[subharmonicon]

The latest standard is from 2019: https://ieeexplore.ieee.org/document/8766229

There is still some flexibility in implementation, for example how and whether FMAs are formed for a given compiler when FP_CONTRACT is ON, and in the standard itself in things like when tininess is detected.

But to your point if you stick to the basic operations in the standard, and don’t enable FP_CONTRACT and FENV_ACCESS in C/C++, have a bug free compiler and don’t use fast-math, you’re good to go.

[edit to add a caveat about compile-time constant folding which is a whole can of worms]

[edit again to point out that the C/C++ standards allow for implementations to compute intermediate results at higher precision, so a compliant implementation can use all 80 bits on x87 when computing expressions]