Path: utzoo!utgpu!water!watmath!clyde!rutgers!cmcl2!brl-adm!umd5!cvl!mimsy!chris
From: chris@mimsy.UUCP (Chris Torek)
Newsgroups: comp.lang.c
Subject: Re: swap via xor
Message-ID: <10366@mimsy.UUCP>
Date: 28 Jan 88 02:31:13 GMT
References: <8801200422.AA19420@decwrl.dec.com> <3061@killer.UUCP> <1182@ark.cs.vu.nl>
Organization: U of Maryland, Dept. of Computer Science, Coll. Pk., MD 20742
Lines: 16

Let me see if I can lay this to rest.

	a ^= b; b ^= a; a ^= b;

will swap `a' and `b' if the `^' operator can be applied at all.
There is no way within C (short of `#define a b' or equivalent) to
make this fail.  On the other hand,

	*p ^= *q; *q ^= *p; *p ^= *q;

can fail if p==q.  This is what whoever-it-was meant when he said
that the first form could fail if a==b.  He did not mean `if the
values are equal', he meant `if the variables are identical'.
-- 
In-Real-Life: Chris Torek, Univ of MD Comp Sci Dept (+1 301 454 7163)
Domain:	chris@mimsy.umd.edu	Path:	uunet!mimsy!chris