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root/Development/ray/src/common/urand.c
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Comparing ray/src/common/urand.c (file contents):
Revision 1.6 by greg, Thu Jul 11 16:25:58 1991 UTC vs.
Revision 1.7 by greg, Mon Aug 12 13:07:02 1991 UTC

# Line 60 | Line 60 | register int  n;
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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