Apparatus for compressing data using a Lempel-Ziv-type algorithm

• US 5,903,230 A
• Filed: 07/23/1997
• Issued: 05/11/1999
• Est. Priority Date: 03/22/1995
• Status: Expired due to Fees

• Current Assignee: International Business Machines Corporation
• Original Assignee: International Business Machines Corporation
• Inventors: Masenas, Charles J.
• Primary Examiner(s): Williams, Howard L.
• Application Number:
  US08/899,205
• Time in Patent Office: 657 Days
• Field of Search: 341/51, 341/106, 341/107
• US Class Current: 341/51
• CPC Class Codes: G06T 9/005 Statistical coding, e.g. Huffman, run length coding
• CPC Class Codes: H03M 7/3086 employing a sliding window, e.g. LZ77

Abstract

A data processing system having a compression and decompression apparatus based on the Lempel-Ziv algorithm. The compression apparatus includes an array section having a circular history CAM unit for receiving and storing one or more data elements and a coding unit for determining whether received data elements previously have been stored in the history CAM unit and are a candidate for compression. If a received data element matches at least one of the stored data elements, a PS logic section determines whether there is the presence of a string. An encoding section identifies the address of the matching stored data element in a string and the length of the string. The compression apparatus generates a compression token comprising an identification of whether a data element is compressed, the length of the coded data within a plurality of predetermined data length categories and an address. The compression apparatus uses a particular hardware implementation of the PS logic section.

Claims

1. A data compression apparatus for identifying repeated data element strings in a data stream having a plurality of data elements comprising:

a history buffer for concurrently storing a plurality of the data elements in separately addressable locations, each data element being stored at an addressable location;

an input means for inputting a current data element;

a plurality of comparison means, each for comparing said current data element with the content of a stored data element then stored in a corresponding addressable location in said history buffer, said plurality of comparison means being operative to generate an output identifying all existing matches between said current data element and all stored data elements;

a plurality of logic means, each for receiving the corresponding output of one of said comparison means and for generating a signal identifying the existence of a string of at least two data elements; and

an encoder responsive to said signals from said plurality of logic means for generating a first output comprising an address identifying a repeated data element string and a second output indicating the existence of a repeated data element string within said history buffer.

2. The data compression apparatus as set forth in claim 1 wherein each of said logic means comprises a means responsive to said comparison means output and the output from another logic means for generating a match signal, a match signal from each said plurality of logic means being provided to said encoder.

3. The data compression apparatus as set forth in claim 2 wherein each said logic means further comprises a binary signal generator responsive to a match signal and said comparison means output for generating a string indicator signal.

4. The data compression apparatus as set forth in claim 3 wherein said logic means further comprises a register responsive to said binary signal generator for storing said string indicator signal for access by another logic means.

5. The data compression apparatus as set forth in claim 1 wherein said data compression apparatus is operative in accordance with a Lempel-Ziv type algorithm.

6. The data compression apparatus as set forth in claim 1 wherein said data compression apparatus is operative in accordance with an LZ1 standard algorithm.

7. The data compression apparatus as set forth in claim 1 wherein said history buffer stores current bytes in order so that successive bytes are physically adjacent in said history buffer.

8. The data compression apparatus as recited in claim 7 wherein said apparatus has a throughput of one byte per cycle, to compress a set of data.

9. The data compression apparatus as set forth in claim 1 wherein said apparatus is operational between only two states, a first for initialization and a second involving an execution of a comparison a plurality of times before ending.

10. The data compression apparatus as recited in claim 9 wherein said apparatus has a throughput of one byte per cycle, to compress a set of data.

11. The data compression apparatus as recited in claim 1 wherein said apparatus has a throughput of one byte per cycle, to compress a set of data.