Meltzer, Lippe, Goldstein, et al.
Variable length coding system having a zig-zag FIFO for selectively storing each data coefficient and zero-run count
 A variable length coder is disclosed having a zig-zag FIFO that is supplied with coefficient blocks prior to encoding. The zig-zag FIFO has a comparator for comparing each coefficient of each coefficient block with zero. The zig-zag FIFO also has a counter responsive to the comparator. The counter increments a count therein by one for each received zero AC coefficient of each run, i.e., each continuous sequence, of zero AC coefficients contained in each block. The zig-zag FIFO also has a FIFO circuit which is responsive to both the comparator and counter. The FIFO stores each DC coefficient and each non-zero AC coefficient of each zig-zag scanned block in the order in which they are received. The FIFO also stores the count of the counter (i.e., the zero run length) for each run of zero AC coefficients in the order in which the run appears in the zig-zag scanned block of coefficients. 
Industrial Technology Research Institute
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Yueh-Chang
Chen