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Abstract

An adaptive lossless data compression system with systolic string matching logic performs compression and decompression at the maximum rate of one symbol per clock cycle. The adaptive data compression system uses an improvement of the LZ1 algorithm. A content addressable memory (CAM) is used to store the last n input symbols. The CAM is stationary, stored data is not shifted throughout the CAM, but rather the CAM is used as a circular queue controlled by a Write Address Pointer Counter (WREN). During a compression operation, a new input symbol may be written to the CAM on each clock cycle, while simultaneously the rest of the CAM is searched for the input symbol. Associated with each word of the CAM array is a String Match State Machine (SMSM) and, an address logic module (ALM). These modules detect the occurrence of strings stored in the CAM array that match the current input string and report the address of the longest matching string nearest to the Write Address Pointer. The SMSM modules constitute a systolic logic array, where state information is shifted synchronously in the direction of the Write Address Pointer. The strings are represented by a string code which includes a length value, representing the length of the string, and a position value, representing the position in the CAM of the beginning of the string. During a decompression operation, the single symbols and string codes are input to the system. The symbols are stored in the CAM and the control logic outputs the decompressed data symbols using the stored data and the string codes.

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