10. The decoder of claim 7 wherein the input words are M-bit words and the first and second output words are N-bit words, where M and N are integers and M is greater than N.
7. A decoder comprising: an input that receives input words; a mapping module that maps the input words to first output words when Hamming weights of the input words are equal to a predetermined Hamming weight and that maps the input words to second output words when the Hamming weights of the input words are not equal to the predetermined Hamming weight.