use SLEEF trigonometric math

[Andarwinux]

SLEEF can be used not only for FFT, but also for trigonometric functions, which is very useful for platforms such as MinGW where libm has very poor performance.

[cannam]

Interesting - the last time SLEEF was mentioned here (#90) it was to question whether we were wise to support it at all. But it looks to be more actively maintained now, which is nice.

I vaguely recall some practical difficulty matching the Sleef trigonometric function APIs to what we need, but I don't remember very clearly and things may have changed more recently anyway. I agree it sounds like a potentially good idea, I'll have to take another look.

[Andarwinux]

Interesting - the last time SLEEF was mentioned here (#90) it was to question whether we were wise to support it at all. But it looks to be more actively maintained now, which is nice.

#90 is just a result of vcpkg itself using the wrong way to package SLEEF, and development on master remains active. I don't think there's anything wrong with SLEEF itself, and it's recently gotten some funding from Arm.

I vaguely recall some practical difficulty matching the Sleef trigonometric function APIs to what we need, but I don't remember very clearly and things may have changed more recently anyway. I agree it sounds like a potentially good idea, I'll have to take another look.

Thanks! MinGW's math functions are implemented using x87 inline asm, so this is a huge performance bottleneck, and clang/gcc's -fveclib doesn't support MinGW either, so I can only look for a more direct way.