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From: rjc@uk.ac.ed.cstr (Richard Caley)
Newsgroups: comp.lang.c
Subject: Re: May too many register variables hurt? (was Re: Novice question.)
Message-ID: <RJC.90Nov29012724@brodie.uk.ac.ed.cstr>
Date: 29 Nov 90 01:27:24 GMT
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	<976@mwtech.UUCP> <9733:Nov2722:02:3090@kramden.acf.nyu.edu>
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In-reply-to: brnstnd@kramden.acf.nyu.edu's message of 27 Nov 90 22:02:30 GMT

In article <9733:Nov2722:02:3090@kramden.acf.nyu.edu> brnstnd@kramden.acf.nyu.edu (Dan Bernstein) writes:

    In typical programs, some variables are used quite
    a lot, and they should be declared register. Some variables are rarely
    used, and they shouldn't be declared register. It's better to err on the
    side of extra register declarations than to pessimize your code in the
    common case.

IMHO, it is better not to declare register variabes unless you need to
(i.e. the code won't perform as needed without). Given

	void
	tweakit(register struct foobar *lastone)

	{
	}

vs.

	void
	tweakit(struct foobar *lastone)

	{
	}

I find the second _so_ much more readable that adding in the register
for, say, a 10% speedup in a program which runs in 10 seconds is not
worth it unless you are _very_ sure that that second is critical and
the code is more or less totally stable.

If the time _is_ critical then it is not enough to stick in a few
register variables anyway, it is time to wheel out the profiler, stare
at the assembler output and work out whether floating point arithmetic
or jumps are more time critical on your machine.

--
rjc@uk.ac.ed.cstr	real men don't use typedefs!