KR101857385B1 - Method and Apparatus for checking error of Lempel-Ziv 77 lossless compressed data - Google Patents

Abstract

The present invention relates to compressed data error check technique, and more particularly, to a method and an apparatus for checking whether an error occurs regardless of the number of error bits before performing decoding for data compressed by a Lempel-Ziv (LZ) 77 algorithm. The method comprises: receiving a character string to be compressed; setting a coding position; sequentially outputting an output tuple; and determining whether the compressed string is an error or not.

Description

[0001] The present invention relates to a method and an apparatus for checking error in LZ77 lossless compressed data,

The present invention relates to a compressed data error checking technique, and more particularly, to an error checking technique for checking the occurrence of an error irrespective of the number of error bits before decrypting data compressed with the LZ (Lempel-Ziv) Checking methods and devices.

The present invention also relates to an error check method and apparatus for providing information on whether or not compressed data is compressed by the LZ77 algorithm for compressed data with an arbitrary algorithm.

Data compression can be classified as loss and lossless. In a lossy compression scheme, the decompressed data may not be the same as the original data. Unlike the lossy compression method, the data type is preserved during data compression and decompression in the lossless compression method. Lossless compression schemes are classified into dictionary coding and entropy coding types.

The most widely used pre-coding algorithms are the Lempel-Ziv (LZ) algorithms made by Abraham Lempel and Jakob Ziv and their variants. In particular, the LZ77 algorithm made in 1977 confirms whether a character string to be compressed has already appeared and compresses the data by outputting a length corresponding to the position of a pointer to a character string that has already appeared, instead of outputting the character string.

However, the encoded data may cause an error in the transmission process, and the error detection method uses a parity bit. The parity bit is a method of inputting additional information in the given bit string to determine whether 1 is an odd number or an even number.

Therefore, the error is not detected when an even number of errors occur, and the parity bit itself may have an error in the data transmission process.

The most commonly used method for detecting errors is the Hamming code introduced in the 1950s by Hamming, which is called 'Hamming Code'. It has this name because it adds 3 bits of parity bits to transmit 4 bits of data.

This code has the advantage of being able to detect and correct all 1-bit errors and to detect 2-bit errors. However, the Hamming coding scheme has a limitation that an error can not be detected when an error occurs in 3 bits or more.

1. Korean Patent Laid-Open No. 2001-0084412 (entitled: Data Compression Algorithm) 2. Korean Patent Publication No. 0-2011-0007865 entitled " Data compression method "

1. Chung, Sun-Cheol et al., "Performance Improvement of LZ77 Algorithm Using Strategic Tables and Genetic Algorithms", Journal of Information Science and Technology Volume 31, Issue 12 (2004. 12) pp.1628-1636

The present invention has been proposed in order to solve the problem according to the above background art, and it is an object of the present invention to provide an error checking method capable of checking whether an error has occurred regardless of the number of error bits for data compressed with the LZ (Lempel-Ziv) The purpose of the device is to provide.

It is another object of the present invention to provide an error check method and apparatus for providing information on whether compressed data is compressed by an LZ77 algorithm with an arbitrary algorithm.

The present invention provides an error checking method capable of checking whether an error has occurred regardless of the number of error bits with respect to data compressed by the LZ (Lempel-Ziv) 77 algorithm.

The error check method includes:

(a) receiving a string to be compressed;

(b) setting a coding position at the beginning of the string to be compressed;

(c) a first portion of the lookahead buffer having a yet-to-be-compressed character string to be compressed based on the coding position in a search buffer having a character string already compressed among the characters to be compressed based on the coding position, And sequentially outputting the output tuples until the lookahead buffer is empty; And

(d) comparing the out-pooled tuples sequentially output with an error check condition set in advance, and determining the compressed string as error or no error through the LZ77 (Lempel-Ziv) algorithm according to the comparison result.

At this time, the output tuple includes a start position p according to the coding position, a string length len coinciding with the search buffer in the lookahead buffer, and a first character C not matching in the lookahead buffer . ≪ / RTI >

The step (d) includes the steps of: (d-1) confirming that the value of the start position (p) and the length (len) of the first output tuple as the first condition among the error check conditions is zero step; (d-2) checking whether the value of the start position (p) is always greater than or equal to the value of the string length (len) as a second condition of the error check condition; And (d-3) checking whether the value of the start position (p) is always smaller than or equal to a size (W) of the search buffer as a third condition of the error check condition .

The steps (d-2) to (d-3) may be repeated until the last output tuple of the LZ77 lossless compressed data is reached.

If any one of the steps (d-1) to (d-3) is not satisfied, an error is determined.

The starting position p and the string length len are expressed by L bits of L digits and the first character C is represented by 8 bits of 8 bits. .

