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From: mojaveg@mojaveg.lsan.sisna.com (Everett M. Greene)
Subject: Re: ONES COMPLEMENT (was: Ada vs Fortran for scientific applications)
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Date: 2006-07-20T08:46:57-08:00
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"Shmuel (Seymour J.) Metz" <spamtrap@library.lspace.org.invalid> writes:
> mojaveg@mojaveg.lsan.sisna.com (Everett M. Greene) said:
> 
> >A subtractive adder.
> 
> How so? 0+(-0) is a straight addition of 0...0 and 7...7, requiring
> no complementation.

Context was deleted so I have no idea what you're trying
to say above.

> >Try the Univac mainframes.
> 
> Which ones? the 490 and the 1107 lines let you test for zero in a
> single instruction.

They test for +0 in one instruction.  If you want to reliably
test for zero, you have to add 0 first.

> >I once got bagged by one of a Univac-designed machine that did 0 x n
> >= -0 for any negative value of n. 
> 
> And that was a problem because?

Because the ensuing test for zero wasn't working reliably.