KR101890365B1 - Method and apparatus for error detection in compressed data - Google Patents

Abstract

A method for detecting whether an error is included in compressed data comprises the steps of: checking a value of a flag bit included in the compressed data; performing a first inspection on eight bits after the flag bit in the compressed data when the value of the flag bit is one; and performing a second inspection on 2*L number of bits after the flag bit in the compressed data when the value of the flag bit is zero.

Description

[0001] The present invention relates to a method and apparatus for detecting errors in compressed data,

And to a method and apparatus for detecting whether or not an error is contained in compressed data.

Data compression technology refers to a technique for reducing the capacity of data so that data can be efficiently recorded in a limited storage space. Such data compression techniques are largely divided into lossy compression techniques and lossless compression techniques. In the case of the lossy compression technique, since loss of original data occurs in the process of compressing the original data, it is impossible to restore the compressed data to original data. On the other hand, in the case of lossless compression technology, it is possible to restore compressed data to original data because information loss of original data does not occur during compression of original data.

Lossless compression techniques can be classified into entropy encoding and dictionary encoding techniques. The entropy encoding technique expresses the symbols that appear most frequently in the original data with the shortest code and expresses the symbols with the smallest occurrence frequency with the longest code. That is, the original data is compressed by varying the length of the code representing the symbol according to the frequency of occurrence of the symbol. The dictionary-based compression technique checks whether there is a matching character string between the current compressed character string and the previously compressed character string in the original data, and if there is a matching character string, the length information of the matching character string is used And compress the original data.

There are algorithms derived from the LZ77 (Lempel-Ziv77) algorithm and the LZ77 algorithm by Abraham Lempel and Jakob Ziv in 1977, which are the most widely used pre-coding techniques to date. In particular, the LZSS algorithm is one of the derived algorithms of the LZ77 algorithm, and was created by James Storer and Thomas Szymanski in 1982. In the existing LZ77 algorithm, if there is at least one matching character between a string to be compressed and a compressed character string, the LZ77 algorithm compresses the length of the character string corresponding to the position value of the character. In general, one character is represented by 8 bits, while the position value and length information are represented by more than 8 bits. Therefore, in the LZ77 algorithm, there is a problem that the compressed data becomes larger than the original data. To solve this problem, the LZSS algorithm does not compress the characters if the number of matching characters does not exceed a certain number. If the number of matching characters is equal to or greater than a certain number, the characters are compressed using the number information of the character string that coincides with the position information of the matching character string, as in the compression method of the LZ77 algorithm. In the LZSS algorithm, a 1-bit flag is inserted between the character strings to distinguish whether the compressed data is data indicating a character string or data indicating the number of character strings matching position information of a matching character string.

Currently, the most widely used error detection method is Hamming's method developed in the 1950's, which inserts additional bits called a Hamming code into a compressed data bit stream and analyzes the relationship between the bits Detection is performed. However, when an error is detected using a Hamming code, there is a disadvantage that the code rate is lowered. For example, in the case of the Hamming (7,4) code, since the 3-bit Hamming code is added to perform error detection on the 4-bit data, it is named Hamming (7,4) , 4) The code rate of the code is 4/7? 0.57. Therefore, it is indispensable for error detection to record the compressed data in which the Hamming code is inserted to the storage medium, but it is difficult to say that it is an efficient method when considering the limited storage space of the storage medium.

And a method and an apparatus for detecting whether or not an error is contained in compressed data. The present invention also provides a computer-readable recording medium on which a program for causing the computer to execute the method is provided. The technical problem to be solved is not limited to the technical problems as described above, and other technical problems may exist.

A method of detecting whether or not an error is included in compressed data according to one aspect includes: checking a value of a flag bit included in the compressed data; Performing a first check on the eight bits after the flag bit in the compressed data if the value of the flag bit is one; And performing a second check on 2 * L bits after the flag bit in the compressed data when the value of the flag bit is 0, wherein L is a natural number of 1 or more, And is determined by the size of a search buffer.

In the above-described method, the second check may include determining whether a value indicated by the preceding L bits of the 2 * L bits is greater than or equal to a value indicated by the following L bits; Checking whether the value indicated by the preceding L bits is less than or equal to a value corresponding to the size of the search buffer; And verifying that the value represented by the L bits following is less than or equal to a value corresponding to the size of the lookahead buffer.

