[squeak-dev] Posits

Nicolas Cellier nicolas.cellier.aka.nice at gmail.com
Sun Nov 13 13:52:32 UTC 2022

Hi all,
the criticism of Kahan is essentially about the replacement of the variety
of rounding modes by interval arithmetic, ubox and SORN (decomposition in
union of smaller intervals to refine the bounds) as a universal solution.
It's not a criticism of the Posit format per se.
Implementing a single rounding mode certainly participates in the
simplification of the arithmetic unit, but it's not mandatory, it's
orthogonal to the representation.
Posits have a formal beauty and may reduce the complexity of hardware,
power consumption, etc...
I like the idea of using short Posits in neural networks.
It remains to see if it does not complicate error analysis, because
precision is floating (like denormals in IEEE754).
Maybe that could be a grief for Kahan too, but that would deserve an update
from his side.


Le sam. 12 nov. 2022 à 00:10, Craig Latta <craig at blackpagedigital.com> a
écrit :

> Hi Marcel--
>  > Hmm... Patrick just pointed out to me that this critique addresses
>  > Unum I. "Posits" are Unum III (Wikipedia link).
>       Sure, the Wikipedia article is where I noticed the critique. Not
> all of its criticisms are addressed by Unum II and III. And it's still
> interesting, given who wrote it. :)  I think posits are lovely, and I've
> never enjoyed dealing with IEEE 754, but it's not clear to me that the
> resource-use discussion is closed.
>  > Hmm...
>       What are you trying to say?
> -C
> --
> Craig Latta        :: research computer scientist ::
> Black Page Digital ::     Berkeley, California    ::
> 663137D7940BF5C0AF ::    C1349FB2ADA32C4D5314CE   ::
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