what I mean here about NaNs is that from a testing perspective, I want to be able to write a test that expects NaN in the same way that I write other expectatio

what I mean here about NaNs is that from a testing perspective, I want to be able to write a test that expects NaN in the same way that I write other expectations, and you can't do that with ==. assert(x == 7); // fine assert(y == NaN); // never true assert(y != y); // this is what you meant so this equiv() helper fixes that, assert(equiv(x, 7)); // fine assert(equiv(y, NaN)); // also fine now, as far as treating NaNs equivalently, the IEEE 754 float format has a huge number of possible representations of NaN, and if you did something like a bitwise comparison, you might think that 0x7fc00000, 0x7f800001, 0xffc00000, 0x7fc0f00d were all different and not equivalent, but they're all NaNs, and I find that when I'm looking for a NaN, I very rarely care about exactly which one I'm looking at. So checking (x!=x && y!=y) admits any two NaNs as equivalent.