RANDOMID(3) Library Functions Manual RANDOMID(3)
randomid randomid_new, randomid_delete, -- provide pseudo-random data
stream without repetitions
randomid_new(int bits, long timeo);
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
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
static randomid_t ctx = NULL;
ctx = randomid_new(16, (long)3600);
randomid_new() returns NULL on error and sets the external variable
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.
NetBSD 6.1.5 January 5, 2006 NetBSD 6.1.5