RAND(3C)             INTERACTIVE UNIX System             RAND(3C)



          NAME
               rand, srand - simple random-number generator

          SYNOPSIS
               int rand ( )

               void srand (seed)
               unsigned seed;

          DESCRIPTION
               The rand function uses a multiplicative congruential
               random-number generator with period 2^32 that returns suc-
               cessive pseudo-random numbers in the range from 0 to
               (2^15)-1.

               The srand function can be called at any time to reset the
               random-number generator to a random starting point.  The
               generator is initially seeded with a value of 1.

          SEE ALSO
               drand48(3C).

          NOTES
               The spectral properties of rand are limited.  The
               drand48(3C) function provides a much better, though more
               elaborate, random-number generator.

               The following functions define the semantics of the func-
               tions rand and srand.

                    static unsigned long int next = 1;
                    int rand()
                    {
                         next = next * 1103515245 + 12345;
                         return ((unsigned int) (next/65536) % 32768);
                    }
                    void srand(seed)
                    unsigned int seed;
                    {
                         next = seed;
                    }

               Specifying the semantics makes it possible to reproduce  the
               behavior of programs that use pseudo-random sequences.  This
               facilitates the testing of  portable  applications  in  dif-
               ferent implementations.









          Rev. C Software Development Set                            Page 1