code: func (f *fieldVal) Mul(val *fieldVal) *fieldVal {
  	return f.Mul2(f, val)
  }
docs: // Mul multiplies the passed value to the existing field value and stores the
  // result in f.  Note that this function can overflow if multiplying any
  // of the individual words exceeds a max uint32.  In practice, this means the
  // magnitude of either value involved in the multiplication must be a max of
  // 8.
  //
  // The field value is returned to support chaining.  This enables syntax like:
  // f.Mul(f2).AddInt(1) so that f = (f * f2) + 1.