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.\"   Copyright (c) 1994-2006 Lars Wirzenius.  All rights reserved.
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.\" part of publib
.\" "@(#)publib-strutil:$Id: memshuffle.3,v 1.1.1.1 1994/02/03 17:25:30 liw Exp $"
.\"
.TH MEMSHUFFLE 3pub "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)