) |
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#endif |
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#if NBITS==16 |
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#define bitcount(i) (bctab[(i)>>8&0xff]+bctab[(i)&0xff]) |
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#endif |
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int |
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urind(s, i) /* compute i'th index from seed s */ |
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int s, i; |
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{ |
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register int ss, k; |
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int left; |
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ss = s*1103515245 + 12345; |
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left = 0; |
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for (k = i/NBITS; k--; ) { |
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left += bitcount(ss); |
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ss = ss*1103515245 + 12345; |
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} |
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for (k = i&(NBITS-1); k--; ss >>= 1) |
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left += ss & 1; |
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if (ss & 1) |
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return(s-left-1); |
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return(s-left+i); |
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} |
