Apparatus for variable-length decoding image signals using a run

Abstract

An apparatus for decoding variable-length codewords has a FIFO memory which stores a bitstream and outputs an N-bit sequence from the first bit position in the stored bitstream in response to a carry signal. The number of bits 'N' corresponds to the longest variable-length codeword. A barrel shifter receives part of a 2N-bit sequence in response to the carry signal, and outputs an N-bit sequence in response to the accumulated codeword length. Another barrel shifter outputs an N-bit sequence in response to the codeword length for storing the 2N-bit sequence from the first barrel shifter. The decoder generates a run-length and a level corresponding to a variable-length codeword starting at a first bit position in the N-bit sequence. The decoder generates a second run equivalent signal during a run-length interval, and then outputs data of '0' in response to the second run equivalent signal, and outputs a level in response to the first run equivalent signal. A codeword length generator generates a codeword corresponding to the first variable-length codeword in the output of the second barrel shifter. An operator adds and modulo-N-operates a previously accumulated codeword length and a codeword length from the codeword length generator and outputs the residue as an accumulated codeword length and the quotient as a carry signal.