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)
    var adder: Bus = buildAdder(product, multiplier && multiplicand(0))
    product.buildFeedback(adder)

    var anyTrueGate: Gate = new ConstantGate(multiplicand.host, false)
    for (i <- 0 until multiplicand.length)
      anyTrueGate = anyTrueGate || multiplicand(i)
    var anyTrueGate2: Gate = new ConstantGate(multiplier.host, false)
    for (i <- 0 until multiplier.length)
      anyTrueGate2 = anyTrueGate2 || multiplier(i)
    var readyGate: Gate = !loadEnable && (!anyTrueGate || !anyTrueGate2)

    // build shift feedbacks.
    var zero: Bus = aa.host.falses(1);
    multiplier(0).buildFeedback(aa(0) && loadEnable)
    for(i <- 1 until multiplier.length-1) {
      if(i < aa.length) {
        multiplier(i).buildFeedback((multiplier(i-1) && !loadEnable) || (aa(i) && loadEnable))
      } else {
        multiplier(i).buildFeedback(multiplier(i-1) && !loadEnable)
      }
    }
    for(i <- 1 until multiplicand.length) {
      if(i <= bb.length) {
        multiplicand(i-1).buildFeedback((multiplicand(i) && !loadEnable) || (bb(i-1) && loadEnable))
      } else {
        multiplicand(i-1).buildFeedback(multiplicand(i) && !loadEnable)
      }
    }

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

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

    (readyGate, product)