JPH05250137A - Data compressing/restoring system - Google Patents

Abstract

PURPOSE:To improve the processing reliability of a data compressing/restoring system by deciding whether the data used for the data compressing/restoring processing are normal or wrong. CONSTITUTION:A compressing part 2 receives the data and retrieves a dictionary 3 by an external hash method to compress the input data and to output the coded data. At the same time, a maximum application address holding part 7 holds the maximum value of the address used by the dictionary 3. In a dictionary retrieving state, a comparing part 6 compares the retrieved address value with the address value of the part 7. Then the execution of the normal processing is decided if the retrieved address value is smaller than the maximum application address value. If not, an invalid retrieving state is decided and an error signal is outputted to interrupt the processing under execution. Furthermore the maximum application address value is always updated when the normal processing is carried on and then newly registered in the dictionary 3.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention compresses various data,
Alternatively, it relates to a data compression and decompression method used when decompressing.

(Background of Technology) In recent years, various kinds of data such as character codes, vector information, and images have been handled by computers, and the amount of data handled has been increasing rapidly. When handling a large amount of data, omit redundant parts in the data and compress the amount of data,
You can reduce the storage capacity and transfer faster.

Universal encoding has been proposed as a method of compressing various data by one method.
Here, the field of the present invention is not limited to compression of character codes,
Although it can be applied to various data, in the following, the word used in information theory will be followed, and one word unit of data will be referred to as a character, and data connected in arbitrary words will be referred to as a character string.

As a typical method of the universal code,
There is a Ziv-Lempel code (for details, see
For example, see Munakata "Ziv-Lempel Data Compression Method", Information Processing, Vol.26, No.1, 1985). In Ziv-Lempel code, universal type and incremental decomposition type (Incremental pa
rsing) two algorithms have been proposed.

Further, as an improvement of the universal type algorithm, there is LZSS code (TC Bell, "Better O.
PM / L Text Compression ", IEEE Trans. On Commun., V
ol, COM-34, No. 12, Dec. 1986). As an improvement of the incremental decomposition type algorithm, LZW (Lempel-Ziv-W
elch) Signed (TA Welch, "A Technique for Hig
h-Performance Data Compression ", Computer, June 19
84).

Among these codes, the LZW code has come to be used for file compression of the storage device because of its high-speed processing and the simplicity of the algorithm.

[0007]

8 to 19 are views showing a conventional example, FIG. 8 is a data compression / decompression device, FIG. 9 is an LZW encoding processing flowchart, FIG. 10 is an LZW decoding processing flowchart, and FIG. A is an explanatory diagram of a specific example of LZW encoding,
11B is an explanatory diagram of a dictionary configuration example, FIG. 12 is an explanatory diagram of a specific example of LZW decoding, FIG. 13 is an explanatory diagram of a list structure of the external hash method, FIG. 14 is a configuration example of a dictionary memory (when encoding),
15 is an explanatory diagram of a dictionary (at the time of encoding), FIG. 16 is a flowchart of LZW encoding processing by the external hash method, and
Is a configuration example of the dictionary memory (at the time of restoration), FIG. 18 is an explanatory diagram of the dictionary (at the time of restoration), and FIG. 19 is a flowchart of the LZW decoding process by the external hash method.

In the figure, 1 is a data compression device, 2 is a compression unit (data compression unit), 3 is a dictionary unit, 4 is a data decompression device,
Reference numeral 5 denotes a restoration unit (data restoration unit). (1) Description of equipment used in conventional data compression / decompression processing
.. See FIG. 8 FIG. 8 shows an example of the data compression / decompression device used in the data compression / decompression process by the encoding / decoding described below.

The compression device 1 shown in FIG. 8A is provided with a compression unit 2 for performing data compression processing by encoding and a dictionary unit 3 used for encoding. Further, the restoration device 4 shown in FIG. 8B is provided with a restoration unit 5 that performs a data restoration process by decoding and a dictionary unit 3 that is used at the time of decoding.

(2) Description of encoding / decoding process by LZW code ... See FIGS. 9 to 12. First, the LZW encoding process has a rewritable dictionary,
The input character string is divided into different character strings (substrings), reference numbers are assigned to the character strings in the order in which they appear, and they are registered in the dictionary, and the currently input character string is registered in the dictionary. It is represented by the reference number of the longest matching character string and encoded.

