NAME

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


SYNOPSIS

     #include <stdlib.h>

     long random(void)
     void srandom(unsigned seed)
     char *initstate(unsigned seed, char *state, int n)
     char *setstate(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(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 rea-
     son for this is that the amount of state information used is
     much more than a single word.  (Two other routines are  pro-
     vided to deal with restarting/changing random number genera-
     tors).  Like rand(3), however, random will by  default  pro-
     duce 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 previ-
     ous state information array.

     Once a state has been initialized, the setstate routine pro-
     vides  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  ran-
     dom  number  generator is greater than 2**69 which should be
     sufficient for most purposes.


AUTHOR

     Earl T. Cohen


DIAGNOSTICS

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


SEE ALSO

     rand(3).


NOTES

     initstate and setstate are not declared in <stdlib.h>,  pro-
     grammers must provide their own declarations.


BUGS

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