1. A four-to-one multiplexer, comprising: a) a first configurable input select multiplexer comprising more than two data inputs, a first set of selection inputs, and a second set of selection inputs, wherein said first configurable input select multiplexer is configured to operate as a first two-data-input multiplexer by selection signals supplied to the first set of selection inputs from a first set of configuration storage elements, wherein the second set of selection inputs is for receiving user data to select between said two data inputs; b) a second configurable input select multiplexer comprising more than two data inputs, a third set of selection inputs, and a fourth set of selection inputs, wherein said second configurable input select multiplexer is configured to operate as a second two-data-input multiplexer by selection signals supplied to the third set of selection inputs from a second set of configuration storage elements, wherein the fourth set of selection inputs is for receiving user data to select between said two data inputs; and c) a configurable look up table, wherein said configurable look up table is configured to operate as a third two-data-input multiplexer by configuration data supplied from a third set of configuration storage elements, wherein an output of said first configurable input select multiplexer is connected to a first input of said configurable look up table, wherein an output of said second configurable input select multiplexer is connected to a second input of said configurable look up table, and wherein a third input of said configurable look up table accepts a first selection bit.