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.\" Part of publib.
.\"
.\" Copyright (c) 1994-2006 Lars Wirzenius. 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.
.\"
.\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``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 AUTHOR 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.
.\"
.\" part of publib
.\" "@(#)publib-strutil:$Id: memshuffle.3,v 1.1.1.1 1994/02/03 17:25:30 liw Exp $"
.\"
.TH MEMSHUFFLE 3 "C Programmer's Manual" Publib "C Programmer's Manual"
.SH NAME
memshuffle \- make an array be in random order
.SH SYNOPSIS
.nf
#include <publib.h>
void *\fBmemshuffle\fR(void *\fIblock\fR, size_t \fIelsize\fR, size_t \fIelnum\fR);
.SH DESCRIPTION
\fImemshuffle\fR will move around the elements of an array in a random
fashion. It uses the standard library function \fIrand\fR(3) to get
the pseudo-random numbers it needs. The caller must set a suitable
seed with \fIsrand\fR(3).
.SH "RETURN VALUE"
\fImemshuffle\fR returns its first argument.
.SH EXAMPLE
To shuffle an integer array one might do the following.
.sp 1
.nf
.in +5
int array[4] = { 1, 2, 3, 4 };
memshuffle(array, sizeof(array[0]), 4);
.in -5
.SH BUGS
On many systems \fIrand\fR(3) is not of very good quality. However,
it is the only random number generator that can be assumed to exist.
Making it possible for the caller to provide an alternate source
of random numbers (e.g., via a function pointer) is perhaps too more
trouble than its worth. A better way would be for everyone to fix
their \fIrand\fR's.
.SH "SEE ALSO"
publib(3), memrev(3), rand(3), srand(3)
.SH AUTHOR
Lars Wirzenius (lars.wirzenius@helsinki.fi)
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