ska_sort should reject non-IEEE 754 floating points

[Morwenn]

If I'm not mistaken, the bit tricks used to reinterpret the floating point numbers as integers are specific to the IEEE 754 representation of floating point numbers, which isn't guaranteed by the C++ standard. Instead of blindly accepting every standard floating point type, you should guard the sort at compile-time with std::numeric_limits<T>::is_iec559 so that it rejects non-IEEE 754 compliant floating points types.

Additionally, you're using type punning through an union between integral and floating point type, which is undefined behaviour. A standard compliant solution would be to use std::memcpy instead.

[Morwenn]

I added a few compile-time checks to my ska-sorter branch in cpp-sort. You might want to have some of those checks as static_assert to avoid problems such as the ones described above for float and double on strange targets :)