Some basic properties of fix-free codes

A variable-length code is a fix-free code if no codeword is a prefix or a suffix of any other codeword. This class of codes is applied to speed up the decoding process, for the decoder can decode from both sides of the compressed file simultaneously. We study some basic properties of fix-free codes. We prove a sufficient and a necessary condition for the existence of fix-free codes, and we obtain some new upper bounds on the redundancy of optimal fix-free codes.