case PackCategoriesIntoKey(fcZero, fcNaN):
case PackCategoriesIntoKey(fcNormal, fcNaN):
case PackCategoriesIntoKey(fcInfinity, fcNaN):
- sign = false;
+ // We need to be sure to flip the sign here for subtraction because we
+ // don't have a separate negate operation so -NaN becomes 0 - NaN here.
+ sign = rhs.sign ^ subtract;
category = fcNaN;
copySignificand(rhs);
return opOK;