randomid(3) - NetBSD Manual Pages

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RANDOMID(3)             NetBSD 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 num-
     ber 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 dif-
     ferent 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 intro-
     duced in NetBSD 2.0.

NetBSD 10.99                    January 5, 2006                   NetBSD 10.99