Re: [Qemu-devel] [PATCH v5 3/6] target-m68k: use floatx80 internally

[Richard Henderson]

On 06/21/2017 09:18 AM, Philippe Mathieu-Daudé wrote:
> > +typedef CPU_LDoubleU FPReg;
>
> What an awful name... Anyway checking on "qemu/bswap.h" it seems there is some 
> endianess issue with it if your host is little-endian.

There is no endian-ness issue because we do not attempt to read that structure 
from memory as a whole.  Instead, Laurent uses two big-endian loads (with 
appropriate address arithmetic) and stores the result into this host structure 
in host-endian order.  Further, the host routines use the structure members by 
name and do not assume any particular relationship between them.

> Do you have a way to run Berkeley TestFloat?

As noted in Laurent's cover message, floatx80 isn't quite right -- that is the 
x86 data type, and the proper m68k data type is slightly different.

I would expect the results from using floatx80 to be Just Good Enough to 
produce a working m68k user-land.  It will produce correct results for normal 
numbers in arithmetic such as 1.0 + 10.0.  But I would expect many of the edge 
conditions that TestFloat would attempt (especially de-normals and un-normals) 
would fail.


r~