Re: [hatari-devel] Native FPU emulation

[Nicolas Pomarède <npomarede@xxxxxxxxxxxx>]

Le 10/10/2020 à 11:13, Thorsten Otto a écrit :
> Hi,
>
> while trying to debug an application, i just noticed that Hatari does 
> not seem to use long doubles when using native emulation 
> (USE_LONG_DOUBLE is not defined). Wouldn't it make sense to use at least 
> the long double format when available, to be closer to the m68k format, 
> even if that will not be as accurate as the softfloat emulation?
>
> Also, in uae_cpu/newcpu.h, USE_LONG_DOUBLE is defined, but to a zero 
> value. However in other places ifdef is used, which will still be true.
>
> And if i understand the code correctly, the softfloat emulation solely 
> uses the fpdata.fpx member, while the native emulation only uses 
> fpdata.fp. When switching the emulation type at runtime, i can't see any 
> attempt to convert from one field to the other (unless i missed 
> something). Instead, it seems to reset the FPU registers to all NANs. Is 
> that intended?
>
> And the file cpu/md-fpp.h does not seem to be used at all.

Hi

I might be wrong but IIRC Toni removed the long double because the extra 
cpu overhead was not worth the small accuracy gain.

For this and the other points of your message, Toni might give more 
detailed answer when he read this.

Nicolas