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From: "robin" <robin_v@bigpond.com>
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 <44bceab6$29$fuzhry+tra$mr2ice@news.patriot.net>
Subject: Re: ONES COMPLEMENT
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Message-ID: <MDqvg.7681$tE5.7262@news-server.bigpond.net.au>
Date: Wed, 19 Jul 2006 13:41:00 GMT
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Date: 2006-07-19T13:41:00+00:00
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Shmuel (Seymour J.) Metz wrote in message <44bceab6$29$fuzhry+tra$mr2ice@news.patriot.net>...
>In <20060717.7A4ADD0.10B1A@mojaveg.lsan.sisna.com>, on 07/17/2006
>   at 06:26 PM, mojaveg@mojaveg.lsan.sisna.com (Everett M. Greene)
>said:
>
>>"robin" <robin_v@bigpond.com> writes:
>
>>> Some implementations of ones complement used two forms of
>>> zero
>
>FSVO "some" equal to "all".

Not all.

>>>which required two tests.
>
>That  makes no sense.

One test for all bits zero, the other required for all ones.

>>A properly designed 1s complement machine would not
>>generate -0 in normal arithmetic operations.
>
>0+(-0)?
>
>>Thus, no need to perform a program check for -0.
>
>I never saw a need to test for it regardless. Every 1s complement
>machine I know of lets you test for zero in a single instruction.

(-0) looked like a negative value on some machines.

>>> How many machines now offer ones complement arithmetic?
>
>Before the S/360 captured the market there were large numbers of
>machines in the lines started with the CDC 160, CDC 6660 and the
>UNIVAC 1107. The shift seemed to be a copycat issue more than a
>technological one.