Re: [hatari-devel] FPU status register handling & fmovem.x bugs

[Thorsten Otto <admin@xxxxxxxxxxx>]

On Freitag, 1. Juni 2018 13:20:15 CEST Toni Wilen wrote:
> Also, AFAIK, UAE FPU emulation (before softfloat was introduced) was
> never designed to be very accurate,

Yes, the old core use 64bit doubles only all over the place. For most real 
applications, even that is most likely not a problem, especially when the 
compiler (like GCC) also uses 64bit double by default. But on eg. Atari the 
situation is a bit different, most old applications that make use of FPU were 
compiled by Pure-C, and that uses 96bit double in this mode (even for plain 
double), so it is more likely that applications suddenly behave slightly 
different, when internally some precision is lost, or the exponent becomes too 
large to be representable in a 64bit double.

Of course, using the x87 for fpu instructions isn't really accurate either, 
but there are only some subtle differences, and it is close enough to be 
hardly noticeable. Exception handling is one thing that is maybe not quite 
right, but since the libraries in use (at least on Atari) don't provide any 
standard functions for this, this too is not a problem in practice.