Re: [Qemu-devel] [PATCH v2 02/16] softloat: disable floatx80_invalid_encoding() for m68k

[Peter Maydell]

On 30 January 2017 at 18:16, Laurent Vivier <address@hidden> wrote:
> According to the comment, this definition of invalid encoding is given
> by intel developer's manual, and doesn't work with the behavior
> of 680x0 FPU.
>
> Signed-off-by: Laurent Vivier <address@hidden>

Part of the reason these checks are here is that the code
behind them doesn't always cope nicely with the invalid
encodings.
https://lists.nongnu.org/archive/html/qemu-devel/2016-08/msg01991.html
has an x86 test case for certain sqrt inputs that cause
the floatx80_sqrt() function to go into an infinite loop,
for instance.

I guess we need to look more carefully at exactly what the
m68k does for these encodings (maybe have a 'normalize value'
function which squashes them down to whatever the equivalent
non-weird encoding is?).

thanks
-- PMM