man(1) Manual page archive

     RAND(2)                                                   RAND(2)

          rand, lrand, frand, nrand, lnrand, srand, truerand,
          n_truerand, fastrand - random number generator

          #include <u.h>
          #include <libc.h>

          int    rand(void)

          long   lrand(void)

          double frand(void)

          int    nrand(int val)

          long   lnrand(long val)

          void   srand(long seed)

          ulong  truerand(void)

          int    n_truerand(int val)

          ulong  fastrand(void)

          Rand returns a uniform pseudo-random number x, 0≤x<215.

          Lrand returns a uniform long x, 0≤x<231.

          Frand returns a uniform double x, 0.0≤x<1.0, This function
          calls lrand twice to generate a number with as many as 62
          significant bits of mantissa.

          Nrand returns a uniform integer x, 0≤x<val.  Lnrand is the
          same, but returns a long.

          The algorithm is additive feedback with:

               x[n] = (x[n-273] + x[n-607]) mod 2^31

          giving a period of 2^30 × (2^607 - 1).

          The generators are initialized by calling srand with what-
          ever you like as argument.  To get a different starting
          value each time,


     RAND(2)                                                   RAND(2)

          will work as long as it is not called more often than once
          per second.  Calling


          will initialize the generators to their starting state.

          Truerand returns a random unsigned long read from
          /dev/random.  Due to the nature of /dev/random, truerand can
          only return a few hundred bits a second.

          N_truerand returns a uniform integer x, 0≤x<val.

          Fastrand is a pseudo random number generator which is seeded
          and periodically scrambled using truerand. It is approxi-
          mately 1000 times faster than truerand and is intended for
          security software that requires a larger stream of unguess-
          able data.