Re: Inline assembler fallback for _FPU_SETCW() missing in MINGW libraries (issue 577450043 by address@hidden)

[Masamichi Hosoda]

>> This sounds promising.
>>
>>>           -fexcess-precision=standard is not implemented for languages
>>>           other than C.
>>
>> Never mind.
> 
> Hm.  Maybe
> 
> -mfpmath=sse
> 
> instead?  The problem with switching the whole FPU to reduced precision
> is that some library functions might not expect that, so it is making me
> queasy.  On the other hand, using SSE might have a negative performance?
> I just don't have a good idea what we are dealing with here.

In my experiment, `-fexcess-precision=standard` cannot be used for C++.

```
$ g++ -fexcess-precision=standard test.cc
cc1plus: sorry, unimplemented: -fexcess-precision=standard for C++

$ g++ --version
g++ (GCC) 7.4.0
Copyright (C) 2017 Free Software Foundation, Inc.
This is free software; see the source for copying conditions.  There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.


$
```

On the other hand, `-msse -mfpmath=sse` uses SSE,
which can only perform single-precision floating-point calculation.
SSE is too low precision.

`-msse2 -mfpmath=sse` uses SSE2,
which can perform double-precision floating-point calculation.
Precision is sufficient, but older 32-bit x86 CPUs do not have SSE2.