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RANDOMID(3)                Library Functions Manual                RANDOMID(3)

     randomid randomid_new, randomid_delete, -- provide pseudo-random data
     stream without repetitions

     #include <sys/types.h>
     #include <randomid.h>

     randomid(randomid_t ctx);

     randomid_new(int bits, long timeo);

     randomid_delete(randomid_t ctx);

     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
     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>

                   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


     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 7.1.2                    January 5, 2006                   NetBSD 7.1.2