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From: jsdy@hadron.UUCP (Joseph S. D. Yao)
Newsgroups: net.lang.c
Subject: Re: C "optimization"
Message-ID: <85@hadron.UUCP>
Date: Wed, 20-Nov-85 15:25:05 EST
Article-I.D.: hadron.85
Posted: Wed Nov 20 15:25:05 1985
Date-Received: Sat, 23-Nov-85 09:52:59 EST
References: <2539@sjuvax.UUCP>
Reply-To: jsdy@hadron.UUCP (Joseph S. D. Yao)
Distribution: net
Organization: Hadron, Inc., Fairfax, VA
Lines: 25
Summary: Mindless optimisation sometimes hurts.

One of the original purposes of the C compiler was to compile
a then-obscure operating system on the PDP-7 and PDP-11.  In
device drivers for this OS, some routines read like:
	send(c)
	{
		LPADDR->word = WRITE | GO;
		LPADDR->word = c;
		c = LPADDR->word;
		return(c);
	}
or words to that effect.  I would get quite upset if optimising
this led to:
	send(c)
	{
		return(LPADDR->word = c);
	}
Remember, this was before we had implemented compilers with the
"const" and "var" keywords.  (Oh, you mean it's still before?
Re-calibrate that wayback, would you, Sherman?)

I think my memory on that other keyword is wrong, but I'll post
this anyway for the general content.
-- 

	Joe Yao		hadron!jsdy@seismo.{CSS.GOV,ARPA,UUCP}