1. An apparatus for selecting one of N transaction queues from which to transmit a transaction out a port of a switch in a round-robin fashion, wherein one or more of the N transaction queues may be disabled from being selected in a selection cycle, the apparatus comprising: a first input, for receiving a first value specifying which of the N transaction queues was last selected, said first value comprising N bits corresponding to said N transaction queues, wherein only one of said N bits corresponding to said last selected transaction queue is true; a second input, for receiving a second value specifying which of the N transaction queues is enabled to be selected, said second value comprising N bits corresponding to said N transaction queues, wherein each of said N bits whose corresponding transaction queue is enabled is false; a barrel incrementer, coupled to receive said first and second inputs, configured to 1-bit left-rotatively increment said second value by said first value to generate a sum; and combinational logic, coupled to said barrel incrementer, configured to generate a third value specifying which of the N transaction queues is selected next, said third value comprising a Boolean AND of said sum and an inverted version of said second value, said third value comprising N bits corresponding to said N transaction queues, wherein only one of said N bits corresponding to said next selected one of the N transaction queues is true.