[dmd-internals] longdouble and splitting off typedefs in mars.h

[Iain Buclaw]

On 18 July 2012 18:46, Rainer Schuetze <r.sagitario at gmx.de> wrote:
> On 18.07.2012 09:13, Iain Buclaw wrote:
>>
>> Hi,
>>
>> I have recently started moving across longdouble.h, and the use of
>> ldouble() over into GDC's copy of the D frontend from upstream DMD.  I
>> see there's an (attempted?) implementation for GDC already in
>> longdouble.h
>>
>>
>> https://github.com/D-Programming-Language/dmd/blob/master/src/root/longdouble.h#L16
>
>
> This was just guesswork, as I could not try it out.
>
> I wonder why the real_t implementation is necessary at all, as GCC seems to
> be capable of 80-bit floating points with "long double". At least that is
> how DMD is built on posix systems. So maybe you can also use the !_MSC_VER
> branch of the conditional.
>
>

It's there because there are a variety of representations for floating
point numbers. This means that in a cross-compiler the representation
of floating point numbers in the compiled program may be different
from that used in the machine doing the compilation.  Therefore, a
cross compiler cannot safely use the host machine's floating point
arithmetic; it must emulate the target's arithmetic. To ensure
consistency, GCC always uses emulation to work with floating point
values, even when the host and target floating point formats are
identical.


-- 
Iain Buclaw

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