Fujitsu Corporation

Fijitsu Limited

Noriko Satoh

Shigeru Yoshida

Yoshiyuki Okada

Takashi Morihara

Hironori Yahagi

A symbol string detection unit detects the second symbol string matching the first symbol string having a predetermined length n from input character strings. A matching length detection unit detects a matching length k between the third symbol string following the first symbol string and the fourth symbol string following the second symbol string. A coding unit codes an input symbol string based on the symbol string detected by the symbol string detection unit and the matching length k detected by the matching length detection unit.

Encoding and decoding apparatus with matching length means for symbol strings

The present invention provides a data compression method in which a plurality of consecutive characters of a data string to be compressed are set as a character string to be searched for. Bits of a bit string representing the set character string are allocated to at least two codewords. Thus, first and second searching codewords are generated. These first and second codewords are used as array addresses. First and second array tables are prepared, in which information on the past occurrence positions of the set character string is previously entered as the contents thereof. When the first and second codewords are generated from the character string to be compressed, the first and second array tables are looked up by using these codewords as the addresses of the arrays. When results of looking up these tables match with each other, it is found that the set character string occurred in the past. Thus, information on the past occurrence position information of the set character string is obtained according to the obtained array content. Then, this information is encoded, so that data compression is performed. Thus, the amount of memory needed for the tables is significantly reduced, while information on the past occurrence position of the set character string is obtained without reducing a searching speed.

Method and apparatus for compressing data string

A tag information separating unit separates a tag identified from a character train stream and outputs as tag information. A tag code replacing unit arranges a tag code for identification to a position of the character train stream in which the tag was separated. A character train coding unit compression encodes the character train stream including a tag code which is outputted from the tag code replacing unit. A data reconstructing apparatus reconstructs the character train stream by the operation opposite to the compression.

Data compressing apparatus, reconstructing apparatus, and method for separating tag information from a character train stream of a structured document and performing a coding and reconstruction

Words and word codes corresponding to the words are registered in advance. If an unregistered word appears when data are compressed, the code of the leading character of the word is divided into a plurality of parts in a specific size, a predetermined additional code is added to generate a code of the same length as the word code. Thus, the compressed data can be treated as fixed length codes. When the compressed data are decompressed, the code of an unregistered character is identified using this additional code.

Data compression/decompression apparatus using additional code and method thereof

Encoding and decoding apparatus using context

The present invention provides a data compression method in which a plurality of consecutive characters of a data string to be compressed are set as a character string to be searched for. Bits of a bit string representing the set character string are allocated to at least two codewords. Thus, first and second searching codewords are generated. These first and second codewords are used as array addresses. Fist and second array tables are prepared, in which information on the past occurrence positions of the set character string is previously entered as the contents thereof. When the first and second codewords are generated from the character string to be compressed, the first and second array tables are looked up by using these codewords as the addresses of the arrays. When results of looking up these tables match with each other, it is found that the set character string occurred in the past. Thus, information on the past occurrence position information of the set character string is obtained according to the obtained array content. Then, this information is encoded, so that data compression is performed. Thus, the amount of memory needed for the tables is significantly reduced, while information on the past occurrence position of the set character string is obtained without reducing a searching speed.

Provided is a probabilistic statistical data compression/restoration method for variable-length encoding a source character and restoring a variable-length code to a character using the probability of occurrence of the source character which appears following a character string (context) of n characters which immediately precede the source character. When variable-length encoding is performed, a context registration unit successively registers context based upon an entered character without fixing the length (degree) of context, and a compressing encoder selects registered context satisfying a predetermined condition, e.g., registered context for which the frequency of occurrence is greater than a fixed value, as context (encoding context) used in encoding, and variable-length encodes a source character by using this encoding context. A restoration unit restores a code to a character by executing processing which is the reverse of the processing executed by the compressing encoder.

Statistical data compression/decompression method

A data compressing technique and a data decompressing technique provide a compressing dictionary storing unit for storing a compressing dictionary usable when data to be compressed is compressed, a compressing dictionary use or non-use deciding unit for deciding whether the compressing dictionary is to be used or not when the data to be compressed is compressed, and a coding unit for coding the data to be compressed on the basis of the compressing dictionary when the compressing dictionary use or non-use deciding unit decides the compressing dictionary is to be used, whereas not coding but outputting the data to be compressed when the compressing dictionary use or non-use deciding unit decides the compressing dictionary is not to be used, thereby stably achieving a preferable compression ratio for a small quantity of data such as text data in a text file.

DATA COMPRESSING APPARATUS AND A DATA DECOMPRESSING APPARATUS, A DATA COMPRESSING METHOD AND A DATA DECOMPRESSING METHOD, AND A DATA COMPRESSING OR DECOMPRESSING DICTIONARY CREATING APPARATUS AND A COMPUTER READABLE RECORDING MEDIUM STORING A DATA COMPRESSING PROGRAM OR A DATA DECOMPRESSING PROGRAM

A character string of which a start point is each address of character string data in an input buffer is rearranged in the predetermined order, so that a rank list is generated. Next, the location of the matching candidate of a character string to be encoded is obtained on the basis of the rank list. Then, the character string to be encoded is compared with a matching candidate, thereby obtaining a matching length. Further, a code is generated using the location of the matching candidate and the matching length, and the code is output as compression data.

Apparatus for repeatedly compressing a data string and a method thereof

Encoding and decoding apparatus with matching length detection means for symbol strings

A data compression apparatus is capable of compressing data at a high compression rate and at a high speed. A data decompression apparatus is used in combination with this data compression apparatus to decode the compressed data. The data compression apparatus includes a RAM which stores Huffman code trees each of which corresponds to a character string, i.e. 'context.' A CPU encodes each character which is to be encoded by use of a Huffman code tree corresponding to the context at that time. Each time a character is encoded, the Huffman code tree used is reconstructed so as to account for the encoded character. The data decompression apparatus stores Huffman code trees corresponding to contexts respectively, decodes the code to be decoded by use of a Huffman code tree corresponding to the context (a character string previously decoded). Each time one character is decoded, the Huffman code tree used for decoding is reconstructed so as to account for the decoded character.

Method of and apparatus for compressing and restoring data

A data compressing method involves the use of a data string registering unit for registering a charactor or charactor string and the context and a code information registering unit for registering coding information of the character or character string following the context, the coding information following previous a input data. The data compressing method includes a data string new registering step of, when the input character or character string and the context set is not registering in the string registering unit, register the set in the data string registering unit. The same method also includes a code information new registering step of, when the input character or character string's code information following the context is not registering in the code information registering unit, register the code information in the code information registering unit and a code outputting step of outputting the code following the code information registered in the code information registering unit and a code information updating step of updating the code information registering unit.

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Kawasaki, Japan

Noriko Satoh