Path: utzoo!utgpu!water!watmath!clyde!rutgers!rochester!cornell!uw-beaver!uw-june!pardo
From: pardo@uw-june.UUCP (David Keppel)
Newsgroups: comp.lang.c
Subject: Re: parens honored
Keywords: ANSI C standard parens pragmas efficiency
Message-ID: <3959@uw-june.UUCP>
Date: 11 Jan 88 01:03:56 GMT
References: <6829@brl-smoke.ARPA> <2845@zeus.TEK.COM> <6860@brl-smoke.ARPA> <7009@brl-smoke.ARPA> <7563@elsie.UUCP>
Reply-To: pardo@uw-june.UUCP (David Keppel)
Organization: U of Washington, Computer Science, Seattle
Lines: 25

[ if you want to force evaluation order use temporaries ]

3 thoughts about this:

(1) Super-optimizing compilers may get rid of the temporaries.

(2) You can't always (easily) use temporaries when using macros.

(3) Under ANSI-C, parens can be reordered as long as there isn't potential
    for overflow.  To be able to exploit this effectively (to be able to
    freely rearrange parens almost everywhere, which is what you want),
    you need to be able to declare variables as being range-restricted:

	#define	BUFSIZE 256
	typedef /* some type goes here */ a_type;
	a_type	pragma(range 0..BUFSIZE) i, j, k, l;

    so that

	    i = j + (k - l);

    can be freely rearranged if a_type is 16 bits (or even unsigned 9),
    but not if it is 8 bits.

	;-D on  (Ada(TM) is NOT a trademark of dpANS!)  Pardo