nfastrand.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 }