[a_e_k]

C99 [0] and C++11 [1] both have fma() functions that let you directly request it without the need to mess around with sloppier FP contracts to infer it.

[0] https://en.cppreference.com/w/c/numeric/math/fma

[1] https://en.cppreference.com/w/cpp/numeric/math/fma