[Libre-soc-bugs] [Bug 541] implement nmigen HDL IEEE754 and Khronos FP transcendentals needed for 3D (CORDIC ones)

[bugzilla-daemon at libre-soc.org]

https://bugs.libre-soc.org/show_bug.cgi?id=541

--- Comment #6 from Jacob Lifshay <programmerjake at gmail.com> ---
(In reply to Luke Kenneth Casson Leighton from comment #5)
> (In reply to Jacob Lifshay from comment #4)
> 
> > meaning it takes extra silicon to implement the low-accuracy variant that we
> > can't use anyway
> 
> the cost of the gates is irrelevant [except for leakage current],
> it doesn't come into the equation of satisfying both end-user
> requirements.
> 
> that post clearly indicates that there are different user requirements,
> where different hardware fails to meet both.
> 
> i will state it again: we may solve this by providing the *end users*
> the option to choose the level of accuracy that they require.
> 
> what the Khronos Group demands can take a back seat.

Sounds good to me as long as we have a decently performant implementation with
higher accuracy that is good enough to use by default.

The Vulkan spec's accuracy requirements are honestly on the level I'd expect
for machine learning or f16, not f32. I think we should have the accuracy
requirements we expect for a GPU-class implementation be closer to <= 4 ULP
(iirc the OpenCL spec).

For CPU stuff, I'd expect <= 1 ULP (since absolutely correct outputs are sooo
hard to get right)

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