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

[Philippe Mathieu-Daudé]

On Wed, Jun 21, 2017 at 1:37 PM, Richard Henderson <address@hidden> wrote:
> On 06/21/2017 09:18 AM, Philippe Mathieu-Daudé wrote:
>> 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.

Ok, thank your Richard for this clear explanation.
("Endian-ness" ok, Peter also corrected me, I'll give a try to some speller...)

>
>> 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.

Ok. I'm asking thinking about cross unit-tests I can add to our
continuous integration system, this might be a candidate.

Regards,

Phil.