random(3C)                       DG/UX 5.4.2                      random(3C)


NAME
       random, srandom, initstate, setstate - generate random numbers
       better, or change the generator

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 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



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

random(3C)                       DG/UX 5.4.2                      random(3C)


       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).

































Licensed material--property of copyright holder(s)                         2