fn compute_ffadd_values<F: PrimeField>(
left_input: &ForeignElement<F, LIMB_BITS, 3>,
right_input: &ForeignElement<F, LIMB_BITS, 4>,
opcode: FFOps,
foreign_modulus: &ForeignElement<F, LIMB_BITS, 3>,
) -> (ForeignElement<F, LIMB_BITS, 3>, F, F, F)