Byte swap instruction for memory format conversion within a microprocessor

A microprocessor instruction for performing an in-place byte swap on 32-bit data type to convert data stored in a big-endian memory format to a little-endian memory format, or visa-versa, is described. The invention comprises a modified barrel shifter which includes a plurality of multiplexers for selectively coupling data from one or more input buses to an output bus. The coupling of the individual bit lines of the data buses is arranged such that the lower order bits of the 32-bit quantity are exchanged with the higher order bits and visa-versa. Control lines connected to each of the multiplexers provide a means for controlling the byte swapping operation.