An enhanced version of a recently introduced family of variable length binary codes with multiple pattern delimiters is presented and discussed. These codes are complete, universal, synchronizable, they have monotonic indexing and allow a standard search in compressed files. Comparing the compression rate on natural language texts demonstrates that introduced codes appear to be much superior to other known codes with similar properties. A fast byte-aligned decoding algorithm is constructed, which operates much faster than the one for Fibonacci codes.

Let m1, m2, . . . , mt be a fixed set of natural integers given in ascending order. A multi-delimiter code Dm1,...,mtconsists of t words of the form 1mi0 and all other binary words with suffixes having one of the forms 01mi0 that cannot occur in other places of a word, i = 1, . . . , t. Completeness, universality, and density characteristics of multi-delimiter codes are proved. Encoding of integers by multi-delimiter codes is considered in detail. For these codes, fast byte aligned decoding algorithms are also discussed. The comparison of compression rate and decoding speed of Fibonacci codes, (s, c)-dense codes and different multi-delimiter codes is presented. By many useful properties, multi-delimiter codes are superior to Fibonacci codes.

A new family of universal self-synchronizable variable-length codes is introduced. This family is not a generalization or improvement of the existing prefix codes, but is based on a new method of integer representation in a mixed base using the radix-2 and the auxiliary radix-3. Upper length bounds for such codes are obtained. The asymptotic estimates for the (2,3)-encoding including the pointwise redundancy are also given. In particular, this implies that the average length of a (2,3)-codeword is shorter than that of Fibonacci code. Elias gamma and delta codes are adopted for the (2,3) -variant with asymptotically shorter codewords as against the original case. Improvement of gamma and delta encoding for all numbers is also presented. One of (2,3)-codes with high density is highlighted as a possible candidate for practical use in data compression. The (2,3) -codes are very simple to construct and they have evident features of strong robustness.

Summary form only given. The average redundancy rate of Krichevsky's sample-based universal block codes was analyzed, in a situation wherein the samples and block codes for compression were produced from two different memoryless sources. It was proven that the average redundancy rate of adaptive block codes O/sub /spl lscr/,T/, constructed using samples of length /spl lscr/ from a source T, were used to encode block codes of length n from a source S. The adaptive block codes, constructed using samples from a source T and applied to a source S, have achieved lower average redundancy than universal codes.