netbsd man page for randomid

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