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root/radiance/ray/src/common/urand.c
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Comparing ray/src/common/urand.c (file contents):
Revision 1.1 by greg, Fri May 17 12:55:27 1991 UTC vs.
Revision 1.6 by greg, Thu Jul 11 16:25:58 1991 UTC

# Line 5 | Line 5 | static char SCCSid[] = "$SunId$ LBL";
5   #endif
6  
7   /*
8 < * Uncorrelated (anticorrelated) random function
8 > * Anticorrelated random function due to Christophe Schlick
9   */
10  
11   #include  "random.h"
# Line 44 | Line 44 | int  size;
44                          else
45                                  urperm[i+offset]++;
46                  }
47 + }
48 +
49 +
50 + int
51 + ilhash(d, n)                    /* hash a set of integer values */
52 + register int  *d;
53 + register int  n;
54 + {
55 +        static int  tab[8] = {13623,353,1637,5831,2314,3887,5832,8737};
56 +        register int  hval;
57 +
58 +        hval = 0;
59 +        while (n-- > 0)
60 +                hval += *d++ * tab[n&7];
61 +        return(hval);
62 + }
63 +
64 +
65 + static char  bctab[256] = {
66 +                0, 1, 1, 2, 1, 2, 2, 3, 1, 2, 2, 3, 2, 3, 3, 4,
67 +                1, 2, 2, 3, 2, 3, 3, 4, 2, 3, 3, 4, 3, 4, 4, 5,
68 +                1, 2, 2, 3, 2, 3, 3, 4, 2, 3, 3, 4, 3, 4, 4, 5,
69 +                2, 3, 3, 4, 3, 4, 4, 5, 3, 4, 4, 5, 4, 5, 5, 6,
70 +                1, 2, 2, 3, 2, 3, 3, 4, 2, 3, 3, 4, 3, 4, 4, 5,
71 +                2, 3, 3, 4, 3, 4, 4, 5, 3, 4, 4, 5, 4, 5, 5, 6,
72 +                2, 3, 3, 4, 3, 4, 4, 5, 3, 4, 4, 5, 4, 5, 5, 6,
73 +                3, 4, 4, 5, 4, 5, 5, 6, 4, 5, 5, 6, 5, 6, 6, 7,
74 +                1, 2, 2, 3, 2, 3, 3, 4, 2, 3, 3, 4, 3, 4, 4, 5,
75 +                2, 3, 3, 4, 3, 4, 4, 5, 3, 4, 4, 5, 4, 5, 5, 6,
76 +                2, 3, 3, 4, 3, 4, 4, 5, 3, 4, 4, 5, 4, 5, 5, 6,
77 +                3, 4, 4, 5, 4, 5, 5, 6, 4, 5, 5, 6, 5, 6, 6, 7,
78 +                2, 3, 3, 4, 3, 4, 4, 5, 3, 4, 4, 5, 4, 5, 5, 6,
79 +                3, 4, 4, 5, 4, 5, 5, 6, 4, 5, 5, 6, 5, 6, 6, 7,
80 +                3, 4, 4, 5, 4, 5, 5, 6, 4, 5, 5, 6, 5, 6, 6, 7,
81 +                4, 5, 5, 6, 5, 6, 6, 7, 5, 6, 6, 7, 6, 7, 7, 8,
82 +        };
83 +
84 +
85 + #define NBITS           32
86 +
87 + #if NBITS==32
88 + #define  bitcount(i)    (bctab[(i)>>24&0xff]+bctab[(i)>>16&0xff]+ \
89 +                                bctab[(i)>>8&0xff]+bctab[(i)&0xff])
90 + #endif
91 + #if  NBITS==16
92 + #define  bitcount(i)    (bctab[(i)>>8&0xff]+bctab[(i)&0xff])
93 + #endif
94 +
95 +
96 + int
97 + urind(s, i)                     /* compute i'th index from seed s */
98 + int     s, i;
99 + {
100 +        register int  ss, k;
101 +        int  left;
102 +
103 +        ss = s*1103515245 + 12345;
104 +        left = 0;
105 +        for (k = i/NBITS; k--; ) {
106 +                left += bitcount(ss);
107 +                ss = ss*1103515245 + 12345;
108 +        }
109 +        for (k = i&(NBITS-1); k--; ss >>= 1)
110 +                left += ss & 1;
111 +        if (ss & 1)
112 +                return(s-left-1);
113 +        return(s-left+i);
114   }

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