random(3)          UNIX System V(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 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


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random(3)          UNIX System V(BSD Compatibility Package)           random(3)


      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)
      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.


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random(3)          UNIX System V(BSD Compatibility Package)           random(3)


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




















































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