IEEE 754’s idea was that if you got a zero in a floating-point calculation (which, at the time, meant one with physical quantities), it’s probably underflow, no

IEEE 754’s idea was that if you got a zero in a floating-point calculation (which, at the time, meant one with physical quantities), it’s probably underflow, not a legitimate result, so the FPU might as well try to give you at least a sign even if it can’t give you any significant digits. Though 754 says comparison must treat positive and negative zero as equal nevertheless, you have to deliberately choose to look at the sign (with e.g. C99’s copysign) to see the difference.