random(3)               (BSD Compatibility Package)               random(3)


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

   SYNOPSIS
         cc [ flag... ] file ... -lucb

         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 [see rand(3C)].  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 because 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.  n specifies the size of state in
         bytes.  initstate uses n 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


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   random(3)               (BSD Compatibility Package)               random(3)


         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 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.

   EXAMPLE
               /* Initialize an 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, state1, n);
                     setstate(state1);
                     printf("%d0,random());
               }

   SEE ALSO
         rand(3C).





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   random(3)               (BSD Compatibility Package)               random(3)


         drand48(2), drand(3C), rand(3C), srand(3C) in the Programmer's
         Reference Manual.

   RETURN VALUE
         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.

   NOTES
         About two-thirds the speed of rand(3C).











































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