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.\" Copyright (c) 1983, 1991 The Regents of the University of California.
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.\" All rights reserved.
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.\"
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.\" Redistribution and use in source and binary forms, with or without
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.\" modification, are permitted provided that the following conditions
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.\" are met:
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.\" 1. Redistributions of source code must retain the above copyright
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.\" notice, this list of conditions and the following disclaimer.
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.\" 2. Redistributions in binary form must reproduce the above copyright
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.\" notice, this list of conditions and the following disclaimer in the
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.\" documentation and/or other materials provided with the distribution.
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.\" 3. Neither the name of the University nor the names of its contributors
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.\" may be used to endorse or promote products derived from this software
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.\" without specific prior written permission.
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
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.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
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.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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.\" SUCH DAMAGE.
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.\"
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.\" $OpenBSD: random.3,v 1.28 2014/12/09 21:55:39 jmc Exp $
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.\"
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.Dd $Mdocdate: December 9 2014 $
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.Dt RANDOM 3
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.Os
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.Sh NAME
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.Nm random ,
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.Nm srandom ,
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.Nm srandom_deterministic ,
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.Nm srandomdev ,
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.Nm initstate ,
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.Nm setstate
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.Nd pseudo-random number generator; routines for changing generators
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.Sh SYNOPSIS
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.In stdlib.h
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.Ft long
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.Fn random void
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.Ft void
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.Fn srandom "unsigned int seed"
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.Ft void
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.Fn srandom_deterministic "unsigned int seed"
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.Ft void
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.Fn srandomdev void
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.Ft char *
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.Fn initstate "unsigned int seed" "char *state" "size_t n"
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.Ft char *
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.Fn setstate "char *state"
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.Sh DESCRIPTION
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.Bf -symbolic
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Standards insist that this interface return deterministic results.
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Unsafe usage is very common, so
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.Ox
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changed the subsystem to return non-deterministic results by default.
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.Ef
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.Pp
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To satisfy portable code,
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.Fn srandom
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or
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.Fn srandomdev
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may be called to initialize the subsystem.
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In
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.Ox
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the
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.Ar seed
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variable is ignored, and strong random number results will be provided from
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.Xr arc4random 3 .
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In other systems, the
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.Ar seed
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variable primes a simplistic deterministic algorithm.
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.Pp
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If the standardized behavior is required
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.Fn srandom_deterministic
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can be substituted for
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.Fn srandom ,
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then subsequent
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.Fn random
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calls will return results using the deterministic algorithm.
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.Pp
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In non-deterministic (default) mode, the
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.Fn random
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function returns results from
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.Xr arc4random 3
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in the range from 0 to (2**31)\-1.
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.Pp
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In deterministic mode, the
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.Fn random
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function uses a non-linear additive feedback random number generator employing
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a default table of size 31 long integers to return successive pseudo-random
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numbers in the range from 0 to (2**31)\-1.
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The period of this random number generator is very large, approximately
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16*((2**31)\-1), but the results are a deterministic sequence from the seed.
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.Pp
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The
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.Fn initstate
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routine allows a state array, passed in as an argument, to be initialized
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for future use.
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The size of the state array (in bytes) is used by
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.Fn initstate
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to decide how sophisticated a random number generator it should use \(em the
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more state, the better the random numbers will be.
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(Current "optimal" values for the amount of state information are
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8, 32, 64, 128, and 256 bytes; other amounts will be rounded down to
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the nearest known amount.
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Using less than 8 bytes will cause an error.)
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The seed for the initialization (which specifies a starting point for
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the random number sequence, and provides for restarting at the same
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point) is also an argument.
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The
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.Fn initstate
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function returns a pointer to the previous state information array.
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.Pp
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Once a state has been initialized, the
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.Fn setstate
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routine provides for rapid switching between states.
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The
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.Fn setstate
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function returns a pointer to the previous state array; its
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argument state array is used for further random number generation
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until the next call to
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.Fn initstate
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or
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.Fn setstate .
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.Pp
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Once a state array has been initialized, it may be restarted at a
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different point either by calling
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.Fn initstate
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(with the desired seed, the state array, and its size) or by calling
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both
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.Fn setstate
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(with the state array) and
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.Fn srandom
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(with the desired seed).
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The advantage of calling both
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.Fn setstate
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and
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.Fn srandom
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is that the size of the state array does not have to be remembered after
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it is initialized.
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.Pp
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Use of
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.Fn srandom_deterministic ,
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.Fn initstate ,
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or
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.Fn setstate
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forces the subsystem into deterministic mode.
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.Sh DIAGNOSTICS
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If
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.Fn initstate
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is called with less than 8 bytes of state information, or if
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.Fn setstate
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detects that the state information has been garbled, error
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messages are printed on the standard error output.
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.Sh SEE ALSO
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.Xr arc4random 3 ,
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.Xr drand48 3 ,
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.Xr rand 3 ,
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.Xr random 4
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.Sh STANDARDS
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The
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.Fn random ,
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.Fn initstate ,
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and
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.Fn setstate
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functions conform to
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.St -xpg4.2 .
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.Pp
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The
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.Fn srandom
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function does not conform to
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.St -xpg4.2 ,
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intentionally.
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.Pp
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The
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.Fn srandomdev
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function is an extension.
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.Pp
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The
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.Fn srandom_deterministic
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function is an
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.Ox
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extension.
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.Sh HISTORY
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These
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functions appeared in
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.Bx 4.2 .
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.Sh AUTHORS
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.An Earl T. Cohen
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