Path: utzoo!utgpu!water!watmath!clyde!ima!haddock!karl
From: karl@haddock.ISC.COM (Karl Heuer)
Newsgroups: comp.lang.c
Subject: Re: Power proposal for ANSI C
Keywords: power exponentiation **
Message-ID: <2252@haddock.ISC.COM>
Date: 14 Jan 88 00:56:49 GMT
References: <38384@sun.uucp>
Reply-To: karl@haddock.ima.isc.com (Karl Heuer)
Organization: Interactive Systems, Boston
Lines: 44

In article <38384@sun.uucp> dgh%dgh@Sun.COM (David Hough) writes:
>Comment #9, Section 3.3.4:  add power operator for integral exponents

As you said, ANSI can pick whatever syntax they want; but to avoid ambiguity
Let's use "*^" when we're just arguing semantics.  I've edited the quoted
material accordingly.

>To best correspond to the usage of mathematics and other computer languages,
>the precedence of *^ must be greater than that of a multiplicative or
>additive operator.

If this were the only criterion, I'd say it should be put into a new
precedence class between unary and multiplicative.  However, this makes -x*^2
mean the "wrong" thing.  If this is a problem (apparently bc users don't
mind), my recommendation is to give it a precedence between postfix unary and
prefix unary.  (Note that "->id", ".id", "[expr]", and "(arglist)" can all be
considered postfix unary, just as "(type)" can be considered prefix unary.)
More precisely:

power-expression:
	postfix-expression
	postfix-expression *^ cast-expression

unary-expression:
	power-expression
	++ unary-expression
	-- unary-expression
	unary-operator cast-expression
	sizeof unary-expression
	sizeof ( type-name )

(Also, "*^=" should be added to the list of assignment operators.)

>Note that unlike other operators, the "usual arithmetic conversions" are not
>made to b and n; the type of the result is always that of b.

I'd like to mention that there is already a precedent: 1<<1L is 2, not 2L.

>If n < 0, then the result is the reciprocal of b *^ (-n), which is 0 if b is
>an integral expression >= 2.

I think 2 *^ -1 should be undefined (as is 1 << -1), rather than zero.

Karl W. Z. Heuer (ima!haddock!karl or karl@haddock.isc.com), The Walking Lint