In the above method, the first check includes checking using a parity bit.

In the above-described method, the 2 * L bits include information on a position in the search buffer of a character string representing a predetermined pattern in data before the compression is performed, and information on the length of the character string .

In the above-described method, the compressed data includes compressed data based on the LZSS algorithm.

The method may further include receiving the compressed data.

A computer-readable recording medium according to another aspect includes a recording medium on which a program for causing a computer to execute the above-described method is recorded.

An apparatus for detecting whether or not an error is included in compressed data according to another aspect includes: a communication interface unit for receiving the compressed data; And checking a value of a flag bit included in the compressed data if a value of the flag bit is 1, and performing a first check on 8 bits after the flag bit in the compressed data And performing a second check on 2 * L bits after the flag bit in the compressed data if the value of the flag bit is 0, wherein L is a natural number greater than or equal to 1 , And the size of the search buffer.

In the above-described apparatus, the processor checks if the value indicated by the preceding L bits of the 2 * L bits is greater than or equal to the value represented by the following L bits, and if the preceding L bits indicate Value is less than or equal to a value corresponding to the size of the search buffer and whether the value indicated by the L bits after the L is less than or equal to a value corresponding to the size of the lookahead buffer.

In the above-described apparatus, the first check includes a check using a parity bit.

In the above-described apparatus, the 2 * L bits include information on a position in the search buffer of a character string representing a predetermined pattern in data before the compression is performed, and information on the length of the character string .

In the above-described apparatus, the compressed data includes compressed data based on the LZSS algorithm.

According to the present invention, error detection can be performed on data compressed with the LZSS algorithm without additional bit insertion. Further, according to the present invention, it is possible to determine whether or not the compressed data is compressed by the LZSS algorithm on the assumption that no error has occurred.

1 is a block diagram for explaining an example of an error detecting apparatus according to an embodiment.
2 is a diagram for explaining an example in which data according to an embodiment is compressed based on the LZSS algorithm.
FIG. 3 is a flowchart illustrating an example of a method for detecting whether or not an error is included in compressed data according to an exemplary embodiment.
4 is a view for explaining an example of compressed data according to an embodiment.
5 is a flow diagram illustrating an example of the operation of a processor in accordance with one embodiment.

Although the terms used in the embodiments have been selected in consideration of the functions in the present invention, it is possible to select general terms that are widely used at present. However, these may vary depending on the intention of the person skilled in the art or the precedent, the emergence of new technology. Also, in certain cases, there may be a term selected arbitrarily by the applicant, in which case the meaning thereof will be described in detail in the description of the corresponding invention. Therefore, the term used in the present invention should be defined based on the meaning of the term, not on the name of a simple term, but on the entire contents of the present invention.

When an element is referred to as " including " an element throughout the specification, it is to be understood that the element may include other elements as well, without departing from the spirit or scope of the present invention. In addition, the term " "... Module " or the like means a unit for processing at least one function or operation, which may be implemented in hardware or software, or a combination of hardware and software.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings so that those skilled in the art can easily carry out the present invention. The present invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

1 is a block diagram for explaining an example of an error detecting apparatus according to an embodiment.

Referring to FIG. 1, the error detection apparatus 100 includes a processor 110, a communication interface unit 120, and a memory 130. The processor 110 includes an identification unit 111, a first checking unit 112, and a second checking unit 113.

Only the components related to the present embodiment are shown in the error detecting apparatus 100 shown in FIG. Therefore, it will be understood by those skilled in the art that other general components other than the components shown in FIG. 1 may be further included in the error detecting apparatus 100.

It should be noted that the processor 110, the communication interface 120 and the memory 130 of the error detecting apparatus 100 shown in FIG. 1 may exist as independent apparatuses, If you have someone, you can know.

The processor 110 may be implemented as an array of a plurality of logic gates, or may be implemented as a combination of a general purpose microprocessor and a memory in which a program executable in the microprocessor is stored. It will be appreciated by those skilled in the art that the present invention may be implemented in other forms of hardware.

1, the identification unit 111, the first checking unit 112, and the second checking unit 113 are described separately for convenience of description, and the structure of the processor 110 is shown in FIG. 1 It is not limited.

