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Re: Exact integer-valued floats

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  Re: Exact integer-valued floats Tim Roberts <timr@probo.com> - 2012-09-22 22:27 -0700

#29791 — Re: Exact integer-valued floats

True.  Seymour wanted all of the integer instructions to be combinatorial logic, rather than iterative.  Fortunately, since the floating point binary point was to the right, it was trivial to pack integers to float, do a floating computation, then unpack back to integer.

Apologize in advance for top-posting.  My Xoom makes bottom-posting awkward.
--
Tim Roberts, timr@probo.com
Providenza & Boekelheide, Inc.

Dave Angel <d@davea.name> wrote:


On 09/22/2012 05:05 PM, Tim Roberts wrote:
> Dennis Lee Bieber <wlfraed@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.


--

DaveA

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