FIG. 11A is an explanatory diagram of LZW encoding, FIG. 12 is an explanatory diagram of LZW decoding, and FIG.
B shows a dictionary configuration example created at the time of encoding and decoding. Note that, in FIGS. 11 and 12, for simplification of description, an example of compressing and decompressing data consisting of a combination of three letters abc is taken.

In the LZW encoding process of FIG. 9, first, in step S1, a character string consisting of one character for every character is registered in the dictionary in advance as an initial value, and then encoding is started. In the encoding in step S1, the dictionary is searched by the input first character K to obtain the reference number ω, which is used as the initial character string.

Next, in step S2, the next character K of the input data is read, and in step S3, it is checked whether or not the character input is completed. Then, the process proceeds to step S4 and step S1.
It is searched whether or not there is an extended character string (ωK) obtained by adding the character K read in step S2 to the initial character string ω obtained in step S2.

If the character string (ωK) is not in the dictionary in step S4, the process proceeds to step S6, the reference number ω of the character K obtained in step S1 is output as the code word code (ω), and the character string (ωK) is also output. , A new reference number is added and registered in the dictionary, the input character K in step S2 is replaced with the reference number ω, the dictionary address n is incremented, and the process returns to step S2 to read the next character K.

On the other hand, if the character string (ωK) is found in the dictionary at step S4, the character string (ωK) is referred to as reference number ω at step S5.
, And returns to step S2 again, and in step S4, the search for the maximum matching length is continued until the character string (ωK) cannot be searched from the dictionary.

The LZW coding will be described in detail with reference to FIG. First, the input data of FIG. 11A
Input is read from left to right. When you enter the first letter a, there is no matching string in addition to the letter a in the dictionary, so
OUTPUT CODE 1 (reference number ω) is coded and output.
Then, let the character a be the initial character string ω.

Next, if the second character b is input,
Extended character string ωK = which adds this input character to the initial character string ω
Since ab is not in the dictionary, OUTPUT CODE 2 of the character b is output as a code word. Then, the extended character string ωK = ab
Is added to the dictionary with reference number 4. The actual dictionary registration is registered as a character string 1b as shown on the right side of FIG. 11B. Then, the character b becomes the initial character string ω.

If the third character a is subsequently input, an extended character string ωK = b obtained by adding the initial character string ω to the character b.
Since a = 2a is not in the dictionary, the OUTPUT CODE of the character a
After outputting 1 as a code word, the extended character string ωK = ba is represented by 2a, and the reference number 5 is attached to register it in the dictionary. Then, the character a becomes a new initial character string ω.

For the fourth input character b, the extended character string ωK = ab is already registered in the dictionary as the code word 4 of 1b, so the character string ωK is set as a new initial character string ω.
The second character c is input and the extended character string ωK = 4c = abc
make. Since the extended character string ωK = abc is not registered in the dictionary, OUTPUT CODE4 of the character string ab = 1b
Is output as a code word, and the extended character string ωK = abc is registered in the dictionary as code word 6 in the form of 4c. This process is continued in the same manner thereafter.

The decoding process of FIG. 10 performs the reverse operation of the encoding of FIG. In the LZW decoding of FIG. 10, similarly to the case of encoding, a character string consisting of one character for every character is registered in the dictionary in advance as an initial value and then decoding is started.

First, in step S1, the first code (reference number) is read, the current CODE is set to OLD code, and the first code corresponds to any one-character reference number already registered in the dictionary. The matching character code
Find (K) and output the letter K.

The output character K is for exception processing later.
Set to FINchar. Next, in step S2, the next code is read and set as CODE in INcode.
In step S3, it is checked whether or not there is a new code, that is, whether or not the code input is completed, and the process proceeds to step S4. It is checked whether or not the code CODE input in step S3 is defined (registered) in the dictionary. ..

Since the input code word is normally registered in the dictionary by the processing up to the previous time, the process proceeds to step S5 and the code is input.
The character string code (ωK) corresponding to CODE is read from the dictionary, the character K is temporarily stacked in step S6, and the reference number CODE (ω) is used as a new code CODE again in step S6.
5, the procedure of steps S5 and S6 is recursively repeated until the reference number ω reaches one character K, and finally, the process proceeds to step S7 and the characters stacked in step S6 are written in LIFO (Last In Fast Out) format. Pop up and output.

At the same time, in step S7, the code ω used last time and the first character K of the character string restored this time are combined (ω
A new reference number is added to the character string expressed as (K) and registered in the dictionary.

