Cdmtcs Research Report Series Representing Variable-length Codes in Fixed-length T-depletion Format in Encoders and Decoders Representing Variable-length Codes in Fixed-length T-depletion Format in Encoders and Decoders

T-Codes are a class of variable-length codes. Their self-synchronisation properties are useful in compression and communication applications where error recovery rather than error correction is at issue, for example, in digital telephony. T-Codes may be used without error correction or additional synchronisation mechanisms. Typically, the representation of variable-length codes is a problem in computers based on a xed-length word architecture. This presents a problem in encoder and decoder applications. The present paper introduces a xed-length format for storing and handling variable-length T-Code codewords, the T-depletion codewords, which are derived from the recursive construction of the T-Code codewords. The paper further proposes an algorithm for the conversion of T-Code codewords into T-depletion codewords that may be used as a decoder for generalized T-Codes. As well as representing all codewords of a T-Code set (the leaf nodes in the set's decoding tree), the T-depletion code format also permits the representation of \pseudo-T codewords" | strings that are not in the T-Code set. These strings are shown to correspond uniquely to all proper pre xes of T-Code codewords, thus permitting the representation of both intermediate and nal decoder states in a single format. We show that this property may be used to store arbitrary nite and pre x-free variable-length codes in a compact xed-length format.