     RANDOM(3)              C LIBRARY FUNCTIONS              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(3V) 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 gen-
          erators).  Like rand(3V), however, random() will by  default
          produce a sequence of numbers that can be duplicated by cal-
          ling 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 informa-
          tion 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  ini-
          tialization (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 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.

     SEE ALSO
          rand(3V)

     EXAMPLES
               /* Initialize and array and pass it in to initstate. */

               static long state1[32] = {
                    3,
                    0x9a319039, 0x32d9c024, 0x9b663182, 0x5da1f342,
                    0x7449e56b, 0xbeb1dbb0, 0xab5c5918, 0x946554fd,
                    0x8c2e680f, 0xeb3d799f, 0xb11ee0b7, 0x2d436b86,
                    0xda672e2a, 0x1588ca88, 0xe369735d, 0x904f35f7,
                    0xd7158fd6, 0x6fa6f051, 0x616e6b96, 0xac94efdc,
                    0xde3b81e0, 0xdf0a6fb5, 0xf103bc02, 0x48f340fb,
                    0x36413f93, 0xc622c298, 0xf5a42ab8, 0x8a88d77b,
                    0xf5ad9d0e, 0x8999220b, 0x27fb47b9
                    };
               main()
               {
                    unsigned seed;
                    int n;

                    seed = 1;
                    n = 128;
                    initstate(seed, (char *) state1, n);
                    setstate(state1);
                    printf("%d0,random());
               }

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

     WARNINGS
          initstate() casts state to (long *), so state must be  long-
          aligned.   If  it is not long-aligned, on some architectures
          the program will dump core.

     BUGS
          random() is only 2/3 as fast as rand(3V).