The communication interface unit 120 receives the compressed data. In other words, the communication interface unit 120 receives the compressed data from the external device. For example, the communication interface unit 120 can transmit / receive data to / from an external device by a wire / wireless communication method. For example, the communication interface unit 120 may transmit and receive data to / from an external device via a data cable connected to the external device. As another example, the communication interface unit 120 may be a wireless network such as the Internet, a LAN (Local Area Network), a Wireless LAN (Local Area Network), a WAN (Wide Area Network) Data can be exchanged with an external device through a wireless communication method such as NFC (Near Field Communication), ZIGBEE, Bluetooth, ultra wide band (UWB) communication, and the like.

The compressed data received by the communication interface unit 120 may be compressed data based on the LZSS algorithm. Hereinafter, an example in which data is compressed based on the LZSS algorithm will be described with reference to FIG.

2 is a diagram for explaining an example in which data according to an embodiment is compressed based on the LZSS algorithm.

Hereinafter, it is assumed that the original string of data to be compressed is " AAAABCAAAB ".

The encoding of the LZSS algorithm is performed through the following procedure.

First, the position (coding position) of the processing point to be encoded is positioned at the start character of the original character string. The characters of length H of the lookahead buffer from the encoding position are stored in the lookahead buffer.

The encoded strings are stored in a search buffer. At the beginning of encoding, since there is no encoded string yet, the search buffer is empty, but the encoded strings are encoded in the search buffer as the encoding progresses. When the search buffer is full, it is removed from the buffer in the order of the longest stored characters.

Looks for a pattern of consecutive characters starting from the start character of the lookahead buffer in the search buffer. If the matching pattern exists in the search buffer and the string length of the pattern is equal to or greater than the threshold value set by the algorithm developer, the offset in the search buffer and the string length (len) information of the pattern are . On the other hand, if the matching pattern does not exist in the search buffer, or if the string length of the pattern is smaller than the threshold value set by the algorithm developer, the start character of the lookahead buffer is output.

After the above-described output is performed, uncompressed characters of length H are newly stored sequentially in the lookahead buffer, and the output character string or character information is sequentially stored in the search buffer in the search buffer. This process is repeated until the lookahead buffer is empty, and compression is completed when the lookahead buffer is empty.

As a result, the compressed data output through the encoding process of the LZSS algorithm is a combination of a single character and (offset, len). In this case, a single character is represented by 8 bits, 'offset' and 'len' are the number of bits represented by the size of the search buffer, the size of the search buffer is S, and the number of bits Is L, the relationship is expressed by the following equation (1).

For example, as shown in FIG. 1, when the size S of the search buffer is 5, since L satisfying Equation (1) is 3, 'offset' and 'len' are represented by 3 bits, respectively.

In the LZSS algorithm, a flag of 1 bit is inserted before the encoding of the original string so as to discriminate whether the bit string read by the decoder in the decoding process signifies a single character (offset, len) do. For example, if a flag bit with a value of 1 is inserted, the next read bit string is a single character and reads 8 bits. On the other hand, if a flag bit with a value of 0 is inserted, the next read bitstream (offset, len) is read and 2 * L bits are read.

Referring again to FIG. 1, the memory 130 stores data used for the error detecting apparatus 100 to operate. For example, the memory 130 may store the compressed data received by the communication interface 120, and the results of error detection derived as the processor 110 operates may be stored.

The processor 110 detects whether or not the compressed data received by the communication interface unit 120 includes an error. Specifically, the processor 110 checks the value of the flag bit included in the compressed data. Then, the processor 110 performs a first check on eight bits after the flag bit in the compressed data when the value of the flag bit is one. Then, the processor 110 performs a second check on the 2 * L bits after the flag bit in the compressed data when the value of the flag bit is zero.

3 to 5, a specific method of detecting whether or not the processor 110 includes an error in the compressed data will be described.

FIG. 3 is a flowchart illustrating an example of a method for detecting whether or not an error is included in compressed data according to an exemplary embodiment.

In step 310, the verification unit 111 confirms the value of the flag bit included in the compressed data. For example, the compressed data may be compressed data based on the LZSS algorithm.

