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Why do you return x-x for inf or nan? I can't test now, but I imagine they both return nan?

I run a high performance math library in C#, and I'm always looking to improve.

It's an easy way to return nan and set FE_INVALID. If you're not worried about floating point exceptions you can just return NaN directly. Idk how much C# even guarantees about the floating point operations and if it's applicable there.

https://en.cppreference.com/w/cpp/numeric/fenv/FE_exceptions

Using the expression ensures that the FP exceptions are properly set. It also does quieting of sNaN or NaN payload propagation as appropriate.

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