To be precise, IEEE-754 floating point subtraction is functionally complete. That means you can construct any binary circuit using nothing but floating point subtraction. To see how, we must start at the bottom. I quote the IEEE 754-2019 standard, section 6.3: 6.3 The sign bit […] When neither the inputs nor result are NaN, […]; the sign of a sum, or of a difference $x−y$ regarded as a sum $x+(−y)