On Thursday, 3 July 2014 at 01:13:13 UTC, H. S. Teoh via
Digitalmars-d wrote:
I'm not sure I understand how removing support 80-bit floats
hurts interoperability with C? I thought none of the standard C
float types map to the x87 80-bit float?
The C spec never says anything specific about representation
because it's meant to target anything, but the x86 and AMD64 ABIs
basically say that "long double" is 80-bit for calculations. The
x86 spec says that the type is stored in 96 bits though, and the
AMD64 spec says they're stored in 128 bits for alignment purposes.
I'm still unclear whether we're aiming for C interoperability or
hardware support though, based on Walter's remark about SPARC and
PPC. There, 'long double' is represented differently but is not
backed by specialized hardware, so I'm guessing D would make
'real' 64-bits on these platforms and break compatibility with C.
So... I guess we really do need a special alias for C
compatibility, and this can map to whatever intrinsic type the
applicable compiler supports for that platform.
