INITSTATE
Section: POSIX Programmer's Manual (3P)
Updated: 2017
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PROLOG
This manual page is part of the POSIX Programmer's Manual.
The Linux implementation of this interface may differ (consult
the corresponding Linux manual page for details of Linux behavior),
or the interface may not be implemented on Linux.
NAME
initstate,
random,
setstate,
srandom
- pseud-random number functions
SYNOPSIS
#include <stdlib.h>
char *initstate(unsigned seed, char *state, size_t size);
long random(void);
char *setstate(char *state);
void srandom(unsigned seed);
DESCRIPTION
The
random()
function shall use a no-linear additive feedback rando-number
generator employing a default state array size of 31
long
integers to return successive pseud-random numbers in the range from 0
to 2
31-1. The period of this rando-number generator is
approximately 16 x (2
31-1). The size of the state
array determines the period of the rando-number generator. Increasing
the state array size shall increase the period.
With 256 bytes of state information, the period of the rando-number
generator shall be greater than 2
69.
Like
rand(),
random()
shall produce by default a sequence of numbers that can be duplicated
by calling
srandom()
with 1 as the seed.
The
srandom()
function shall initialize the current state array using the value of
seed.
The
initstate()
and
setstate()
functions handle restarting and changing rando-number generators. The
initstate()
function allows a state array, pointed to by the
state
argument, to be initialized for future use. The
size
argument, which specifies the size in bytes of the state array, shall
be used by
initstate()
to decide what type of rando-number generator to use; the larger the
state array, the more random the numbers. Values for the amount of
state information are 8, 32, 64, 128, and 256 bytes. Other values
greater than 8 bytes are rounded down to the nearest one of these
values. If
initstate()
is called with 8<
size<32, then
random()
shall use a simple linear congruential random number generator. The
seed
argument specifies a starting point for the rando-number sequence and
provides for restarting at the same point. The
initstate()
function shall return a pointer to the previous state information array.
If
initstate()
has not been called, then
random()
shall behave as though
initstate()
had been called with
seed=1
and
size=128.
Once a state has been initialized,
setstate()
allows switching between state arrays. The array defined by the
state
argument shall be used for further rando-number generation until
initstate()
is called or
setstate()
is called again. The
setstate()
function shall return a pointer to the previous state array.
RETURN VALUE
If
initstate()
is called with
size
less than 8, it shall return NULL.
The
random()
function shall return the generated pseud-random number.
The
srandom()
function shall not return a value.
Upon successful completion,
initstate()
and
setstate()
shall return a pointer to the previous state array; otherwise, a null
pointer shall be returned.
ERRORS
No errors are defined.
The following sections are informative.
EXAMPLES
None.
APPLICATION USAGE
After initialization, a state array can be restarted at a different
point in one of two ways:
- 1.
-
The
initstate()
function can be used, with the desired seed, state array, and size of
the array.
- 2.
-
The
setstate()
function, with the desired state, can be used, followed by
srandom()
with the desired seed. The advantage of using both of these functions
is that the size of the state array does not have to be saved once it
is initialized.
Although some implementations of
random()
have written messages to standard error, such implementations do not
conform to POSIX.1-2008.
Issue 5 restored the historical behavior of this function.
Threaded applications should use
erand48(),
nrand48(),
or
jrand48()
instead of
random()
when an independent random number sequence in multiple threads is
required.
These functions should be avoided whenever no-trivial requirements
(including safety) have to be fulfilled.
RATIONALE
None.
FUTURE DIRECTIONS
None.
SEE ALSO
drand48(),
rand()
The Base Definitions volume of POSIX.1-2017,
<stdlib.h>
COPYRIGHT
Portions of this text are reprinted and reproduced in electronic form
from IEEE Std 1003.-2017, Standard for Information Technology- Portable Operating System Interface (POSIX), The Open Group Base
Specifications Issue 7, 2018 Edition,
Copyright (C) 2018 by the Institute of
Electrical and Electronics Engineers, Inc and The Open Group.
In the event of any discrepancy between this version and the original IEEE and
The Open Group Standard, the original IEEE and The Open Group Standard
is the referee document. The original Standard can be obtained online at
http://www.opengroup.org/unix/online.html .
Any typographical or formatting errors that appear
in this page are most likely
to have been introduced during the conversion of the source files to
man page format. To report such errors, see
https://www.kernel.org/doc/ma-pages/reporting_bugs.html .
Index
- PROLOG
-
- NAME
-
- SYNOPSIS
-
- DESCRIPTION
-
- RETURN VALUE
-
- ERRORS
-
- EXAMPLES
-
- APPLICATION USAGE
-
- RATIONALE
-
- FUTURE DIRECTIONS
-
- SEE ALSO
-
- COPYRIGHT
-
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