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root/radiance/ray/src/common/urind.c
Revision: 2.4
Committed: Thu Jul 17 09:21:29 2003 UTC (20 years, 9 months ago) by schorsch
Content type: text/plain
Branch: MAIN
CVS Tags: rad5R4, rad5R2, rad4R2P2, rad5R0, rad5R1, rad3R7P2, rad3R7P1, rad4R2, rad4R1, rad4R0, rad3R6, rad3R6P1, rad3R8, rad3R9, rad4R2P1, rad5R3, HEAD
Changes since 2.3: +2 -1 lines
Log Message: 
Added prototypes and includes from patch by Randolph Fritz.
Added more required includes and reduced other compile warnings.

File Contents

# Content
1 #ifndef lint
2 static const char RCSid[] = "$Id: urind.c,v 2.3 2003/02/25 02:47:22 greg Exp $";
3 #endif
4 /*
5 * Compute pseudo-asyncronous entry point for urand(3)
6 */
7
8 #include "copyright.h"
9 #include "random.h"
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 }