A data processing apparatus, method and computer program product. The apparatus comprising: a register data store comprising at least three general purpose registers each operable to store a plurality of data elements; an instruction decoder operable to decode a multiplex instruction; a data processor operable to process said plurality of data elements in parallel, said data processor being controlled by said instruction decoder; and in response to said decoded multiplex instruction, said data processor being operable to specify: two of said at least three general-purpose registers as source registers, each operable to store a plurality of source data elements; a further one of said at least three registers as a control register operable to store a plurality of control values; and one of said control, or said two source registers as a destination register operable to store a plurality of resultant data elements; wherein in response to each of said plurality of control values said data processor is operable to select a corresponding data element from one of said two source registers, and to store said corresponding data element as a resultant data element in said destination register.