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RE: Autoconf manual's coverage of signed integer overflow & portability

From: Meissner, Michael
Subject: RE: Autoconf manual's coverage of signed integer overflow & portability
Date: Fri, 12 Jan 2007 17:56:09 -0500

> -----Original Message-----
> I would like to say the one thing I have not heard through this
> discussion is the real reason why the C standards comittee decided
> signed overflow as being undefined.  All I can think of is they were
> thinking of target that do saturation for plus/minus but wrapping for
> multiplications/divide or even targets that trap for some overflow
> (like x86) but not others.

I was on the original C standards committee from its inception through
the ANSI standard in 1989 and the ISO standard in 1990, representing
first Data General, and then the Open Software Foundation.  When the
standard was being produced, we had vendors with one's complement
machines (Univac, and possibly CDC), signed magnitude machines
(Burroughs), word based machines (Univac, Burroughs, Data General,
PR1ME, and a university doing a DEC-10 port).  While these machines are
uncommon now, we did have to keep them in mind while writing the
standard.  Because of the diversity of actual hardware, the only thing
we could say was "don't do that", just like with shifts where the shift
value is not in the proper range (and this bit gcc when I was doing the
early 88k port).

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