149 lines
4.1 KiB
Groff
149 lines
4.1 KiB
Groff
|
.\" $NetBSD: randomid.3,v 1.7 2006/01/05 19:45:29 rpaulo Exp $
|
||
|
|
.\"
|
||
|
|
.\" Copyright (C) 2006 The NetBSD Foundation
|
||
|
|
.\" All rights reserved.
|
||
|
|
.\"
|
||
|
|
.\" Copyright (C) 2003 WIDE Project.
|
||
|
|
.\" All rights reserved.
|
||
|
|
.\"
|
||
|
|
.\" Redistribution and use in source and binary forms, with or without
|
||
|
|
.\" modification, are permitted provided that the following conditions
|
||
|
|
.\" are met:
|
||
|
|
.\" 1. Redistributions of source code must retain the above copyright
|
||
|
|
.\" notice, this list of conditions and the following disclaimer.
|
||
|
|
.\" 2. Redistributions in binary form must reproduce the above copyright
|
||
|
|
.\" notice, this list of conditions and the following disclaimer in the
|
||
|
|
.\" documentation and/or other materials provided with the distribution.
|
||
|
|
.\" 3. Neither the name of the project nor the names of its contributors
|
||
|
|
.\" may be used to endorse or promote products derived from this software
|
||
|
|
.\" without specific prior written permission.
|
||
|
|
.\"
|
||
|
|
.\" THIS SOFTWARE IS PROVIDED BY THE PROJECT AND CONTRIBUTORS ``AS IS'' AND
|
||
|
|
.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
|
||
|
|
.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
|
||
|
|
.\" ARE DISCLAIMED. IN NO EVENT SHALL THE PROJECT OR CONTRIBUTORS BE LIABLE
|
||
|
|
.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
|
||
|
|
.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
|
||
|
|
.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
|
||
|
|
.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
|
||
|
|
.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
|
||
|
|
.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
|
||
|
|
.\" SUCH DAMAGE.
|
||
|
|
.\"
|
||
|
|
.Dd January 5, 2006
|
||
|
|
.Dt RANDOMID 3
|
||
|
|
.Os
|
||
|
|
.Sh NAME
|
||
|
|
.Nm randomid
|
||
|
|
.Nm randomid_new ,
|
||
|
|
.Nm randomid_delete ,
|
||
|
|
.Nd provide pseudo-random data stream without repetitions
|
||
|
|
.Sh SYNOPSIS
|
||
|
|
.In sys/types.h
|
||
|
|
.In randomid.h
|
||
|
|
.Ft uint32_t
|
||
|
|
.Fn randomid "randomid_t ctx"
|
||
|
|
.Ft randomid_t
|
||
|
|
.Fn randomid_new "int bits" "long timeo"
|
||
|
|
.Ft void
|
||
|
|
.Fn randomid_delete "randomid_t ctx"
|
||
|
|
.Sh DESCRIPTION
|
||
|
|
The
|
||
|
|
.Fn randomid
|
||
|
|
function provides pseudo-random data stream,
|
||
|
|
which is guaranteed not to generate the same number twice during
|
||
|
|
a certain duration.
|
||
|
|
.Fa ctx
|
||
|
|
is the context which holds internal state for the random number generator.
|
||
|
|
.Pp
|
||
|
|
To initialize a context,
|
||
|
|
.Fa randomid_new
|
||
|
|
is used.
|
||
|
|
.Fa bits
|
||
|
|
specifies the bitwidth of the value generated by
|
||
|
|
.Fn randomid .
|
||
|
|
Currently 32, 20, and 16 are supported.
|
||
|
|
.Fa timeo
|
||
|
|
specifies the reinitialization interval in seconds.
|
||
|
|
.Fa timeo
|
||
|
|
has to be bigger than
|
||
|
|
.Dv RANDOMID_TIMEO_MIN .
|
||
|
|
.Fa randomid_new
|
||
|
|
returns a dynamically-allocated memory region allocated by
|
||
|
|
.Xr malloc 3 .
|
||
|
|
.Pp
|
||
|
|
.Fn randomid_delete
|
||
|
|
will
|
||
|
|
.Xr free 3
|
||
|
|
the internal state
|
||
|
|
.Fa ctx .
|
||
|
|
.Pp
|
||
|
|
The same number may appear after two reinitialization events of the internal state,
|
||
|
|
.Fa ctx .
|
||
|
|
Reinitialization happens when the random number generator cycle is exhausted,
|
||
|
|
or
|
||
|
|
.Fa timeo
|
||
|
|
seconds have passed since the last reinitialization.
|
||
|
|
For instance,
|
||
|
|
.Fa ctx
|
||
|
|
configured to generate 16 bit data stream will reinitialize its internal state
|
||
|
|
every 30000 calls to
|
||
|
|
.Fn randomid
|
||
|
|
.Po
|
||
|
|
or after
|
||
|
|
.Fa timeo
|
||
|
|
seconds
|
||
|
|
.Pc ,
|
||
|
|
therefore the same data will not appear until after 30000 calls to
|
||
|
|
.Fn randomid
|
||
|
|
.Po
|
||
|
|
or after
|
||
|
|
.Fa timeo
|
||
|
|
seconds
|
||
|
|
.Pc .
|
||
|
|
.Pp
|
||
|
|
The internal state,
|
||
|
|
.Fa ctx ,
|
||
|
|
determines the data stream generated by
|
||
|
|
.Fn randomid .
|
||
|
|
.Fa ctx
|
||
|
|
must be allocated per data stream
|
||
|
|
.Pq such as a specific data field .
|
||
|
|
It must not be shared among multiple data streams with different usage.
|
||
|
|
.\"
|
||
|
|
.Sh EXAMPLES
|
||
|
|
.Bd -literal -offset indent
|
||
|
|
#include \*[Lt]stdio.h\*[Gt]
|
||
|
|
#include \*[Lt]sys/types.h\*[Gt]
|
||
|
|
#include \*[Lt]randomid.h\*[Gt]
|
||
|
|
|
||
|
|
uint32_t
|
||
|
|
genid(void)
|
||
|
|
{
|
||
|
|
static randomid_t ctx = NULL;
|
||
|
|
|
||
|
|
if (!ctx)
|
||
|
|
ctx = randomid_new(16, (long)3600);
|
||
|
|
return randomid(ctx);
|
||
|
|
}
|
||
|
|
.Ed
|
||
|
|
.\"
|
||
|
|
.Sh ERRORS
|
||
|
|
.Fn randomid_new
|
||
|
|
returns
|
||
|
|
.Dv NULL
|
||
|
|
on error and sets the external variable
|
||
|
|
.Va errno .
|
||
|
|
.\"
|
||
|
|
.Sh SEE ALSO
|
||
|
|
.Xr arc4random 3
|
||
|
|
.\"
|
||
|
|
.Sh HISTORY
|
||
|
|
The pseudo-random data stream generator was designed by Niels Provos for
|
||
|
|
.Ox
|
||
|
|
IPv4 fragment ID generation.
|
||
|
|
.Fn randomid
|
||
|
|
is a generalized version of the generator, reworked by Jun-ichiro itojun Hagino,
|
||
|
|
and was introduced in
|
||
|
|
.Nx 2.0 .
|