Abstract: A method and apparatus for compressing and decompressing data is described. The most frequent symbols (A-Group.) are encoded using an Arithmetic Code, then the remainder of the symbols (H-Group) are first encoded using Huffman's algorithm (or any Prefix code) and then combined with the Arithmetic code resulting in a hybrid Arithmetic/Huffman code. After being encoded into a Huffman code, the H-Group symbols are made into a "super-symbol" which fits into an Arithmetic subinterval allocated to the symbols in the H-Group. The Arithmetic subintervals for the symbols in the H-Group preferably are a negative power of 2 (e.g., 1/2, 1/4, 1/16, 1/32, etc.) of the code space. Each such H-group subinterval has its own associated subset of H-group symbols comprising one Huffman code table that fits into that respective interval. Decoding in an AMSAC system first treats the code stream as Arithmetically encoded.