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

[David Kastrup]

Jonas Hahnfeld <address@hidden> writes:

> Am Dienstag, den 04.02.2020, 16:57 +0100 schrieb David Kastrup:
>> Dan Eble <
>> address@hidden
>> > writes:
>> 
>> > On Feb 4, 2020, at 09:44, Masamichi Hosoda <
>> > address@hidden
>> > > wrote:
>> > > +// FIXME: workaround: In GUB, g++ 4.9.4 for darwin-x86,
>> > > +// it seems that static cast from `unsigned long long` to `double`
>> > > +// by x86 SSE2 raises an internal compile error.
>> > > +// However, static cast from `signed long long` to `double`
>> > > +// does not raise the error.
>> > > +// So we use it for a workaround.
>> > > +#if defined (__i386__) && defined (__APPLE__) && \
>> > > +  defined (__SSE2_MATH__) && __GNUC__ < 5
>> > > +    {
>> > > +      I64 inum = num_;
>> > > +      I64 iden = den_;
>> > > +      return static_cast<double> (sign_) *
>> > > +        static_cast<double> (inum) / static_cast<double> (iden);
>> > > +    }
>> > > +#else
>> > >     return (double)sign_ * (double)num_ / (double)den_;
>> > > +#endif
>> > 
>> > Is the conditional code really necessary?  Why not boil it down to the
>> > working code and a comment explaining the extra conversion to signed
>> > numbers?
>> 
>> That would be my impulse as well.  It is not like this code appears to
>> have notable drawbacks for the unafflicted platforms.
>
> Except for very funny overflows and negative signs if the value is too
> large to fit into I64 ;-P
>
> unsigned long long a = 0xC0000000;
> signed long long b = a;
> printf("%d\n", b);
> -> -1073741824

Halving the useful range before overflows is a problem, so I'll stick
with most of the guards.  Though I am skeptical that stuff exceeding I64
has much of a chance of working well, anyway.

-- 
David Kastrup