1. A method for testing bit field contents contained in a source, the source comprising a full complement of source bits, the bit field comprising less than the full complement of source bits and having a size and position within the source, the method comprising: encoding the position and the size of the bit field into a reference field; creating a mask using the position and size in the reference field; performing a combined function, the combined function comprising shifting the position of the bit field to form a shifted result and employing the mask to select between the shifted result within the range of the bit field and uniform predetermined values, said employing forming a full width intermediate value, wherein bit positions outside the bit field are set to the uniform predetermined values; and combining all bits in the full width intermediate result to form a final result.