으로 정의되는 것을 특징으로 할 수 있다.L is the size of the search buffer (W)

As shown in FIG.

In addition, the character string that can be the first character (C) may be an ASCII code.

bits(여기서, N은 아웃풋 투플의 총개수이고, M은 압축이 완료된 문자열의 길이를 나타낸다)에 의해 정해지는 것을 특징으로 할 수 있다.In addition, the compressed string is expressed by the following equation

bits (where N is the total number of output tuples and M is the length of the compressed string).

On the other hand, another embodiment of the present invention provides a data processing apparatus comprising: an input unit for inputting a character string to be compressed; A buffer unit having a search buffer having a string that has already been compressed among the input strings and a lookahead buffer having a string that has not yet been compressed; A coding position is set at the beginning of the character string to be compressed and a matching character string is found from the beginning of the lookahead buffer having an uncompleted character string in the search buffer on the basis of the coding position, An error check unit for sequentially outputting the output tuples; And an error determination unit for comparing the out-pooled tuple sequentially output with an error check condition set in advance and determining an output result string as error or no error according to a result of comparison, LZ77 (Lempel-Ziv) A check device can be provided.

 According to the present invention, it is possible to know whether or not an error has occurred before decoding the data compressed by the LZ (Lempel-Ziv) 77 algorithm.

Another advantage of the present invention is that it is possible to determine whether or not data compressed by an arbitrary algorithm is compressed by the LZ77 algorithm.

1 is a conceptual diagram showing a coding process of a general LZ (Lempel-Ziv) 77 algorithm.
2 is a configuration diagram of a compression result string output through a general LZ77 algorithm encoding process.
3 is a flowchart illustrating an error checking process of LZ77 lossless compressed data according to an embodiment of the present invention.
FIG. 4 is a block diagram of the configuration of an error checking apparatus 400 for LZ77 lossless compressed data according to an embodiment of the present invention.

While the invention is susceptible to various modifications and alternative forms, specific embodiments thereof are shown by way of example in the drawings and will herein be described in detail. It is to be understood, however, that the invention is not to be limited to the specific embodiments, but includes all modifications, equivalents, and alternatives falling within the spirit and scope of the invention.

Like reference numerals are used for similar elements in describing each drawing.

The terms first, second, etc. may be used to describe various components, but the components should not be limited by the terms. The terms are used only for the purpose of distinguishing one component from another.

For example, without departing from the scope of the present invention, the first component may be referred to as a second component, and similarly, the second component may also be referred to as a first component. The term "and / or" includes any combination of a plurality of related listed items or any of a plurality of related listed items.

Unless otherwise defined, all terms used herein, including technical or scientific terms, have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs.

Terms such as those defined in commonly used dictionaries are to be interpreted as having a meaning consistent with the contextual meaning of the related art and are to be interpreted as either ideal or overly formal in the sense of the present application Should not.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a method and an apparatus for checking error in LZ77 lossless compressed data according to an embodiment of the present invention will be described in detail with reference to the accompanying drawings.

In addition, for convenience of explanation of the invention, the following terms will be described first.

1) Input stream: the original string to be compressed

2) Output stream: Compressed compression result string

3) Character: The basic data unit of the original string to be compressed.

4) Coding position: The position of the processing point currently compressing in the input stream (matching the beginning of the lookahead buffer)

5) Lookahead buffer: string from coding position to the last character of input stream

6) Search buffer: W (= size of search buffer) characters already processed. That is, it means W strings before the coding position.

7) Pointer (p): When a matching string is found in the search buffer and lookahead buffer, it means the start position of the string and it is horizontal to several characters apart from the coding position.

8) Length (len): Length of matching string in search and lookahead buffer

9) C: the first character that does not match in the lookahead

1 is a conceptual diagram showing a coding process of a general LZ (Lempel-Ziv) 77 algorithm. Referring to FIG. 1, the compression principle of the LZ77 algorithm is to search for the longest character that coincides with the beginning of the lookahead buffer in the search buffer, And output the matching length len, (p, len) as an output stream.

Therefore, the longer the length of the found string, the higher the compression efficiency. If there is no matching character in the search buffer, the first non-matching character (C) in the lookahead buffer is stored in the search buffer. If the C character appears in the search buffer in the future, C So that it can be compressed.

The encoding of the LZ77 algorithm proceeds through the following process. (1) Position the coding position at the beginning of the input stream to be compressed. (2) Look up the longest matching string from the beginning of the lookahead buffer in the search buffer. (3) Output tuple output (p, len, C). (4) If the lookahead buffer is not empty, the coding position and the search buffer are shifted by len + 1. Repeat (2) - (4) until the lookahead buffer is empty.

