Newsgroups: comp.arch
Path: utzoo!henry
From: henry@utzoo.uucp (Henry Spencer)
Subject: Re: Shifting question
Message-ID: <1988Jul23.231300.22872@utzoo.uucp>
Organization: U of Toronto Zoology
References: <705@bnr-rsc.UUCP> <11556@steinmetz.ge.com> <1988Jul19.173807.6604@utzoo.uucp> <11606@steinmetz.ge.com>
Date: Sat, 23 Jul 88 23:13:00 GMT

In article <11606@steinmetz.ge.com> davidsen@crdos1.UUCP (bill davidsen) writes:
>  The rules may say anything is undefined, but that doesn't make it a
>good idea. At one time early in standards process, the question of
>having sizes known to the preprocessor was discussed. At that time my
>recollection is that sizeof was not to be allowed in a preprocessor
>constant expression, although reading the standard certainly seems to
>say it is at this time.

You have an out-of-date draft, I believe.  The second-public-comment draft
(I haven't seen the third yet) explicitly forbids sizeof in this context.

>... If C is ever going to be a portable general purpose
>language rather than a toy for hackers, programmers should not have to
>guess that two shifts of 10 don't give the same result as one shift of
>20 (or whatever the sizes may be), or any of the other non-intuitive
>things which happen in the name of speed.

To slightly misquote DMR:  "if you want Pascal, you know where to find it".
C is already a portable general purpose language, one which specializes
in speed rather than in coddling novice C programmers.

Consider an analogy.  Effective and safe use of a fully-equipped vertical
milling machine requires learning and practicing page after page of
procedures and precautions; it is *not* something you can learn in five
minutes, and the machine can -- literally -- kill you if you get sloppy.
Building it out of soft plastic would make it much safer.  However, for
a real machining job, I want the metal one, despite its complex procedures
and the very real dangers incurred in the name of rapid and precise
machining.

>... The default should be to have the source code work as written.

It already does.  When you write >> in a C program, that is the C >>
operator you are writing, not some abstract mathematical version with
different properties.
-- 
Anyone who buys Wisconsin cheese is|  Henry Spencer at U of Toronto Zoology
a traitor to mankind.  --Pournelle |uunet!mnetor!utzoo! henry @zoo.toronto.edu