two's complement, was Re: Now OT

Al Kossow aek at
Thu Jun 23 11:07:40 CDT 2016

On 6/23/16 8:17 AM, Chuck Guzis wrote:
> On 06/23/2016 07:31 AM, Paul Koning wrote:
>> I have a copy of 1948 (!) lecture notes on computer design.  It
>> discusses one's complement and two's complement.  It points out the
>> advantage of two's complement (no two zeroes) but also the
>> disadvantage that negating is harder (requiring two steps).  In early
>> computers that was significant, which explains why you see one's
>> complement there.
> There are also a few obscure bit-twiddling tricks that work in ones
> complement, but not in two's.

I have also heard that 2s compliment was popular in shorter word length
machines because 1s compliment multiple precision arithmetic is a PITA
to implement.

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