As a result, the output stream output through the encoding process of the LZ77 algorithm is a form (p, len, C) in which the rows of tuples are expressed as binary codes. Where p and len are represented by binary numbers of L digits (L bits), and C is represented by 8 digits of binary codes (8 bits). At this time, L has a relationship with a size W of a search buffer and the following expression.

For example, if W is 12, L becomes 4, and p and len are represented by a 4-digit binary code. C is always represented by an 8-digit binary code, regardless of the value of W. A string that can be a C in 8 bits is equivalent to ASCII (ASCII).

bits로 구성되어 있다고 가정한다. 그리고 이해를 돕기 위해 아웃풋 투플(output tuple)에서 p에 해당하는 열(column)을

, len에 해당하는 열을

, C에 해당하는 열을

로 표현한다. 이때,

는 열의 순서를 나타내는 색인(index)으로

사이의 값을 갖는다.2 is a configuration diagram of a compression result string output through a general LZ77 algorithm encoding process. Referring to FIG. 2, for convenience of description, a compression result string (output stream)

bits. And for the sake of clarity, you can use the output tuple as a column for p

, the heat corresponding to len

, The column corresponding to C

. At this time,

Is an index indicating the order of the columns.

Lt; / RTI >

3 is a flowchart illustrating an error checking process of LZ77 lossless compressed data according to an embodiment of the present invention. In an embodiment of the present invention, it is considered that the output stream of the LZ77 algorithm has the following characteristics in order to check whether or not an error occurs in the LZ77 lossless compressed data.

In the LZ77 algorithm encoding process, the values of p and len of the first output tuple are 0 and 0, respectively. This is because p and len are 0 and 0, respectively, because there is no matching character in the search buffer and the lookahead buffer because the search buffer is empty. Then, it can be expressed by the above-mentioned variable as follows.

Therefore, it is confirmed whether _Ai = 0 and _Bi = 0 (steps S310 and S320).

If it is determined in step S320 that A _i = 0 and B _i = 0, it is detected that there is an error (i.e., error) in the output stream (step S321).

Alternatively, if in step S320, A _i = 0 and B _i = 0, increases to 1 (step S330). The value of p is always greater than or equal to the value of len. This is because the length len of the matching string in the search buffer and the lookahead buffer is equal to or smaller than p, which means the start position of the matching string. Then, it can be expressed by the above-mentioned variable as follows.

Therefore, it is checked whether A _i ? B _i (step S340).

If it is not A _{i ?} B _i in step S 340, it is detected that there is an error (i.e., error) in the output stream (step S 321).

_Otherwise , in step S340, if _Ai &_{ge; Bi} , the process proceeds to the next step.

The value of p is always less than or equal to W (= the size of the search buffer). This is because the length of the matched string can not exceed the size of the search buffer, so the value of p must be equal to or smaller than the value of W. Then, it can be expressed by the above-mentioned variable as follows.

Therefore, it is confirmed whether or not A _i? W _i (step S350).

As a result of the check, if it is not A _i? W _i in step S350, it is detected that there is an error (i.e., error) in the output result string (step S321).

Alternatively, if in step S350, A _i ≤W _i, the process proceeds to the next step.

가 마지막 열을 의미하는

값을 갖는지 확인한다. 확인 결과,

이 아니면, 에러가 있는 것으로 판정하고(단계 S321), 이와 함께 단계 S320로 진행한다. In step S390, an index indicating the order of the columns,

Means the last column

Value. As a result,

It is determined that there is an error (step S321), and the process proceeds to step S320.

이 되고, 출력 결과 문자열에 에러가 없는 것으로 판정한다(단계 S391).Finally, when the lookahead buffer is performed until the time of the borrow,

, And it is determined that there is no error in the output result string (step S391).

The conditions described above are characteristics of the output stream encoded from the LZ77 algorithm. If any one of the above three conditions is not satisfied, it can be seen that an error has occurred in the output stream.

 The error check flowchart of the LZ77 lossless compressed data shown in FIG. 3 includes a process of checking the characteristics of the above three conditions, and it is possible to check the error of the LZ77 lossless compressed data according to the above flowchart. For an output stream obtained by an arbitrary algorithm on the assumption that no error has occurred, the present invention can determine whether or not the output stream is compressed by the LZ77 algorithm.

This discrimination is further explained by the fact that the length of the compressed data differs according to the algorithm used in the compression process, even if it is the same original data. Therefore, data compressed by any compression algorithm other than LZ77 is not represented by the character string structure of FIG.

Even if the length of the output stream when the original data is compressed by an arbitrary compression algorithm coincides with the length of the output stream when compressed by the LZ77 compression algorithm and the string structure of FIG. 2 is obtained, the above three conditions are used If an error check is performed on a character string, the error detection result is obtained by at least one of the above three conditions.