The LZW decoding process will be described in detail with reference to FIG. First, in FIG. 10, the first input codeword (INPUT CODE) is 1, and one character a, b, c
11 is already registered in the dictionary as reference numbers 1, 2, and 3 as shown in FIG. 11B, and therefore is output by replacing it with the character string a having the reference number that matches the codeword 1 by referring to the dictionary.

Similarly for the next code word 2, the character b
Replace with and output. Code word 1 processed last time
A new reference number 4 is added to the character string ωK = 1b, which is a combination of the first character b of the character string decoded this time, and registered in the dictionary.

The third code word 4 replaces the character string 1b obtained by the dictionary search with the character string ab and outputs the character string ab. At the same time, a character string ωK = 2a obtained by combining the previously processed code word 2 and the first character a of the character string decoded this time
A new reference number 5 is added to (= ba) and registered in the dictionary.

Similarly, this process is repeated. 12
There are the following exceptions in the decryption of. This exception processing occurs in the decoding of the sixth input code 8. Code 8 is not defined in the dictionary at the time of decoding and cannot be decoded. In this case, a character string 5b obtained by adding the first character b of the previously decoded character string ba to the code 5 processed last time is further calculated as 2a
It is replaced with b and bab and output.

Then, the previous code word 5 is added to the output word of the character string.
The reference number 8 is added to the character string 5b obtained by adding the character b of the character string decoded this time, and registered in the dictionary. This exception process is performed through the processes of S4 and S8 in the decoding process flow of FIG. 10, and finally is performed in S7 in which the character string is output and the new character string is added to the reference number and registered in the dictionary S7.

The encoding / decoding processing of FIGS. 9 and 10 is performed while creating the same dictionary. When the encoding is performed according to the procedure shown in the flowchart of FIG. 9, it takes a long time because the entire dictionary must be searched every time one character string is searched for in the dictionary. Therefore, in the past, an external hash method (open hashing, or chaining) was used in the dictionary search to increase the processing speed (see, for example, Ohmsha, IPSJ, Information Processing Handbook). Next, the external hash method will be described.

(3) Description of the external hash method ... FIG.
Referring to FIG. 19, when considering a set S of character strings, it is possible to perform a high-speed search if the position of the character string x of S is directly calculated as the address of the storage position of the character strings x to x.
The hash method realizes this.

If addresses 0 to m-1 are given to the storage location (hash table), the function h: S → [0, 1, ... Then, the address of the character string x of S is obtained by h (x). The function h is a hash function, and the value h (x) is a hash of x.
It is called an address.

The hash method is usually used when the size of S is much larger than m. Therefore, no matter how h is selected, different character strings x1, x of S
It is possible that h (x1) = h (x2) for 2. This is called a collision, and an external hashing method (open hashing or chaining) is used as one of the countermeasures against the collision.

An outline of the compression / decompression process of the LZW code using the external hash method will be described below for the dictionary search. For details, see, for example, "AP-Labo, Hard Disk Cookbook, Shoeisha Publishing Co., 1987. "checking.

In the external hash method, as shown in FIG. 13, a linked list is prepared for each hash address i indicated by an index (directory), and a character string x of a hash address h (x) = i at which a collision occurs is generated. Are stored in order from the beginning of the linked list.

Each linked list having the same hash address h (x) is called a bucket. Description of Encoding Process by External Hash Method ... FIG. 14
See FIG. 16. In this external hash method, as shown in FIG.
By searching the index part with a hash address, the corresponding list is shown. Further, each list stores identification information corresponding to each element and a pointer indicating the storage location of the next element. In this way, the elements having the same hash address are linked by the index and the list, and the elements can be sequentially searched.

For example, the above-mentioned reference number ω is used as a hash address, and the head address of a list for storing a partial sequence in which one character is added to the partial sequence corresponding to the reference number ω is stored in this hash address. In addition, a partial sequence corresponding to the node corresponding to the “child” of the node corresponding to the reference number ω described above may be sequentially stored in the corresponding list. In this way, the connection relationship between the candidate elements represented by the combination of the reference number ω and the one letter K may be shown. In this case, the extended character K of each element may be stored in the list as the corresponding identification information.

The dictionary used for encoding by the external hash method is constructed as shown in FIGS. 14 and 15. This dictionary includes "first", "next", "ext"
There is each item (array) of (extention). The first
13 corresponds to the index part of FIG. 13, and next and ext correspond to the list of FIG.

This dictionary can be expressed as shown in FIG.
That is, centered on ext (representing the extended character), the address is at the upper left, the first is at the lower left, and the
Display next (displayed like this for convenience of explanation).

