random, srandom, initstate, setstate — random number generator
#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.
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.
|