195 lines
6.0 KiB
Groff
195 lines
6.0 KiB
Groff
.\" Copyright (c) 1983, 1991, 1993
|
|
.\" The Regents of the University of California. 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. All advertising materials mentioning features or use of this software
|
|
.\" must display the following acknowledgement:
|
|
.\" This product includes software developed by the University of
|
|
.\" California, Berkeley and its contributors.
|
|
.\" 4. Neither the name of the University 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 REGENTS 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 REGENTS 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.
|
|
.\"
|
|
.\" @(#)random.3 8.1 (Berkeley) 6/4/93
|
|
.\"
|
|
.Dd June 4, 1993
|
|
.Dt RANDOM 3
|
|
.Os BSD 4.2
|
|
.Sh NAME
|
|
.Nm random ,
|
|
.Nm srandom ,
|
|
.Nm srandomdev ,
|
|
.Nm initstate ,
|
|
.Nm setstate
|
|
.Nd better random number generator; routines for changing generators
|
|
.Sh SYNOPSIS
|
|
.Fd #include <stdlib.h>
|
|
.Ft long
|
|
.Fn random void
|
|
.Ft void
|
|
.Fn srandom "unsigned long seed"
|
|
.Ft int
|
|
.Fn srandomdev void
|
|
.Ft char *
|
|
.Fn initstate "unsigned long seed" "char *state" "long n"
|
|
.Ft char *
|
|
.Fn setstate "char *state"
|
|
.Sh DESCRIPTION
|
|
The
|
|
.Fn random
|
|
function
|
|
uses a non-linear additive feedback random number generator employing a
|
|
default table of size 31 long integers to return successive pseudo-random
|
|
numbers in the range from 0 to
|
|
.if t 2\u\s731\s10\d\(mi1.
|
|
.if n (2**31)\(mi1.
|
|
The period of this random number generator is very large, approximately
|
|
.if t 16\(mu(2\u\s731\s10\d\(mi1).
|
|
.if n 16*((2**31)\(mi1).
|
|
.Pp
|
|
The
|
|
.Fn random
|
|
and
|
|
.Fn srandom
|
|
functions have (almost) the same calling sequence and initialization properties as the
|
|
.Xr rand 3
|
|
and
|
|
.Xr srand 3
|
|
functions.
|
|
The difference is that
|
|
.Xr rand 3
|
|
produces a much less random sequence \(em in fact, the low dozen bits
|
|
generated by rand go through a cyclic pattern. All the bits generated by
|
|
.Fn random
|
|
are usable. For example,
|
|
.Sq Li random()&01
|
|
will produce a random binary
|
|
value.
|
|
.Pp
|
|
Like
|
|
.Xr rand 3 ,
|
|
.Fn random
|
|
will by default produce a sequence of numbers that can be duplicated
|
|
by calling
|
|
.Fn srandom
|
|
with
|
|
.Ql 1
|
|
as the seed.
|
|
.Pp
|
|
The
|
|
.Fn srandomdev
|
|
routine initialize a state array using
|
|
.Xr urandom 4
|
|
random number device which returns good random numbers,
|
|
suitable for cryptographic use.
|
|
Note that this particular seeding
|
|
procedure can generate states which are impossible to reproduce by
|
|
calling
|
|
.Fn srandom
|
|
with any value, since the succeeding terms in the
|
|
state buffer are no longer derived from the LC algorithm applied to
|
|
a fixed seed.
|
|
If successful
|
|
.Fn srandomdev
|
|
returns 0. It returns -1 on failure, and sets
|
|
.Va errno
|
|
to indicate the error.
|
|
.Pp
|
|
The
|
|
.Fn initstate
|
|
routine allows a state array, passed in as an argument, to be initialized
|
|
for future use. The size of the state array (in bytes) is used by
|
|
.Fn initstate
|
|
to decide how sophisticated a random number generator it should use \(em the
|
|
more state, the better the random numbers will be.
|
|
(Current "optimal" values for the amount of state information are
|
|
8, 32, 64, 128, and 256 bytes; other amounts will be rounded down to
|
|
the nearest known amount. Using less than 8 bytes will cause an error.)
|
|
The seed for the initialization (which specifies a starting point for
|
|
the random number sequence, and provides for restarting at the same
|
|
point) is also an argument.
|
|
The
|
|
.Fn initstate
|
|
function
|
|
returns a pointer to the previous state information array.
|
|
.Pp
|
|
Once a state has been initialized, the
|
|
.Fn setstate
|
|
routine provides for rapid switching between states.
|
|
The
|
|
.Fn setstate
|
|
function
|
|
returns a pointer to the previous state array; its
|
|
argument state array is used for further random number generation
|
|
until the next call to
|
|
.Fn initstate
|
|
or
|
|
.Fn setstate .
|
|
.Pp
|
|
Once a state array has been initialized, it may be restarted at a
|
|
different point either by calling
|
|
.Fn initstate
|
|
(with the desired seed, the state array, and its size) or by calling
|
|
both
|
|
.Fn setstate
|
|
(with the state array) and
|
|
.Fn srandom
|
|
(with the desired seed).
|
|
The advantage of calling both
|
|
.Fn setstate
|
|
and
|
|
.Fn srandom
|
|
is that the size of the state array does not have to be remembered after
|
|
it is initialized.
|
|
.Pp
|
|
With 256 bytes of state information, the period of the random number
|
|
generator is greater than
|
|
.if t 2\u\s769\s10\d,
|
|
.if n 2**69
|
|
which should be sufficient for most purposes.
|
|
.Sh AUTHOR
|
|
Earl T. Cohen
|
|
.Sh DIAGNOSTICS
|
|
If
|
|
.Fn initstate
|
|
is called with less than 8 bytes of state information, or if
|
|
.Fn setstate
|
|
detects that the state information has been garbled, error
|
|
messages are printed on the standard error output.
|
|
.Sh SEE ALSO
|
|
.Xr rand 3 ,
|
|
.Xr srand 3 ,
|
|
.Xr urandom 4
|
|
.Sh HISTORY
|
|
These
|
|
functions appeared in
|
|
.Bx 4.2 .
|
|
.Sh BUGS
|
|
.Pp
|
|
About 2/3 the speed of
|
|
.Xr rand 3 .
|
|
.Pp
|
|
The historical implementation used to have a very weak seeding; the
|
|
random sequence did not vary much with the seed.
|
|
The current implementation employs a better pseudo-random number
|
|
generator for the initial state calculation.
|