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unordered comparison

The fourth possible result of comparing floats - neither less, equal nor greater - which happens when either value is NaN.

IEEE 754 comparisons have four mutually exclusive outcomes, less, equal, greater and unordered; unordered holds exactly when at least one operand is a NaN, making every ordered predicate false.

Examples

  • Comparing NaN with 1.0 using ucomisd sets ZF, PF and CF all to 1: the result is unordered.

See also

floating-point compare parity flag NaN IEEE 754
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