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NAME

       random, srandom, initstate, setstate - random number generator

SYNOPSIS

       #include <stdlib.h>

       long int random(void);

       void srandom(unsigned int seed);

       char *initstate(unsigned int seed, char *state, size_t n);
       char *setstate(char *state);

   Feature Test Macro Requirements for glibc (see feature_test_macros(7)):

       random(), srandom(), initstate(), setstate():
           _SVID_SOURCE || _BSD_SOURCE || _XOPEN_SOURCE >= 500 ||
           _XOPEN_SOURCE && _XOPEN_SOURCE_EXTENDED

DESCRIPTION

       The random() function uses a nonlinear 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 RAND_MAX.   The
       period  of  this  random  number generator is very large, approximately
       16 * ((2^31) - 1).

       The srandom() function sets its argument as the seed for a new sequence
       of  pseudo-random integers to be returned by random().  These sequences
       are repeatable by calling srandom() with the same seed  value.   If  no
       seed  value  is provided, the random() function is automatically seeded
       with a value of 1.

       The initstate() function allows a state array state to  be  initialized
       for  use  by  random().   The  size  of  the  state  array n is used by
       initstate() to decide how sophisticated a random  number  generator  it
       should use -- the larger the state array, the better the random numbers
       will be.  seed is the seed for the initialization,  which  specifies  a
       starting  point  for  the  random  number  sequence,  and  provides for
       restarting at the same point.

       The setstate() function changes the state array used  by  the  random()
       function.   The  state array state is used for random number generation
       until the next call to initstate() or  setstate().   state  must  first
       have  been initialized using initstate() or be the result of a previous
       call of setstate().

RETURN VALUE

       The random() function returns a value  between  0  and  RAND_MAX.   The
       srandom()  function returns no value.  The initstate() function returns
       a pointer to the previous state array.  The setstate() function returns
       a pointer to the previous state array, or NULL on error.

ERRORS

       EINVAL A state array of less than 8 bytes was specified to initstate().

CONFORMING TO

       4.3BSD, POSIX.1-2001.

NOTES

       Current  "optimal"  values for the size of the state array n 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.

       This  function  should  not be used in cases where multiple threads use
       random() and the behavior should be reproducible.  Use random_r(3)  for
       that purpose.

       Random-number  generation  is a complex topic.  Numerical Recipes in C:
       The Art of Scientific Computing (William H. Press, Brian  P.  Flannery,
       Saul   A.   Teukolsky,  William  T.  Vetterling;  New  York:  Cambridge
       University Press, 2007, 3rd ed.)  provides an excellent  discussion  of
       practical   random-number   generation  issues  in  Chapter  7  (Random
       Numbers).

       For a more theoretical discussion  which  also  covers  many  practical
       issues  in  depth,  see Chapter 3 (Random Numbers) in Donald E. Knuth's
       The Art of Computer Programming, volume 2  (Seminumerical  Algorithms),
       2nd  ed.;  Reading,  Massachusetts:  Addison-Wesley Publishing Company,
       1981.

SEE ALSO

       drand48(3), rand(3), random_r(3), srand(3)

COLOPHON

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