Exact integer-valued floats

[wrw at mac.com]

On Sep 22, 2012, at 7:06 PM, Dave Angel <d at davea.name> wrote:

> On 09/22/2012 05:05 PM, Tim Roberts wrote:
>> Dennis Lee Bieber <wlfraed at ix.netcom.com> wrote:
>>> On 22 Sep 2012 01:36:59 GMT, Steven D'Aprano wrote:
>>>> For non IEEE 754 floating point systems, there is no telling how bad the 
>>>> implementation could be :(
>>> 	Let's see what can be found...
>>> 
>>> 	IBM 360: Same as Sigma-6 (no surprise; hearsay is the Sigma was
>>> designed by renegade IBM folk; even down to using EBCDIC internally --
>>> but with a much different interrupt system [224 individual interrupt
>>> vectors as I recall, vs the IBM's 7 vectors and polling to find what
>>> device]).
>> The Control Data 6000/Cyber series had sign bit and 11-bit exponent, with
>> either a 48-bit mantissa or a 96-bit mantissa, packed into one or two
>> 60-bit words.  Values were not automatically normalized, so there was no
>> assumed 1 bit, as in IEEE-754.
> 
> And it's been a long time (about 39 years), but as I recall the CDC 6400
> (at least) had no integer multiply or divide.  You had to convert to
> float first.  The other oddity about the CDC series is it's the last
> machine I've encountered that used ones-complement for ints, with two
> values for zero.
> 
> 

Well, for what it is worth… the DEC Laboratory INstrument Computer (LINC-8, sort of a forced acronym because I believe they were built to specs issued by Lincoln Labs.) and the later DEC PDP-12 (which incorporated the LINC-8 instruction set, along with the PDP-8 basic set) also did ones-complement integer arithmetic.  I never used a LINC-8, but I worked for several years around PDP-12s.  (They also had a build-in CRT and a MUX'd analog-to-digital converter with CPU instructions for driving both directly.)  As I remember, they maxed out at 32k (12-bit) words of RAM.  I don't know when they were discontinued, but there were still some PDP-12s in use as late as 1988 when I lost track. 

-Bil


> -- 
> 
> DaveA
> 
> -- 
> http://mail.python.org/mailman/listinfo/python-list