Update on Unums

[Nick B via Digitalmars-d-announce]

On Tuesday, 14 March 2017 at 19:32:57 UTC, H. S. Teoh wrote:
> On Tue, Mar 14, 2017 at 06:50:07PM +0000, Nick B via 
> Digitalmars-d-announce wrote:
>> On Tuesday, 14 March 2017 at 13:38:09 UTC, jmh530 wrote:
>> > On Tuesday, 14 March 2017 at 08:21:03 UTC, Andrea Fontana 
>> > wrote:
>> > > 
>> > > It seems public: 
>> > > http://insidehpc.com/2017/02/john-gustafson-presents-beyond-floating-point-next-generation-computer-arithmetic/
>> > 
>> > Also in pdf here 
>> > http://web.stanford.edu/class/ee380/Abstracts/170201-slides.pdf
>> 
>> Thank you both for posting these links :).
> [...]
>
> Indeed.
>
> But while the .pdf mentions Posits and Valids, the following 
> slides only discuss Posits.  Where's the discussion on Valids?
>
> In spite of that, though, Posits appear to be a much better 
> candidate at replacing IEEE 794 floats than the previous unum 
> incarnations. I felt the previous incarnations, while clever 
> and workable in theory, posed too many practical challenges to 
> implement on silicon.  The current description of Posits seem 
> to be much more feasible to put on silicon.
>
> Still, though, I wonder what Gustafson has up his sleeves wrt. 
> Valids.

In the Stanford presentation pdf, (note that these change from 
presentation to presentation) on page 12, is the only mention of 
Valids. I thought these were a rename of Sets of Real 
Numbers(SORNS) from his Type 2 Unums, but after reviewing the 
slides again, I'm not sure.  I believe that this needs to be 
vertified with Dr Gustafson, as you correctly point out there are 
no examples of Valids.

But when I review his slides from his New Zealand talk, there is 
an additional slide, where he states that (1) "Posit pairs beat 
intervals at their own games, too: Valid mode." and (2) "Posit 
mode: Round unum after every operation.  Valid mode: rigorous 
answer bounds; NaN answers are sets. "

If anyone wants a copy of these New Zealand slides, please advise 
me of your email address.