| 1 |
/* Copyright (c) 1991 Regents of the University of California */ |
| 2 |
|
| 3 |
#ifndef lint |
| 4 |
static char SCCSid[] = "$SunId$ LBL"; |
| 5 |
#endif |
| 6 |
|
| 7 |
/* |
| 8 |
* Compute pseudo-asyncronous entry point for urand(3) |
| 9 |
*/ |
| 10 |
|
| 11 |
#define NBITS 32 /* number of bits in an integer */ |
| 12 |
|
| 13 |
static char bctab[256] = { |
| 14 |
0, 1, 1, 2, 1, 2, 2, 3, 1, 2, 2, 3, 2, 3, 3, 4, |
| 15 |
1, 2, 2, 3, 2, 3, 3, 4, 2, 3, 3, 4, 3, 4, 4, 5, |
| 16 |
1, 2, 2, 3, 2, 3, 3, 4, 2, 3, 3, 4, 3, 4, 4, 5, |
| 17 |
2, 3, 3, 4, 3, 4, 4, 5, 3, 4, 4, 5, 4, 5, 5, 6, |
| 18 |
1, 2, 2, 3, 2, 3, 3, 4, 2, 3, 3, 4, 3, 4, 4, 5, |
| 19 |
2, 3, 3, 4, 3, 4, 4, 5, 3, 4, 4, 5, 4, 5, 5, 6, |
| 20 |
2, 3, 3, 4, 3, 4, 4, 5, 3, 4, 4, 5, 4, 5, 5, 6, |
| 21 |
3, 4, 4, 5, 4, 5, 5, 6, 4, 5, 5, 6, 5, 6, 6, 7, |
| 22 |
1, 2, 2, 3, 2, 3, 3, 4, 2, 3, 3, 4, 3, 4, 4, 5, |
| 23 |
2, 3, 3, 4, 3, 4, 4, 5, 3, 4, 4, 5, 4, 5, 5, 6, |
| 24 |
2, 3, 3, 4, 3, 4, 4, 5, 3, 4, 4, 5, 4, 5, 5, 6, |
| 25 |
3, 4, 4, 5, 4, 5, 5, 6, 4, 5, 5, 6, 5, 6, 6, 7, |
| 26 |
2, 3, 3, 4, 3, 4, 4, 5, 3, 4, 4, 5, 4, 5, 5, 6, |
| 27 |
3, 4, 4, 5, 4, 5, 5, 6, 4, 5, 5, 6, 5, 6, 6, 7, |
| 28 |
3, 4, 4, 5, 4, 5, 5, 6, 4, 5, 5, 6, 5, 6, 6, 7, |
| 29 |
4, 5, 5, 6, 5, 6, 6, 7, 5, 6, 6, 7, 6, 7, 7, 8, |
| 30 |
}; |
| 31 |
|
| 32 |
#if NBITS==32 |
| 33 |
#define bitcount(i) (bctab[(i)>>24&0xff]+bctab[(i)>>16&0xff]+ \ |
| 34 |
bctab[(i)>>8&0xff]+bctab[(i)&0xff]) |
| 35 |
#endif |
| 36 |
#if NBITS==16 |
| 37 |
#define bitcount(i) (bctab[(i)>>8&0xff]+bctab[(i)&0xff]) |
| 38 |
#endif |
| 39 |
|
| 40 |
|
| 41 |
int |
| 42 |
urind(s, i) /* compute i'th index from seed s */ |
| 43 |
int s, i; |
| 44 |
{ |
| 45 |
register int ss, k; |
| 46 |
int left; |
| 47 |
|
| 48 |
ss = s*1103515245 + 12345; |
| 49 |
left = 0; |
| 50 |
for (k = i/NBITS; k--; ) { |
| 51 |
left += bitcount(ss); |
| 52 |
ss = ss*1103515245 + 12345; |
| 53 |
} |
| 54 |
for (k = i&(NBITS-1); k--; ss >>= 1) |
| 55 |
left += ss & 1; |
| 56 |
if (ss & 1) |
| 57 |
return(s-left-1); |
| 58 |
return(s-left+i); |
| 59 |
} |