As described above with reference to FIG. 2, the flag bit indicates a bit inserted before the encoding of the original character string. In other words, in the compressed data, a flag bit consisting of one bit is inserted before the bits corresponding to the characters included in the original character string.

Hereinafter, an example of compressed data will be described with reference to FIG.

4 is a view for explaining an example of compressed data according to an embodiment.

FIG. 4 shows an example of compressed data encoded by the LZSS algorithm. Here, f means a flag bit and can be composed of one bit. c means a single character contained in the original string and can be composed of 8 bits. o denotes information on a position of a pattern in the search buffer described above with reference to FIG. 2, and may be composed of L bits. m denotes information on a character string length len of the pattern described above with reference to FIG. 2, and may be composed of L bits.

Referring again to FIG. 3, the confirmation unit 111 reads the flag bits included in the compressed data to check whether the value of the flag bit is 1 or 0. If the value of the flag bit is 1, the confirmation unit 111 can notify the first checking unit 112 of the fact. If the value of the flag bit is 0, the confirmation unit 111 can notify the second checking unit 113 of this.

In step 320, when the value of the flag bit is 1, the first checking unit 112 performs a first check on eight bits after the flag bit in the compressed data. Here, the first check means inspection using a parity bit.

As described above with reference to Fig. 2, the flag bit having a value of 1 means that the bit string (consisting of 8 bits) read after the flag bit is a single character. Accordingly, the first checking unit 112 performs a first check on eight consecutive bits located next to the flag bit.

An error may occur in the process of recording the compressed data on the storage medium or in the process of reading the recorded data. A check using a parity bit may be used to detect the error.

In order to detect an error using a parity bit, first, compressed data is divided into blocks of the same size, and 1-bit parity bits are added in front of each block. If there is an odd number of bits with a value of 1 in the block, add a bit with a value of 1 (parity bit) before the block. If there is an even number of bits having a value of 1 in the block, a bit (parity bit) having a value of 0 is added before the block. Accordingly, the number of bits having a value of 1 in the block including the parity bit can be set to an even number. This process is performed for all blocks.

 The first checking unit 112 reads a bit string on a block-by-block basis including a parity bit and checks whether there is an even number of bits having a value of 1 in the read bit string. If there is an odd number of bits having a value of 1, the first checking unit 112 determines that the compressed data includes an error.

In step 330, when the value of the flag bit is 0, the second checking unit 113 performs a second check on the 2 * L bits after the flag bit in the compressed data.

2 * L bits include information on the position in the search buffer of a character string representing a predetermined pattern in data before compression is performed, and information on the length of the character string. In other words, information on 'offset' is included in the preceding L bits (hereinafter referred to as 'first L bits') of 2 * L bits. The L bits after the 2 * L bits (hereinafter, referred to as 'second L bits') include information on 'len'.

Here, L is a natural number equal to or greater than 1 and can be determined by the size of the search buffer, as described above with reference to Equation (1).

Specifically, the second check performed by the second checking unit 113 is as follows.

First, the second checking unit 113 checks whether the value indicated by the first L bits is greater than or equal to the value indicated by the second L bits. The second checking unit 113 checks whether the value indicated by the first L bits is smaller than or equal to a value corresponding to the size of the search buffer. The second checking unit 113 checks whether the value indicated by the second L bits is less than or equal to a value corresponding to the size of the lookahead buffer.

If the value represented by the first L bits is greater than or equal to the value represented by the second L bits and the value indicated by the first L bits is less than or equal to a value corresponding to the size of the search buffer, Is less than or equal to a value corresponding to the size of the lookahead buffer, the second checking unit 113 determines that there is no error in the compressed data.

Since the data compressed by the LZSS algorithm has characteristics to be described later, the first checking unit 112 and the second checking unit 113 can detect whether the compressed data includes an error.

1) If the value of the flag bit is 1, the following bits mean a single character 'c'. This single character consists of 8 bits and is represented by ASCII code (ASCII). Of the 8 bits, 7 bits are used to represent a single character among 128 expressible characters, and the remaining 1 bit is used for parity checking.

