RANDOM(3)                            BSD                             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 and srandom have (almost) the same calling sequence and
     initialization properties as rand and srand.  The difference is that
     rand(3) 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(3), 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 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 can 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(3)

BUGS
     About 2/3 the speed of rand(3C).