My god this issue has been around for too long. In the '80s testing folk learned to shotgun the argument space to test functions, and they've not gone an inch forward since! Or so it seems.
A version of the Pentium was released that couldn't divide by 10. And even back then, testing all the mantissas on a simulator would have taken only hours. Instead, they masked, marketed and released a tragically flawed processor.
Just test the input space exhaustively, folks! It's a computer; it feels no pain. Work it hard until it fails or works perfectly.
On most CPUs, there's plenty of 2 64-bit operands, and with SIMD instructions, plenty of CPUs have more than 1K bits total as input to the instruction. Good luck exhaustively testing those.
A version of the Pentium was released that couldn't divide by 10. And even back then, testing all the mantissas on a simulator would have taken only hours. Instead, they masked, marketed and released a tragically flawed processor.
Just test the input space exhaustively, folks! It's a computer; it feels no pain. Work it hard until it fails or works perfectly.