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From: gof@nosc.ARPA
Newsgroups: net.lang.c
Subject: swap()
Message-ID: <1668@brl-smoke.ARPA>
Date: Wed, 25-Jun-86 18:58:28 EDT
Article-I.D.: brl-smok.1668
Posted: Wed Jun 25 18:58:28 1986
Date-Received: Mon, 30-Jun-86 05:15:18 EDT
Sender: news@brl-smoke.ARPA
Lines: 37


A pair of easy swap(x,y) routines that uses *No* temporary
storage can be seen below:

#define swap(x,y)   (y^=(x^=(y^=x)))

int swap_all(x,y,size)

    char  *x,*y;
    int   size;

{   int   count;
    for (count = 0 ; count < size ;count++)
       swap(x[count],y[count]);
    return(count);
}


It works quickly and, if used with the function, can swap any
size or type data area.  For simple int or long types the macro
will work fine as long as you avoid the usual problems such as
swap(a++,y++)   or anything similar.  A normal call to the
function to swap two arrays might be:

     float  first[100], second[100];
             .
	     .
	     .
     swap_all(first,second,sizeof(first));
             .
	     .
	     

It is a good idea that the sizeof() argument be the smaller of
the two areas to avoid swapping to much data.
---------------------------------------------------------------------
Jerry Fountain  (crash!gof@noscvax.ARPA)