Then, as shown in FIG.
It is represented by each layer of 1, # 2, # 3, # 4 ... (Layer according to the order of the character strings), and has a “tree structure” as a whole.

In this dictionary, the storage address of the extended character is shown in "address", and the start address of the next character is shown in "first". The addresses of the same layer are shown in "next". Therefore, the dictionary is used by using this information.

Next, the outline of the encoding process using the external hash method will be described with reference to FIG. LZW of FIG. 16
The encoding process will be described below by taking as an example the case where three characters A, B, and C are used to simplify the description.

First, in step S1, the following initialization processes 1 to 3 are performed. Initialize the dictionary to include the first character. Here, since the three letters of the alphabet A, B, and C are targeted, the character codes of A, B, and C are directly used as hash addresses, and the addresses 1, 2 of the dictionary memory in FIG.
Register to 3.

The number n of characters currently registered in the dictionary is set to the number of registered characters. In the case of three letters of the alphabet, n = 3. The first input character K is the initial letter string i. In this case, since the first input character is "A", the initial character string i = 1.

The dictionary search array is initialized to 0. That is, the search sequence for the first, next and extended characters is
Since it is represented by first [1, Nmax], next [1, Nmax], and EXT [1, Nmax], this is initialized to 0.

When the initialization process in step S1 is completed, the process proceeds to step S2, and as a result, it is assumed that the dictionary shown in FIGS. 14 and 15 is currently created.

The process for inputting and encoding the character string "AAAA" in this state will now be described. Since the initialization of step S1 has been completed, the first input character “A” is set to the initial character string ω = 1, the first input character “A” is set to the initial character string ω = 1 in step S1, and step S2 Read the second input character "A" with. Then, in step S3, it is determined that there are unprocessed characters, and steps S5 to S
Proceed to the dictionary search step shown in FIG.

In the dictionary search step, first, step S5
And set the initial character string ω = 1 to the variable i as i = 1,
And the variable j is set to j = 0. Where variable i is an array
It is the address value of the dictionary memory specified by the stored value of first, and the variable j is the address value of the dictionary memory specified by the stored value of next.

Next, in step S6, the contents of the address 1 of the dictionary memory of FIG. 14 designated by the variable i are read, "A" is read from ext as a symbol (smbol), and firs
The next address "4" is read from t and the variable i = 4 is set.

Then, in step S7, it is checked whether or not i = 0 to determine whether or not to move to the dictionary registration step. Since i = 4 at this time, the process proceeds to step S8, and the address in step S6 is entered. It is determined whether the symbol "A" obtained by referring to ext of 1 and the first input character "A" match. In this case, since they match, the process returns to step S2 to read the third input character "A".

Then, through step S3, step S5
Then, the address i of the dictionary memory is set to the value i = 4 of the variable i at that time, and the address 4 of the dictionary memory is referred to. Next, in step S6, the contents of address 4 in the dictionary memory are read, "B" is read as the symbol (smbol) stored in ext, and the address from the first to the next address "6"
Is read and set to the variable i = 6.

Then, in step S7, it is checked whether i = 0. Since i = 6 at this time, step S7 is executed.
In step S8, it is determined whether the symbol "B" obtained from ext at address 4 in step S6 matches the input character "A" obtained in step S2. In this case, since they do not match, the process proceeds to step S9.

In step S9, a variable i is set to a value of j = 10 obtained from next by referring to the address 4 of the dictionary memory to set i = 10. This replacement of the variable i with the variable j is to make it possible for the variable j as well, since the determination in step S7 is made only for the variable i.

Next, referring to the address 10 of the dictionary memory designated by the variable i which has been replaced, the address 10
The symbol "A" stored in ext is read, and the next address value 11 stored in the first address 10 is set in the variable i.

Next, returning to step S7, at this time i = 1
Since it is 1, the address 10 obtained in step S9
The symbol "A" is compared with the input character "A", and since they match, the process proceeds to step S2 and the process of the third character is performed.

The same processing as that of the first input character is performed for the third and fourth input characters "A", and the addresses 10 to 11 and the addresses 11 to 12 of the dictionary memory are further processed.
When the processing of the address 12 is completed, there is no character to be processed in step S3, and therefore the processing proceeds to step S16, where the final address ω = 12 is output as the code {code (ω)} and the series of processing is completed.

Next, the processing of the dictionary registration step of steps S11 to S15 will be described. The dictionary is registered when i = 0 in the first or next search in the dictionary search step.

