NAME
randomid randomid_new,
randomid_delete, —
provide
pseudo-random data stream without repetitions
SYNOPSIS
#include <sys/types.h>
#include <randomid.h>
uint32_t
randomid(
randomid_t
ctx);
randomid_t
randomid_new(
int
bits,
long timeo);
void
randomid_delete(
randomid_t
ctx);
DESCRIPTION
The
randomid() function provides pseudo-random data stream,
which is guaranteed not to generate the same number twice during a certain
duration.
ctx is the context which holds internal state
for the random number generator.
To initialize a context,
randomid_new is used.
bits specifies the bitwidth of the value generated by
randomid(). Currently 32, 20, and 16 are supported.
timeo specifies the reinitialization interval in
seconds.
timeo has to be bigger than
RANDOMID_TIMEO_MIN
.
randomid_new
returns a dynamically-allocated memory region allocated by
malloc(3).
randomid_delete() will
free(3) the internal state
ctx.
The same number may appear after two reinitialization events of the internal
state,
ctx. Reinitialization happens when the random
number generator cycle is exhausted, or
timeo seconds
have passed since the last reinitialization. For instance,
ctx configured to generate 16 bit data stream will
reinitialize its internal state every 30000 calls to
randomid() (or after
timeo seconds),
therefore the same data will not appear until after 30000 calls to
randomid() (or after
timeo seconds).
The internal state,
ctx, determines the data stream
generated by
randomid().
ctx must be
allocated per data stream (such as a specific data field). It must not be
shared among multiple data streams with different usage.
EXAMPLES
#include <stdio.h>
#include <sys/types.h>
#include <randomid.h>
uint32_t
genid(void)
{
static randomid_t ctx = NULL;
if (!ctx)
ctx = randomid_new(16, (long)3600);
return randomid(ctx);
}
ERRORS
randomid_new() returns
NULL
on error
and sets the external variable
errno.
SEE ALSO
arc4random(3)
HISTORY
The pseudo-random data stream generator was designed by Niels Provos for
OpenBSD IPv4 fragment ID generation.
randomid() is a generalized version of the generator,
reworked by Jun-ichiro itojun Hagino, and was introduced in
NetBSD 2.0.