When I'm multiplying a float using multu, should I ignore the result in the LO register?

Question

In our project, we take two floats from the user, store them in integer registers, and treat them as a IEEE 754 single precision floats, manipulating the bits by masking. So after I multiply the 23 bits of fraction value, should I take into account the result placed in the LO register if I want to return a single precision float (32 bits) as the product?

Answer 1

First off, I hope you mean 24 bits of value, since you'll need to include the implicit mantissa bit in your multiplication.

Second, if you you want your multiplication to be correctly rounded, as in IEEE-754, you will (sometimes) need the low part of the multiply in order to deliver the correct rounded result.

On the other hand, if you don't need to implement correct rounding, and you left-shift your fraction bits before multiplication, you will be able to ignore the low word of the result.