RANDOMID(3) BSD Library Functions Manual RANDOMID(3)
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 dura-
tion. 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.
BSD
January 5, 2006 BSD
