std.math performance (SSE vs. real)

[Sean Kelly via Digitalmars-d]

On Wednesday, 2 July 2014 at 20:37:37 UTC, Walter Bright wrote:
> On 7/2/2014 1:53 AM, Don wrote:
>>
>> Ideally, I think we'd have a __real80 type. On x86 32 bit this 
>> would be the same as 'real', while on x86-64 __real80 would be 
>> available but probably 'real' would alias to double. But I'm a 
>> lot less certain about this.
>
> I'm afraid that would not only break most D programs, but also 
> interoperability with C.

Could you explain this?  I didn't think we used 'real' to
interface with C at all.  We might need a type to match 'long
double' in C, but what that is is already exceedingly variable.
This would probably be another case for a special alias like we
have for c_long.