Optimisation: we don't have to test the parity flag if we
know the test has already excluded the unordered case: eg >
and >= test for a zero carry flag, which can only occur for
By reversing comparisons we can avoid testing the parity
for < and <= as well. This works since:
- If any of the arguments is an NaN CF gets set. Resulting in a false result.
- Since this allows us to rule out NaN we can exchange the arguments and invert the direction of the arrows.