RANDOMID(3) BSD Library Functions Manual RANDOMID(3)
randomid randomid_new, randomid_delete, -- provide pseudo-random data stream without repeti-
randomid_new(int bits, long timeo);
The randomid() function provides pseudo-random data stream, which is guaranteed not to gen-
erate 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 sec-
onds 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 mul-
tiple data streams with different usage.
static randomid_t ctx = NULL;
ctx = randomid_new(16, (long)3600);
randomid_new() returns NULL on error and sets the external variable errno.
The pseudo-random data stream generator was designed by Niels Provos for OpenBSD IPv4 frag-
ment ID generation. randomid() is a generalized version of the generator, reworked by Jun-
ichiro itojun Hagino, and was introduced in NetBSD 2.0.
BSD January 5, 2006 BSD