Re: Negative zero denominator

[Sean Conner <sean@...>]

It was thus said that the Great Roberto Ierusalimschy once stated:
> > In other words, just because the machine uses ones' complement doesn't mean
> > there's a negative 0. [...]
> 
> Is there any machine nowadays that use ones' complement?

  I was looking into this a few months ago and my research revealed the
following:

	sign magnitude
		I only found one machine available commercially that used
		sign magnitude, the IBM 7090, released in Nov 1959.  There
		might be more from that era, but I couldn't find any.

	one's compement
		This seemed to be a popular choice for computers in the
		1960s, with the DEC PDP line being perhaps the most well
		known example.  I did find a reference to one machine
		released in the 80s that used one's complement, the CDC
		Cyber 18, which I never heard of (and I've heard of the
		PERC, which had a writable assembly language [1].

	two's complement
		Even DEC switched to two's complement when they came out
		with the VAX line.  And with the exception of the CDC Cyber
		18, I am unaware of any machine made since the early 70s
		that didn't support two's complement.  

		I'm not saying there might not be newer one's complement
		machines made, but I'm not aware of any.

  I think it's safe to assume that today, any CPU designed and made in the
80s or later uses two's complement.

  -spc

[1]	In that you could change the actual instructions on the CPU by
	writing microcode.