That is, when i = 0 is determined in step S7, the dictionary search can no longer be performed, so in step S10 the dictionary address ω at that time is output as the code {code (ω)} and the dictionary registration step is entered.

In the dictionary registration step, first, step S1
At 1, the number n of characters currently registered in the dictionary memory at that time is set to the variable i, and n is further incremented by 1. Then, in step S12, it is checked whether or not j = 0. If j = 0, i = 0. Therefore, the process proceeds to step S13 and firs
Register t. If j = 0, the process proceeds to step S14 to perform next registration processing.

In the first registration processing of step S13, the value (n + 1) indicating the next registration destination is stored in the first of the memory address n designated by the i counter, and the value is input to the ext of the next memory address (n + 1). Register the letter K as a symbol.

Specifically, taking the case where the input character "A" is registered following the address 11 in FIGS. 14 and 15, as an example, the next registration destination in the first of the memory address 11 specified by the variable i. Is stored, and the input character “A” is registered as a symbol in ext of the next memory address 12.

On the other hand, in the next registration processing of step S14, the value of (n + 1) indicating the next registration destination is stored in the next of the memory address designated by the variable i, and the next memory address (n + 1) is stored. Register the input character K as a symbol in ext.

Specifically, taking as an example the case where the input character "A" is registered at the address 10 in FIGS. 14 and 15, first, in the next of the memory address 4 designated by the variable i, the next
The address value 10 indicating the registration destination of is stored, and the input character “A” is registered as a symbol in ext of the memory address 10.

When the above registration process is completed, the registered character K is set in the variable i and the process returns from step S2 to the dictionary search step. Description of Decoding Process by External Hash Method ... FIG. 17
See FIG. 19. In the decryption process by the external hash method, FIGS.
Use the dictionary shown in. In this dictionary, "before" and "ex
The item (array) of "t" is used.

"Before" is the address (fi
The reverse of rst) is shown, and the dictionary is searched using this before. This dictionary is displayed as shown in FIG. As shown, the address is shown in the upper left of ext (extended character),
The bottom left shows before.

Next, the decryption process by the external hash method will be described with reference to the process flowchart of FIG. In FIG. 19, initialization of steps S1-1 and S1-2 is the same as the process S1 of FIG. 10 except that before and ext are initialized as the dictionary search array.

Further, the restoration process by the dictionary search in steps S2 to S8 is basically the same as the process in FIG. For example, in the dictionary shown in FIGS. 17 and 18, the codeword code 1
To restore 2, do the following: First code = 1
Ex by referring to the address 12 of the dictionary memory specified by 2
The symbol "A" of t is read and stacked.

Next, the next address 11 is read from before (read in the direction of the arrow in FIG. 18). By repeating the same processing thereafter, the ext symbol “AAA” at addresses 11, 10, and 1 is read and stacked, and at the address 1, the next memory address becomes 0 and the minimum value NMI is reached.
Since the number is equal to or less than N, the symbol string "AAA" that has been stacked until then is output as a restored character string.

In addition to such a dictionary search, step S
The dictionary is registered at 7. This dictionary registration is performed one step behind the restoration of the symbol, and after outputting the restored character string, the first character obtained by restoring the next code word is stored in the memory address of the currently registered number of characters n. Register in before and symbol in ext.

[0070]

SUMMARY OF THE INVENTION The above-mentioned conventional device has the following problems. (1) The conventional data compression / decompression method is based on the premise that no hardware error occurs during processing.

Therefore, for example, if an error occurs in the communication path, the data to be processed is affected and normal processing cannot be performed. (2) The data compression / decompression process using the conventional LZW code is
While creating a dictionary on the area secured in the memory, the dictionary is used for processing.

In this case, the contents of the dictionary are composed of a linked list, and these lists are followed when searching the dictionary. However, in the case of being configured as a data compression / decompression device, the dictionary memory may be destroyed or the data may be corrupted.

In this case, in the conventional encoding / decoding process using the LZW code, even if erroneous data is read out and used, it is not possible to judge whether it is legitimate data or erroneous data. could not.

The present invention solves such a conventional problem, and makes it possible to judge whether the data used for the data compression / decompression process is regular data or erroneous data. The purpose is to increase reliability.

[0075]

FIG. 1 is a principle diagram of the present invention. FIG. 1A shows a principle diagram (1) and FIG. 1B shows a principle diagram (2).

In FIG. 1, the same symbols as those in FIG. 8 indicate the same components. Further, 6 indicates a comparison unit, and 7 indicates a maximum used address holding unit. The present invention has the following configuration to solve the above problems.

