Re: Misc: Applications of small floating point formats.

On Thu, 1 Aug 2024 21:55:10 +0000, EricP wrote:

MitchAlsup1 wrote:

On Wed, 31 Jul 2024 23:31:35 +0000, BGB wrote:

>
No need to elaborate on the use-cases for Binary32 and Binary64, wide
and varied.

>
There is a growing clamor for 128-bit FP, too.

>
Looking in a PDP-11 handbook from 1981, F (32-bit) and D (64-bit)
formats
there was a significant difference in operation speed for MUL and DIV.
But since the 8087 people have got used to no significant difference
(likely due to its internal use of FP80 for everything).
>
With FP128 will there again be a significant difference in speed to
FP62 or FP32 (including transcendentals)? Seems there would be because
not
every HW implementation is going to implement a full width multiplier.

One would expect FMUL and FDIV to be 4× slower in 128 than in 64, or
to consume 4 64-bit FMACs simultaneously to not be 4× slower; here
they would probably still be 1.5× slower. FADD would be 1 cycle
later.
One would expect transcendentals to be 5×-6× slower; 2× when using
4 FMAC units simultaneously.