std.math performance (SSE vs. real)

[dennis luehring via Digitalmars-d]

Am 01.07.2014 00:18, schrieb Andrei Alexandrescu:
> On 6/30/14, 2:20 AM, Don wrote:
>> For me, a stronger argument is that you can get *higher* precision using
>> doubles, in many cases. The reason is that FMA gives you an intermediate
>> value with 128 bits of precision; it's available in SIMD but not on x87.
>>
>> So, if we want to use the highest precision supported by the hardware,
>> that does *not* mean we should always use 80 bits.
>>
>> I've experienced this in CTFE, where the calculations are currently done
>> in 80 bits, I've seen cases where the 64-bit runtime results were more
>> accurate, because of those 128 bit FMA temporaries. 80 bits are not
>> enough!!
>
> Interesting. Maybe we should follow a simple principle - define
> overloads and intrinsic operations such that real is only used if (a)
> requested explicitly (b) it brings about an actual advantage.

gcc seems to use GMP for (all) its compiletime calculations - is this 
for cross-compile unification of calculation results or just for better 
result at all - or both?