Path: utzoo!attcan!uunet!van-bc!sl
From: sl@van-bc.UUCP (pri=-10 Stuart Lynne)
Newsgroups: comp.unix.questions
Subject: Re: Bit Switching - How?
Keywords: bits, flip
Message-ID: <2345@van-bc.UUCP>
Date: 5 Apr 89 00:27:30 GMT
References: <1138@uvm-gen.UUCP> <9977@smoke.BRL.MIL>
Reply-To: sl@van-bc.UUCP (pri=-10 Stuart Lynne)
Organization: Wimsey Associates, Vancouver, BC.
Lines: 19

In article <1138@uvm-gen.UUCP> wirthlin@uvm-gen.UUCP (Ralph Wirthlin) writes:
>Does anyone know of a *very fast* way to swap bits at some location n 
>between two separate bytes b1 and b2?

For fast generic swapping I use:

#define	swap(a,b) {a^=b;b^=a;a^= b;}

This method has the advantage of not needing any temporary variable. So if
your arg's are in registers it reduces to three XOR instructions.

Be sure to implement as a macro, procedure call overhead would dwarf
everything else if you didn't.

Adding masks so that it only handles bits is left as an exercise for the 
reader :-)

-- 
Stuart.Lynne@wimsey.bc.ca uunet!van-bc!sl 604-937-7532(voice) 604-939-4768(fax)