Path: utzoo!attcan!uunet!lll-winken!lll-tis!mordor!joyce!sri-unix!garth!smryan
From: smryan@garth.UUCP (Steven Ryan)
Newsgroups: comp.std.c
Subject: Re: the logical xor operator!
Message-ID: <833@garth.UUCP>
Date: 28 Jun 88 20:32:29 GMT
References:  <1719@ogcvax.ogc.edu> <1309@ark.cs.vu.nl> <4772@haddock.ISC.COM> <12178@mimsy.UUCP>
Reply-To: smryan@garth.UUCP (Steven Ryan)
Organization: INTERGRAPH (APD) -- Palo Alto, CA
Lines: 13

The lack of a boolean exclusive-or is probably cultural. Xor is important
for bit fiddling, but few predicates use it. An equivalence operator (even
if it is just a negated xor), on the other hand is useful for boolean but
not bits.

>A good `rule of thumb' is this:
>
>    -------------------------------------------------------------
>    Logical operators are never slower than arithmetic operators.
>    -------------------------------------------------------------
>
>[are there any machines for which this is false?]

Depends how you implement booleans. On a pipelined machine, jumps kill you.