#### 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.
On error, __errno__ is set to indicate the cause.
On success, setstate() returns a pointer to the previous state array.
On error, it returns NULL, with __errno__ set to indicate the cause of the
error.
#### ERRORS
EINVAL The __state__ argument given to setstate() was NULL.
EINVAL A state array of less than 8 bytes was specified to initstate().
#### ATTRIBUTES
Multithreading (see pthreads(7))
The random(), srandom(), initstate(), and setstate() functions are
thread-safe.
#### 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.
#### BUGS
According to POSIX, initstate() should return NULL on error. In the
glibc implementation, __errno__ is (as specified) set on error, but the
function does not return NULL.
#### SEE ALSO
drand48(3), rand(3), random_r(3), srand(3)
#### COLOPHON
This page is part of release 3.65 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/.
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