Originální popis anglicky:
random, srandom, initstate, setstate - random number generator
Návod, kniha: Linux Programmer's Manual
#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);
The
random() function uses a non-linear 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().
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.
- EINVAL
- A state array of less than 8 bytes was specified to
initstate().
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.
BSD 4.3
rand(3),
srand(3)
