I thought most languages have this? If you simply write a formula operations are ordered according to the language specifiction. If you want different ordering you use parentheses.

Not sure how that interacts with this fast math thing, I don't use C

That’s a different kind of ordering.

Imagine a function like Python’s `sum(list)`. In abstract, Python should be able to add those values in any order it wants. Maybe it could spawn a thread so that one process sums the first half in the list, another sums the second half at the same time, and then you return the sum of those intermediate values. You could imagine a clever `sum()` being many times faster, especially using SIMD instructions or a GPU or something.

But alas, you can’t optimize like that with common IEEE-754 floats and expect to get the same answer out as when using the simple one-at-a-time addition. The result depends on what order you add the numbers together. Order them differently and you very well may get a different answer.

That’s the kind of ordering we’re talking about here.

The article mentioned that gcc and clang have such extensions. Having it in the language is nice though, and that's the approach Zig took.