генератор случайных чисел (random number generator)
Имя (Name)
random, srandom, initstate, setstate - random number generator
Синопсис (Synopsis)
#include <stdlib.h>
long 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():
_XOPEN_SOURCE >= 500
|| /* Glibc since 2.19: */ _DEFAULT_SOURCE
|| /* Glibc <= 2.19: */ _SVID_SOURCE || _BSD_SOURCE
Описание (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 2^31 - 1. 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. 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 results in an error. 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().
Возвращаемое значение (Return value)
The random() function returns a value between 0 and (2^31) - 1.
The srandom() function returns no value.
The initstate() function returns a pointer to the previous state
array. On failure, it returns NULL, and errno is set to indicate
the error.
On success, setstate() returns a pointer to the previous state
array. On failure, it returns NULL, and errno is set to indicate
the error.
Ошибки (Error)
EINVAL The state argument given to setstate() was NULL.
EINVAL A state array of less than 8 bytes was specified to
initstate().
Атрибуты (Attributes)
For an explanation of the terms used in this section, see
attributes(7).
┌──────────────────────────────────────┬───────────────┬─────────┐
│Interface │ Attribute │ Value │
├──────────────────────────────────────┼───────────────┼─────────┤
│random(), srandom(), initstate(), │ Thread safety │ MT-Safe │
│setstate() │ │ │
└──────────────────────────────────────┴───────────────┴─────────┘
Стандарты (Conforming to)
POSIX.1-2001, POSIX.1-2008, 4.3BSD.
Примечание (Note)
The random() function should not be used in multithreaded
programs where reproducible behavior is required. 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.
Ошибки (баги) (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.
Смотри также (See also)
getrandom(2), drand48(3), rand(3), random_r(3), srand(3)
