|RANDOM(3)||Library Functions Manual||RANDOM(3)|
setstate — pseudo-random
number generator; routines for changing generators
int seed, char
To satisfy portable code,
srandomdev() may be called to initialize the
subsystem. In OpenBSD the seed
variable is ignored, and strong random number results will be provided from
arc4random(3). In other
systems, the seed variable primes a simplistic
If the standardized behavior is required
srandom_deterministic() can be substituted for
srandom(), then subsequent
random() calls will return results using the
In non-deterministic (default) mode, the
random() function returns results from
arc4random(3) in the
range from 0 to (2**31)-1.
In deterministic mode, the
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 (2**31)-1. The period of this
random number generator is very large, approximately 16*((2**31)-1), but the
results are a deterministic sequence from the seed.
initstate() routine allows a state
array, passed in as an argument, to be initialized for future use. The size
of the state array (in bytes) is used by
to decide how sophisticated a random number generator it should use —
the more state, the better the random numbers will be. (Current
"optimal" values for the amount of state information 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.) The seed for the
initialization (which specifies a starting point for the random number
sequence, and provides for restarting at the same point) is also an
initstate() function returns a pointer
to the previous state information array.
Once a state has been initialized, the
setstate() routine provides for rapid switching
between states. The
setstate() function returns a
pointer to the previous state array; its argument state array is used for
further random number generation until the next call to
Once a state array has been initialized, it may be restarted at a
different point either by calling
the desired seed, the state array, and its size) or by calling both
setstate() (with the state array) and
srandom() (with the desired seed). The advantage of
srandom() is that the size of the state array does
not have to be remembered after it is initialized.
forces the subsystem into deterministic mode.
initstate() is called with less than 8
bytes of state information, or if
that the state information has been garbled, error messages are printed on
the standard error output.
functions conform to X/Open Portability Guide
Issue 4, Version 2 (“XPG4.2”).
srandom() function does not conform to
X/Open Portability Guide Issue 4, Version 2
srandomdev() function is an
srandom_deterministic() function is an
These functions appeared in 4.2BSD.
Earl T. Cohen
|December 9, 2014||OpenBSD-6.2|