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IABSD.fr/src/lib/libc/stdlib/rand.3
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.\" Copyright (c) 1990, 1991 The Regents of the University of California. .\" All rights reserved. .\" .\" This code is derived from software contributed to Berkeley by .\" the American National Standards Committee X3, on Information .\" Processing Systems. .\" .\" 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 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. .\" .\" $OpenBSD: rand.3,v 1.21 2022/03/29 18:15:52 naddy Exp $ .\" .Dd $Mdocdate: March 29 2022 $ .Dt RAND 3 .Os .Sh NAME .Nm rand , .Nm rand_r , .Nm srand , .Nm srand_deterministic .Nd bad pseudo-random number generator .Sh SYNOPSIS .In stdlib.h .Ft void .Fn srand "unsigned int seed" .Ft void .Fn srand_deterministic "unsigned int seed" .Ft int .Fn rand void .Ft int .Fn rand_r "unsigned int *seed" .Sh DESCRIPTION .Bf -symbolic Standards insist that this interface return deterministic results. Unsafe usage is very common, so .Ox changed the subsystem to return non-deterministic results by default. .Ef .Pp To satisfy portable code, .Fn srand may be called to initialize the subsystem. In .Ox the .Ar seed variable is ignored, and strong random number results will be provided from .Xr arc4random 3 . In other systems, the .Ar seed variable primes a simplistic deterministic algorithm. .Pp If the standardized behavior is required .Fn srand_deterministic can be substituted for .Fn srand , then subsequent .Fn rand calls will return results using the deterministic algorithm. The deterministic sequence algorithm changed a number of times since original development, is underspecified, and should not be relied upon to remain consistent between platforms and over time. .Pp The .Fn rand function returns a result in the range of 0 to .Dv RAND_MAX . By default, this result comes from .Xr arc4random 3 . If .Fn srand_deterministic was called, the result will be computed using the deterministic algorithm. .Pp The .Fn rand_r function is a thread-safe version of .Fn rand . Storage for the seed must be provided through the .Fa seed argument, and needs to have been initialized by the caller. It always operates using the deterministic algorithm. .Sh SEE ALSO .Xr arc4random 3 , .Xr rand48 3 , .Xr random 3 .Sh STANDARDS The .Fn rand function conforms to .St -ansiC . .Pp The .Fn rand_r function conforms to .St -p1003.1-2008 . .Pp The .Fn srand function does not conform to .St -ansiC , intentionally. .Pp The .Fn srand_deterministic function is an .Ox extension. .Sh HISTORY The functions .Fn rand and .Fn srand first appeared in .At v3 .