Path: utzoo!utgpu!water!watmath!clyde!burl!codas!killer!jfh
From: jfh@killer.UUCP (The Beach Bum)
Newsgroups: comp.lang.c
Subject: Re: swap macro -- beware -- oh yeah ?
Summary: Watch closely everyone.
	 I'll only do this once.
Message-ID: <3147@killer.UUCP>
Date: 29 Jan 88 06:49:50 GMT
References: <8801200422.AA19420@decwrl.dec.com> <3061@killer.UUCP> <1182@ark.cs.vu.nl>
Organization: Big "D" Home for Wayward Hackers
Lines: 41

In article <1182@ark.cs.vu.nl>, maart@cs.vu.nl (Maarten Litmaath) writes:
> In article <3061@killer.UUCP> jfh@killer.UUCP (John Haugh) writes:
> \	a ^= b;
> \	b ^= a;
> \	a ^= b;	[ I think this was the code in that article ]
> \
> \What if, A and B are aliases?
> \
> \	let's say, A = B = 7.
> \	after a ^= b, both a and b == 0.
> \	then, after both b ^= a and a ^= b (the second time), a and b
> \	are STILL == 0.
> 
> I think this is not true, you're making a mistake.
> -- 
> Time flies like an arrow, fruit flies |Maarten Litmaath @ Free U Amsterdam:
> like an orange.      (seen elsewhere) |maart@cs.vu.nl, mcvax!botter!ark!maart

I may have missed something in the definition of what an alias is, but in
my book (okay Chris, I won't name names ;-), an alias is a different name
for the same something.  Different name, same storage, person, place,
fruit fly, whatever.

XOR - truth table.

	A	B	O+ (no overprinting here)
	0	0	0
	0	1	1
	1	0	1
	1	1	0

So far so good Maarten?  What if, A and B are aliases?  Well, wipe out
the lines for A != B and what is left in the O+ column? 0.  Now do this for
all those bits.  All 32 or whatever of them.  You get 0.  Lots of times.

- John.
-- 
John F. Haugh II                  SNAIL:  HECI Exploration Co. Inc.
UUCP: ...!ihnp4!killer!jfh                11910 Greenville Ave, Suite 600
"Don't Have an Oil Well? ...              Dallas, TX. 75243
 ... Then Buy One!"                       (214) 231-0993 Ext 260