Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!samsung!munnari.oz.au!metro!wolfen!hls0!george
From: george@hls0.hls.oz (George Turczynski)
Newsgroups: comp.lang.c
Subject: Re: Help!!!!
Message-ID: <937@hls0.hls.oz>
Date: 25 Sep 90 23:13:41 GMT
References: <26f8528c.35c1@uop.uop.edu> <1990Sep21.182142.9013@everexn.com>
Lines: 29

In article <1990Sep21.182142.9013@everexn.com>, roger@everexn.com (Roger House) writes:

	[...Deleted...]
> 
> Say B is the variable for which bits 2 and 5 are to be swapped.  Then this 
> code will do the trick, although it requires the use of another variable, 
> t:
> 
> 	if ((t = B & 0x24) && t != 0x24)      /* Swap bits 2 and 5 of B */
> 		B ^= 0x24;
> 
> There are probably better ways to do it.
> 

Well, to do a similar thing without the use of a temporary, try
this:

	B= !!(B&0x20)^!!(B&0x4) ? B^0x24 : B;

This follows from your truth table (that I deleted), as the result
is only different if bits 5 and 2 are different (which is what the
curious looking test, !!(B&0x20)^!!(B&0x4), finds out).

-- 
George P. J. Turczynski,   Computer Systems Engineer. Highland Logic Pty Ltd.
ACSnet: george@highland.oz |^^^^^^^^^^^^^^^^^^^^^^^^| Suite 1, 348-354 Argyle St
Phone:  +61 48 683490      |  Witty remarks are as  | Moss Vale, NSW. 2577
Fax:    +61 48 683474      |  hard to come by as is | Australia.
---------------------------   space to put them !    ---------------------------