This is super useful, thanks. So if I were implementing a programming language, and wanted to have symbols to specify NaN in source code, I'd really only need quiet NaN, right? Because signaling NaN is supposed to always to raise an exception anyway?

I originally implemented Signalling and Quiet NaNs in the compiler. It was an abject failure. With all the transformations a compiler does, where the signalling turns into a quiet is lost. So just quiet NaNs are used.