std.math performance (SSE vs. real)

[Joseph Rushton Wakeling via Digitalmars-d]

On Thursday, 3 July 2014 at 14:26:51 UTC, Iain Buclaw via 
Digitalmars-d wrote:
> It's also a handy coincidence that for many platforms the 
> targets
> largest supported FP and *double* type happen to be the same 
> too.

Out of curiosity, how is C "long double" interpreted on those 
platforms?  Just doesn't exist, or is interpreted as the same as 
double?

What's concerning me here is that you've posted at least one 
example platform where the C long double is _not_ the same as the 
largest FP type.

Now, it makes sense to me that the spec _could_ be, "real == 
largest hardware-supported FP type", and it makes sense that the 
spec could be, "real == C long double for the platform".  But it 
seems quite apparent that it can't mean both, and that there 
needs to be a firm decision about which we want it to be.