RANDOM(3)						     Linux Programmer's Manual							 RANDOM(3)

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, approx-
       imately 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  automati-
       cally 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 init-
       state() 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 practi-
       cal 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

       This page is part of release 3.25 of the Linux man-pages project.  A description of the project, and information about reporting bugs,  can
       be found at http://www.kernel.org/doc/man-pages/.

GNU
								    2009-02-03								 RANDOM(3)