Variable length decoder with adaptive acceleration optimized by sub- grouping and cross-grouping the symbols having the highest probability of occurrence

摘要

A variable length decoder with adaptive acceleration in processing of an encoded input bit stream which includes an input section which receives the input bit stream and provides a decoding window that includes a sequence of bits which include one or more code words to be decoded at an output thereof. A code word length decoding section determines the combined length of a combination of two or more code words received from the input section in response to a first value of a control signal and generates a combined length signal representative of the determined combined length, and determines the length of an individual code word received from the input section in response to a second value of the control signal, and generates an individual code word length signal representative of the determined length of the individual code word. A computation loop section receives the combined length signal or the individual word length signal from the code word length decoding section and, in response thereto, shifts the decoding window to provide a new sequence of bits that include one or more additional code words to be decoded at the output of the input section. A code word value decoding section decodes the values of the combination of two or more code words provided by the input section in response to the first value of the control signal, and decodes the value of the individual code word in response to the second value of the control signal. A control section generates the control signal and controls the operation of the variable length decoder according to a decoding protocol (e.g., MPEG-2). The two or more code words of the combination of code words are part of a sub- grouped and cross-grouped set of code words of a selected group of M code words in the input bit stream whose bit lengths are ≦ than a prescribed number N. Less than all possible combinations of the selected group of M code words are stored as entries in a look-up table, so that the total number of combinations of the selected group of M code words which are stored as entries in the look-up table is less than M.sup.2.