musl itself expects to be configured to compile with either
-ffloat-store or -fexcess-precision=standard - but when imported
into Wine, those flags aren't used.
This seems to be essential for getting reasonable precision
from some math functions such as exp2() - without the expected
precision truncation, the output value of exp2() can be off by
as much as 0.2% in some cases.
As Wine doesn't build the musl sources with those flags, use
volatile to force storing/reloading floats in order to limit
their intermediate precision, as musl expects. Only do this on
i386 where this is known be required.
This fixes https://bugs.winehq.org/show_bug.cgi?id=56372.
Apparently this issue only appears when compiled with GCC; with
Clang, this already works as expected.
Signed-off-by: Martin Storsjö <martin(a)martin.st>
--
https://gitlab.winehq.org/wine/wine/-/merge_requests/5276
I'm not sure if it's the best way of fixing the bug. I was trying to set compilation options to workaround the problem but it didn't work well (probably due to my limited knowledge in this area).
The patch was originally sent in !5276.
--
https://gitlab.winehq.org/wine/wine/-/merge_requests/6668