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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

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() and setstate()
       functions return 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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