random(3)                  DG/UX 4.30                   random(3)



     NAME
          random, srandom, initstate, setstate - better random number
          generator; routines for changing generators

     SYNOPSIS
          long random()

          srandom(seed)
          int seed;

          char *initstate(seed, state, n)
          unsigned seed;
          char *state;
          int n;

          char *setstate(state)
          char *state;

     DESCRIPTION
          Random uses a non-linear additive feedback random number
          generator employing a default table of size 31 long integers
          to return successive pseudo-random numbers in the range from
          0 to (2**31)-1.  The period of this random number generator
          is very large, approximately 16*((2**31)-1).

          Random/srandom have (almost) the same calling sequence and
          initialization properties as rand/srand. The difference is
          that rand(3c) produces a much less random sequence - in
          fact, the low dozen bits generated by rand go through a
          cyclic pattern.  All the bits generated by random are
          usable.  For example, ``random()&01'' will produce a random
          binary value.

          Unlike srand, srandom does not return the old seed; the
          reason for this is that the amount of state information used
          is much more than a single word.  (Two other routines are
          provided to deal with restarting/changing random number
          generators).  Like rand(3c), however, random will by default
          produce a sequence of numbers that can be duplicated by
          calling srandom with 1 as the seed.

          The initstate routine allows a state array, passed in as an
          argument, to be initialized for future use.  The size of the
          state array (in bytes) is used by initstate to decide how
          sophisticated a random number generator it should use -- the
          more state, the better the random numbers will be.  (Current
          "optimal" values for the amount of state information are 8,
          32, 64, 128, and 256 bytes; other amounts will be rounded
          down to the nearest known amount.  Using less than 8 bytes
          will cause an error).  The seed for the initialization
          (which specifies a starting point for the random number
          sequence, and provides for restarting at the same point) is



     Licensed material--property of copyright holder(s)         Page 1

     random(3)                  DG/UX 4.30                   random(3)



          also an argument.  Initstate returns a pointer to the
          previous state information array.

          Once a state has been initialized, the setstate routine
          provides for rapid switching between states.  Setstate
          returns a pointer to the previous state array; its argument
          state array is used for further random number generation
          until the next call to initstate or setstate.

          Once a state array has been initialized, it may be restarted
          at a different point either by calling initstate (with the
          desired seed, the state array, and its size) or by calling
          both setstate (with the state array) and srandom (with the
          desired seed).  The advantage of calling both setstate and
          srandom is that the size of the state array does not have to
          be remembered after it is initialized.

          With 256 bytes of state information, the period of the
          random number generator is greater than 2**69 which should
          be sufficient for most purposes.

     DIAGNOSTICS
          If initstate is called with less than 8 bytes of state
          information, or if setstate detects that the state
          information has been garbled, error messages are printed on
          the standard error output.

     SEE ALSO
          rand(3c)

     CAVEAT
          About 2/3 the speed of rand(3c).























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