var product: Bus = aa.host.inputs(aa.length + bb.length)
    var multiplier: Bus = aa.host.inputs(aa.length + bb.length)
    var multiplicand: Bus = bb.host.inputs(aa.length + bb.length)

    // build shift feedbacks.
    for(i <- 1 until multiplier.length)
      multiplier(i).buildFeedback(multiplier(i-1))
    for(i <- 1 until multiplicand.length)
      multiplicand(i-1).buildFeedback(multiplicand(i))

    multiplier.buildFeedback(aa)
    multiplicand.buildFeedback(bb)

    // check whether multiplication is ready.
    // (~operands).values.reduce((A,B) => A & B)

    // final product with adder.
    product = buildAdder(product, multiplicand && multiplier(0))

    (!loadEnable, product)