2) When the value of the flag bit is 0, the following bits mean a pair of (offset, len), and each consists of L bits, totaling 2L bits. Where 'offset' is always greater than or equal to 'len'. This is because the length of the matching string 'len' in the search buffer and the lookahead buffer must be less than or equal to 'offset', which indicates the start position of the matching string in the search buffer. Therefore, if there is no error in the data compressed by the LZSS algorithm, 'offset' and 'len' in a pair always have to satisfy the following condition (2).

3) The value of 'offset' should always be less than or equal to the size of the search buffer. Because the matching string is found in the search buffer, the starting position of the matching string can not be farther than the size of the search buffer. Therefore, if there is no error in the data compressed by the LZSS algorithm, the value of 'offset' should always satisfy the following condition (3).

4) The value of len should always be less than or equal to the size of the lookahead buffer. Because the matching character string is found in the lookahead buffer, the size of the matching character string can not be larger than the size of the lookahead buffer. Therefore, if there is no error in the data compressed by the LZSS algorithm, the value of 'len' should always satisfy the following condition (4).

The above-mentioned 1) -4) is characteristic of the compressed data encoded by the LZSS algorithm.

1), if the flag bit is 1, an error can be detected by performing parity check on the following 8 bits. 2) -4), if any one of Equations (2), (3) and (4) is not satisfied, it is found that an error has occurred in the compressed data encoded by the LZSS algorithm.

5 is a flow diagram illustrating an example of the operation of a processor in accordance with one embodiment.

The method shown in the flowchart of FIG. 5 is comprised of steps that are processed in a time-series manner in the processor 110 shown in FIG. Therefore, it will be understood that the contents described above with respect to the processor 110 shown in FIG. 1 apply to the method shown in the flowchart of FIG. 5, even if omitted from the following description.

In steps 511 and 512, the confirmation unit 111 reads from the first bit of the compressed data and confirms the value of the flag bit. If the value of the flag bit is 1, the process proceeds to step 521, and if the value of the flag bit is 0, the process proceeds to step 531. [

In steps 521 and 522, the first checking unit 112 reads eight bits following the flag bit and checks the parity bit.

In step 523, the first checking unit 112 checks whether a parity error has been detected. An example in which the first checking unit 112 confirms the detection of the parity error is as described above with reference to FIG. If a parity error is detected, the process proceeds to step 542, and if a parity error is not detected, the process proceeds to step 524.

In step 524, the first checking unit 112 checks whether the lookahead buffer is empty. If the lookahead buffer is empty, the process proceeds to step 543. Otherwise, the process proceeds to step 511. [

In steps 531 and 532, the second checking unit 113 reads the 2 * L bits following the flag bit, and divides the 2 * L bits into the first L bits and the second bits. Here, the first L bits include information on 'offset', and the second L bits include information on 'len'.

In step 533, the second checking unit 113 determines whether the value o indicated by the first L bits is greater than or equal to the value m indicated by the second L bits. If the value o indicated by the first L bits is greater than or equal to the value m indicated by the second L bits, the process proceeds to step 534. Otherwise, the process proceeds to step 542. [

In step 534, the second checking unit 113 determines whether the value o indicated by the first L bits is less than or equal to a value S corresponding to the size of the search buffer. If the value o indicated by the first L bits is less than or equal to the value S corresponding to the size of the search buffer, the process proceeds to step 535. Otherwise, the process proceeds to step 542. [

In step 535, the second checking unit 113 determines whether the value m indicated by the second L bits is less than or equal to a value H corresponding to the size of the lookahead buffer. If the value m indicated by the second L bits is less than or equal to the value H corresponding to the size of the lookahead buffer, the process proceeds to step 536. Otherwise, the process proceeds to step 542. [

In step 536, the second checking unit 113 checks whether the lookahead buffer is empty. If the lookahead buffer is empty, the process proceeds to step 541. Otherwise, the process proceeds to step 511. [

In steps 541 and 543, it is determined that there is no error in the data compressed by the LZSS algorithm.

In step 542, it is determined that there is an error in the data compressed by the LZSS algorithm.

The processor 110 may perform error detection of the LZSS compressed data according to the method described above with reference to FIG. Then, under the assumption that no error has occurred in the LZSS compressed data, the processor 110 determines whether or not the compressed data with an arbitrary compression algorithm is data compressed with the LZSS algorithm through the method described above with reference to Fig. 5 It is possible.

