tnfastrand.c - plan9port - [fork] Plan 9 from user space
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       ---
       tnfastrand.c (353B)
       ---
            1 #include <u.h>
            2 #include <libc.h>
            3 #include <libsec.h>
            4 
            5 #define Maxrand        ((1UL<<31)-1)
            6 
            7 ulong
            8 nfastrand(ulong n)
            9 {
           10         ulong m, r;
           11 
           12         /*
           13          * set m to the maximum multiple of n <= 2^31-1
           14          * so we want a random number < m.
           15          */
           16         if(n > Maxrand)
           17                 sysfatal("nfastrand: n too large");
           18 
           19         m = Maxrand - Maxrand % n;
           20         while((r = fastrand()) >= m)
           21                 ;
           22         return r%n;
           23 }