1. Apparatus for reversing a portion of an n-bit digital word comprising: (a) bit reversing means for producing a first intermediate digital word equal to the n-bit input digital word in bit reversed order; (b) shifter means, responsive to the first intermediate digital word and to a first control input, for producing a second intermediate digital word which has a portion corresponding to the portion of the input digital word to be reversed, such portion of the second intermediate digital word equal to the portion of the input digital word in bit reversed order; and (c) selector means, responsive to the input digital word, the second intermediate digital word and a second control input, for forming an output digital word by selecting bits from either the input digital word or the second intermediate digital word.