Support MulAdd and MulAddAssign for no_std

[Schultzer]

Is MulAdd and MulAddAssign supported for no_std?

I looked at the docs for for f64 and as far as I understand there shouldn't be any problem in making these traits no_std.

Looking at the code for mul_add it looks like only std is supported?

https://doc.rust-lang.org/core/intrinsics/fn.fmaf32.html
https://doc.rust-lang.org/core/intrinsics/fn.fmaf64.html

[cuviper]

The core impl f64 does not include mul_add, nor anything else based on intrinsics. We can't call the intrinsics directly because they are marked unstable, for use only with nightly versions of rustc. So while the MulAdd traits do exist under no_std, we don't have a way to implement them for floats.

I think core doesn't use intrinsics because LLVM may lower them to external calls on some targets.

[Schultzer]

I guess this can only be done with libm with the F32Ext and F64Ext

[cuviper]

Oh, #99 actually does include this!

[cuviper]

The libm feature is now supported in 2.0.9.