[vsipl++] patch: sal/fft.hpp fix

[Stefan Seefeld]

Jules Bergmann wrote:
> Stefan Seefeld wrote:
>> The attached patch removes the incorrect use of SFINAE by a more
>> explicit form to indicate that the SAL backend doesn't support
>> long double types. Before this patch the SAL backend was always
>> skipped. Ok to check in ?
> 
> Stefan,
> 
> How would the SAL FFT react if a user accidentally tried to do an FFT on 
> integral data?
> 
> Instead of listing the types that SAL doesn't support (long double), 
> could you instead list the types that it does support?

That's what I tried with my sfinae approach. I agree that having an inclusive
list is better than an exclusive (incomplete) list, and I'm still thinking about
how to do that, without having to duplicate all the evaluator logic for all
supported types.

Meanwhile, I'd like to specifically disable long double for sal since fftw
supports it, and thus it makes sense to have tests trying to run FFTs
with long double types.

Regards,
		Stefan