High-speed software implementation of Huffman coding

Summary form only given. Huffman coding has been applied in many disciplines including text compression, still image compression, and video compression. In the case of video, several software-only codecs have been developed aiming at real-time performance. However, they fall well short of achieving full screen, high-quality, and full-motion. A key bottleneck in such software implementations occurs during writing and reading of the Huffman-coded bit stream. The reason is that the minimum unit for software operations is a byte rather than a bit. Therefore, the need to read/write data in bits necessitates devising means to bridge the bits-to-bytes and and bytes-to-bits gaps efficiently. We introduce new tables for software-only Huffman coding that enable us to write/read data in M-bit units, thereby virtually eliminating the need for inefficient software simulation of bit-based operations. We present an offset-based Huffman encoding table containing information for each number of bits by which the length of a Huffman word is offset from an integral number of bytes. The number of rows in the offset-based Huffman encoding table is M times that of the general Huffman table. The offset-based Huffman encoding table eliminates most of the bit operations, but it still requires some bit-based operations to update the offset and the condition of the current unit. In order to avoid bit operations entirely, we extend the offset-based table into a byte-based table by associating a unique subtable with each offset and unit condition. A byte-based Huffman decoding table has also been studied.