According to the above description, the error detecting apparatus 100 can perform error detection on data compressed with the LZSS algorithm without additional bit insertion. Further, on the assumption that no error has occurred, the error detecting apparatus 100 can determine whether or not the compressed data is compressed with the LZSS algorithm for the compressed data.

Meanwhile, the above-described method can be implemented in a general-purpose digital computer that can be created as a program that can be executed by a computer and operates the program using a computer-readable recording medium. In addition, the structure of the data used in the above-described method can be recorded on a computer-readable recording medium through various means. The computer-readable recording medium includes a storage medium such as a magnetic storage medium (e.g., ROM, RAM, USB, floppy disk, hard disk, etc.), optical reading medium (e.g. CD ROM, do.

It will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims. Therefore, the disclosed methods should be considered from an illustrative point of view, not from a restrictive point of view. The scope of the present invention is defined by the appended claims rather than by the foregoing description, and all differences within the scope of equivalents thereof should be construed as being included in the present invention.

100: Error detection device
110: Processor
111:
112: First inspection section
113:
120: Communication interface unit
130: memory

Claims (12)

A method for detecting whether or not an original string contains an error in compressed compressed data,
Confirming a value of a flag bit included in the compressed data;
Performing a first check on the eight bits after the flag bit in the compressed data if the value of the flag bit is one; And
And performing a second check on 2 * L bits after the flag bit in the compressed data if the value of the flag bit is 0,
Wherein L is a natural number equal to or greater than 1 and is determined by a size of a search buffer in which at least one character encoded in advance is stored among characters included in the original character string. The method according to claim 1,
The second test may include:
Determining whether a value represented by the preceding L bits of the 2 * L bits is greater than or equal to a value represented by the following L bits;
Checking whether the value indicated by the preceding L bits is less than or equal to a value corresponding to the size of the search buffer; And
Determining whether a value indicated by the L bits after the L is less than or equal to a value corresponding to a size of a lookahead buffer,
The value corresponding to the size of the search buffer means the maximum number of characters that can be stored in the search buffer,
Wherein the lookahead buffer is a buffer in which at least one character that is currently encoded is stored among characters included in the original character string, and a value corresponding to the size of the lookahead buffer is a character that can be stored in the lookahead buffer ≪ / RTI > The method according to claim 1,
Wherein the first check includes checking using a parity bit. The method according to claim 1,
Wherein the 2 * L bits include information on a position in the search buffer of a character string representing a predetermined pattern in the original character string and information on a length of a character string representing the predetermined pattern. The method according to claim 1,
Wherein the compressed data comprises compressed data based on an LZSS algorithm. The method according to claim 1,
And receiving the compressed data. A computer-readable recording medium recording a program for causing a computer to execute the method of claim 1. An apparatus for detecting whether or not an original string contains an error in compressed compressed data, the apparatus comprising:
A communication interface for receiving the compressed data; And
A first check is performed on 8 bits after the flag bit in the compressed data when the value of the flag bit is 1, And performing a second check on 2 * L bits after the flag bit in the compressed data when the value of the flag bit is 0,
Wherein L is a natural number equal to or greater than 1 and is determined by a size of a search buffer in which at least one character encoded in advance is stored among characters included in the original character string. 9. The method of claim 8,
The processor comprising:
Determining whether a value indicated by the preceding L bits of the 2 * L bits is greater than or equal to a value represented by the following L bits, and if the value represented by the preceding L bits corresponds to the size of the search buffer Value and checking whether the value indicated by the following L bits is less than or equal to a value corresponding to the size of the lookahead buffer,
The value corresponding to the size of the search buffer means the maximum number of characters that can be stored in the search buffer,
Wherein the lookahead buffer is a buffer in which at least one character that is currently encoded is stored among characters included in the original character string, and a value corresponding to the size of the lookahead buffer is a character that can be stored in the lookahead buffer ≪ / RTI > 9. The method of claim 8,
Wherein the first check includes checking using a parity bit. 9. The method of claim 8,
Wherein the 2 * L bits include information on a position in the search buffer of a character string representing a predetermined pattern in the original character string, and information on a length of a character string indicating the predetermined pattern. 9. The method of claim 8,
Wherein the compressed data comprises compressed data based on an LZSS algorithm.

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