That is, unlike the object of the present invention of error detection, if an output stream given in the absence of an error in the output stream data meets all three conditions for error checking of the present invention until the end of the string, the LZ77 compression algorithm As shown in FIG. On the other hand, if any one of the three conditions is not satisfied before the character string is terminated, it can be determined that the data is compressed by an arbitrary compression algorithm other than the LZ77 compression algorithm.

FIG. 4 is a block diagram of the configuration of an error checking apparatus 400 for LZ77 lossless compressed data according to an embodiment of the present invention. Referring to FIG. 4, the error check apparatus 400 includes an input unit 410 for receiving a string to be compressed, a search buffer having a string that has already been compressed and a lookup head buffer having a string yet to be compressed, A buffer unit 420 having a buffer to store a character string to be compressed, a coding position at the beginning of the character string to be compressed, and a matching character string from the beginning of the lookahead buffer having an uncompleted character string, An error determination unit 440 for comparing the out-pooled tuples sequentially output with an error check condition that is set in advance, and determining an output result string to be error or no error according to a comparison result; An encoder 450 for encoding a result string, and the like.

The already compressed string of the string to be compressed is placed in the search buffer based on the coding position, and the string of the string to be compressed, which has not yet been compressed, is placed in the lookahead buffer based on the coding position.

The term " part ", "..." and the like in Fig. 4 refer to a unit for processing at least one function or operation, which may be implemented by hardware or software or a combination of hardware and software.

(DSP), a programmable logic device (PLD), a field programmable gate array (FPGA), a processor, a controller, a microprocessor, and the like, which are designed to perform the above- , Other electronic units, or a combination thereof. In software implementation, it may be implemented as a module that performs the above-described functions. The software may be stored in a memory unit and executed by a processor. The memory unit or processor may employ various means well known to those skilled in the art.

400: Error check device
410:
420:
430: Error check section
440:
450: Encoder

Claims (9)

(a) receiving a string to be compressed;
(b) setting a coding position at the beginning of the string to be compressed;
(c) a first portion of the lookahead buffer having a yet-to-be-compressed character string to be compressed based on the coding position in a search buffer having a character string already compressed among the characters to be compressed based on the coding position, And sequentially outputting the output tuples until the lookahead buffer is empty; And
(d) comparing out-pooled tuples sequentially output with a predetermined error check condition, and determining the compressed string as error or no error through the LZ77 (Lempel-Ziv) algorithm according to the comparison result,
Wherein the output tuple includes a start position (p) according to the coding position, a character string length (len) that coincides in the search buffer and the lookahead buffer, and a first character (C) that does not match in the lookahead buffer,
The starting position p and the character string length len are represented by L bits of L digits and the first character C is represented by 8 digits of 8 bits. (Lempel-Ziv) error-checking method for lossless compressed data.
The method according to claim 1,
The step (d)
(d-1) confirming that the value of the start position (p) and the string length (len) of the first output tuple is zero (0) as a first condition of the error check condition;
(d-2) checking whether the value of the start position (p) is always greater than or equal to the value of the string length (len) as a second condition of the error check condition; And
(d-3) checking whether the value of the start position (p) is always smaller than or equal to the size (W) of the search buffer as a third condition of the error check condition How to check for errors in data.
3. The method of claim 2,
Wherein the steps (d-2) to (d-3) are repeated until the last output tuple of the LZ77 lossless compressed data is reached.
3. The method of claim 2,
And if the step of (d-1) to (d-3) is not satisfied, it is determined to be an error.
delete The method according to claim 1,
L is the size of the search buffer (W)

LZ77 < / RTI > lossless compressed data.
The method according to claim 1,
Wherein the character string that can be the first character (C) is an ASCII code (ASCII).
The method according to claim 1,
The compressed string is expressed by Equation

bits (where N is the total number of output tuples and M is the length of the compressed string).
An input unit for inputting a string to be compressed;
A buffer unit having a search buffer having a string that has already been compressed among the input strings and a lookahead buffer having a string that has not yet been compressed;
A coding position is set at the beginning of the character string to be compressed and a matching character string is found from the beginning of the lookahead buffer having an uncompleted character string in the search buffer on the basis of the coding position, An error check unit for sequentially outputting the output tuples; And
And an error determination unit for comparing the out-pooled tuple sequentially output with an error check condition set in advance and determining the compressed string as an error or no error through the LZ77 (Lempel-Ziv) algorithm according to the comparison result,
Wherein the output tuple includes a start position (p) according to the coding position, a character string length (len) that coincides in the search buffer and the lookahead buffer, and a first character (C) that does not match in the lookahead buffer,
The starting position p and the character string length len are represented by L bits of L digits and the first character C is represented by 8 digits of 8 bits. LZ77 (Lempel-Ziv) error checking device for lossless compression data.

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