RANDOMID(3) | Library Functions Manual | RANDOMID(3) |
randomid
, randomid_new
,
randomid_delete
—
#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);
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.
#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); }
randomid_new
() returns NULL
on
error and sets the external variable errno.
randomid
() is a generalized version of the generator,
reworked by Jun-ichiro itojun Hagino, and was introduced in
NetBSD 2.0.
January 5, 2006 | NetBSD 9.0 |