R devel - Jul 2022 - Floating point issue

> From my current experiences, I dare to say that the M1 with all
> its speed is just a tad less reliable numerically than the
> Intel/AMD floating point implementations..

80 bits floating point (FP) numbers are great, but I think we cannot rely on it
for the future.
I expect, the marketshare of ARM CPUs to grow. It's hard to predict, but ARM
may spread in desktop computers in a timeframe of 10 years, and I would not
expect it to gain extended precision FP.
Moreover, performance of FP80 is not a priority of Intel. FP80 in recent Intel
microprocessors are very slow when using special representations (NaN, NA, Inf,
-Inf) or denormal numbers.

Therefore, it may be wise to update R algorithms to make them work quite well
with 64 bits FP.

--
Sincerely
Andr? GILLIBERT

	[[alternative HTML version deleted]]

To be pedantic, the C standard does not guarantee that long double offers more
precision than double. If R?s internal FP/decimal conversion routines produce a
different result on platforms that support Intel's 80-bit precision vs.
platforms that don?t, I would classify this as a bug in R. Available precision
can affect numerical properties of algorithms but should not affect things like
decimal to binary or via versa conversion ? it either produces the accurate
enough number or it doesn?t.

As a side note, I agree with Andre that relying on Intel?s extended precision in
this day an age is not a good idea. This is a legacy feature from over forty
years ago, x86 CPUs have been using SSE instructions for floating point
computation for over a decade. The x87 instructions are slow and prevent
compiler optimisations. Overall, I believe that R would benefit from dropping
this legacy cruft. Not that there are too many places where it is used from what
I see?

Best, 

? Taras Zakharko


> On 11 Jul 2022, at 13:48, GILLIBERT, Andre <Andre.Gillibert at
chu-rouen.fr> wrote:
> 
> 
>> From my current experiences, I dare to say that the M1 with all
>> its speed is just a tad less reliable numerically than the
>> Intel/AMD floating point implementations..
> 
> 
> 80 bits floating point (FP) numbers are great, but I think we cannot rely
on it for the future.
> I expect, the marketshare of ARM CPUs to grow. It's hard to predict,
but ARM may spread in desktop computers in a timeframe of 10 years, and I would
not expect it to gain extended precision FP.
> Moreover, performance of FP80 is not a priority of Intel. FP80 in recent
Intel microprocessors are very slow when using special representations (NaN, NA,
Inf, -Inf) or denormal numbers.
> 
> Therefore, it may be wise to update R algorithms to make them work quite
well with 64 bits FP.
> 
> --
> Sincerely
> Andr? GILLIBERT
> 
> 	[[alternative HTML version deleted]]
> 
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