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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 useā€”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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