[fpc-devel] Another thread about the fact that official FPC releases are *unnecessarily* non-representative of the platforms it actually runs on

Florian Klämpfl florian at freepascal.org
Sun Sep 27 21:18:18 CEST 2020

Am 27.09.20 um 20:57 schrieb denisgolovan via fpc-devel:
>> Am 27.09.20 um 18:21 schrieb Florian Klämpfl via fpc-devel:
>> So we would need softfloat extended support. This is doable with one
>> major obstacle: the "irrational" functions like ld, sin etc.: they need
>> precise enough implementations for 80 bit (actually, just adding and
>> using in the compiler 128 bit softfloat support would be even better).
>> And this is probably something which is really hard. While I believe ;)
>> I can solve most coding challenges, this is something I fear to touch :)
> Well. Intel arch supports FMA instruction sets since 2013 (Intel) and since 2012 (AMD).
> See https://en.wikipedia.org/wiki/FMA_instruction_set

FPC supports for years (since 2014?) FMA intrinsic on CPUs having them.

> Based on FMA support it's quite easy to create 128 bits (almost) semi-soft floats.

This is a half-backen solution imo. For the compiler IEEE compliant 128 
bit floats are a must.

> Julia guys have a nice library called DoubleFloats (https://github.com/JuliaMath/DoubleFloats.jl, MIT licensed)

We cannot use MIT licensed code in the rtl.

> They have a lot of trigonometric and other "complex" stuff already implemented.
> So, maybe it's not that frightening after all :)

See above. It perfectly shows why it is frightening (not the basic 
stuff, but the transcendent functions):
- there are little libraries being really IEEE compliant for float128
- if they are IEEE compliant, their license does not allow to use the 
code in the FPC rtl.

> See my own small port attached. Russian comments ahead so beware :)
> -- Regards,
> Denis Golovan
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