Abstract: A method and apparatus are provided for performing a fast sum-and-compare operation. The apparatus of the present invention utilizes a single carry save adder in conjunction with a zero detect circuit for performing logic operations to determine whether or not the sum of a plurality of operands is equal to one or more constants. The Carry Save Adder generates a sum, M, and carry, L, that are output from the carry save adder to the zero detect circuit. The zero detect circuit produces internal carry signals that are passed between adjacent bit-cells of the zero detect circuit. The zero detect circuit generates outputs Zk1 through Zkn which are true if the condition A+B+C={k1, k2, k3 . . . kn} for all constants k1 through kn. The carry signals propagate through only one bit of the zero detect circuit, thereby providing the sum-and-compare circuit of the present invention with extremely high speed.

Abstract: A sum-and-compare circuit is provided which minimizes propagation delay and which minimizes the amount of die area required to implement the sum-and-compare circuit. The sum-and-compare circuit comprises a propagate/generate logic block followed by a carry-lookahead tree structure. The propagate/generate logic block receives a first operand, A, a second operand, B, and a third operand, J. The first operand A corresponds to an addend, the second operand B corresponds to an augend, and the third operand J corresponds to the twos compliment of the constant K. The propagate/generate logic block comprises logic configured to add the operand A to the operand B to obtain a first sum and logic configured to add the first sum to the operand J to obtain a plurality of propagate signals and a plurality of generate signals, which are then output from the propagate/generate logic block to a carry-lookahead tree structure.

Abstract: A single clock cycle adaptive data compressor/decompressor with a string reversal mechanism is described which can perform data compression and decompression at the rate of one uncompressed symbol per clock cycle. The LZW data compression algorithm has been improved for use in this data compressor. The compressor builds a string table as the data is received. Each string within the table is made up of the address within the table of the longest previously seen matching string and the one character that makes this string different. This data compressor/decompressor utilizes a content addressable memory to store the string table. This content addressable memory allows the compressor to store the current symbol string in a table while that same string table is simultaneously searched for the current string. During decompression the characters within a symbol string are output in reverse of the order in which they were input.

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.

Abstract: A content addressable memory cell includes six transistors connected together to perform memory read, memory write, and matching operations. This cell has the ability to perform typical memory write and memory read operations as well as the capability of signalling whether or not its stored data matches data that is being searched for. A cross-coupling scheme is used in the memory cell so that a high potential will always be stored on the gate of a transistor whose source is at ground. This cross-coupling scheme increases the amount of charge stored on the storage transistor and decreases the required frequency of refresh operations. In addition to the transistors configured to store data, an additional transistor configured as a diode is used as a rapid discharge path to maximize the efficiency of the cell during a read operation. During a match operation another transistor is utilized to discharge the Match line quickly in the event the stored data does not match the data that is being searched for.

Abstract: A content addressable memory cell includes six transistors connected together to perform memory read, memory write, and matching operations. This cell has the ability to perform typical memory write and memory read operations as well as the capability of signalling whether or not its stored data matches data that is being searched for. A cross-coupling scheme is used in the memory cell so that a high potential will always be stored on the gate of a transistor whose source is at ground. This cross-coupling scheme increases the amount of charge stored on the storage transistor and decreases the required frequency of refresh operations. In addition to the transistors configured to store data, an additional transistor configured as a diode is used as a rapid discharge path to maximize the efficiency of the cell during a read operation. During a match operation another transistor is utilized to discharge the Match line quickly in the event the stored data does not match the data that is being searched for.