(1) The data compression unit 2 and the dictionary unit 3 are provided, and the dictionary unit 3 divides the encoded data into different subsequences, and a different reference number (ω ) Is added and registered, and the compression unit 2 uses the external hash method to search the dictionary unit 3, and the input data is the reference number of the substring registered in the dictionary unit 3 that has the maximum length match. In the data compression method in which the encoding is performed by designating with (ω), an information holding unit that holds information indicating that the partial sequence is registered in the dictionary unit 3, and the information when the dictionary unit 3 searches When a determination unit that determines whether or not the registered region held in the holding unit is searched is provided, and it is determined by the determination by the determination unit that a region other than the registered region is searched, , It was detected as an error.

(2) The information holding means of the above configuration (1) is configured by the maximum used address holding unit 7 that holds the maximum address value registered in the dictionary unit 3. (3) The determination means of the above-mentioned configuration (1) is composed of the address value used in the search of the dictionary unit 3 and the maximum use address holding unit 7
The comparison unit 6 compares the address value held in the.

(4) If the address value used in the search of the dictionary unit 3 is larger than the address value held in the maximum used address holding unit 7 by the comparison of the comparing unit 6 of the above configuration (3), it is invalid. The process was interrupted as a search.

(5) The data restoration section 5 and the dictionary section 3 are provided. The dictionary section 3 divides the coded data into different subsequences, and a different reference number (ω ) Is added and registered, and in the restoring unit 5, the predetermined data is coded by designating the predetermined data with the reference number (ω) of the substring registered in the dictionary unit 3 having the maximum length match. In the data restoration method of restoring the original subsequence data by searching the dictionary unit 3 using the external hash method based on the input data. Information holding means for holding information indicating the registered area in 3 and determination means for judging whether or not the registered area held in the information holding means is searched at the time of searching the dictionary unit 3. Is provided, and the area other than the registered area is searched by the judgment by the judgment means. If it is was detected as an error.

(6) The information holding means of the above configuration (5) is configured by the maximum used address holding unit 7 that holds the maximum address value registered in the dictionary unit 3. (7) Comparison in which the determination unit of the above configuration (5) compares the address value used in the search of the dictionary unit 3 with the address value held in the maximum used address holding unit 7 of the above configuration (6) It is composed of part 6.

(8) If the address value used in the search of the dictionary unit 3 is larger than the address value held in the maximum used address holding unit 7 as a result of the comparison of the comparing unit 6 in the above configuration (7), it is invalid. The process was interrupted as a search.

[0083]

The operation of the present invention based on the above construction will be described with reference to FIG. (1) Operation of data compression method: See the data compression device in FIG. 1A. When data is input, the compression unit 2 searches the dictionary unit 3 by the external hash method and compresses the input data (encoding process). And outputs encoded data.

At this time, the maximum use address holding unit 7
The maximum value of the address used in the dictionary unit 3 (address value 10 in the example of FIG. 1A) is held. Then, at the time of dictionary search, the comparison unit 6 compares the search address value with the address value of the maximum used address holding unit 7.

As a result, if the search address value is less than or equal to the maximum used address value, it is determined that normal processing is being performed, and if the search address value is greater than the maximum used address value, it is determined that the search is invalid. , Output an error signal,
Suspend processing.

When normal processing is performed,
When newly registering in the dictionary, the maximum use address value is constantly updated. While repeating the above processing,
Performs data compression processing.

As described above, the maximum used address of the currently registered dictionary is held, and data compression is performed while confirming that the address of the dictionary used for the search is in use. It is possible to detect an error due to destruction or the like.

(2) Operation of data restoration process ... See data restoration device in FIG. 1B. When data is input, the restoration unit 5 searches the dictionary unit 3 by the external hash method to restore the input data. , Output the restored data.

Even when such data is restored, the maximum used address holding unit 7 holds the maximum value of the address used in the dictionary unit 3 (address value 10 in the example of FIG. 1B).

Then, as in the case of data compression, the comparison unit 6 compares the address values and detects an error from the comparison result. Thus, by performing the data restoration process while confirming that the address of the dictionary used for searching the dictionary is in use, it is possible to detect the invalidity of the process due to the destruction of the address pointer of the dictionary.

[0091]

Embodiments of the present invention will be described below with reference to the drawings. (Description of First Embodiment) FIGS. 2 to 6 are views showing a first embodiment of the present invention, FIG. 2 is a view showing a data compression / decompression device, and FIG. 3 is a data compression processing flowchart ( Part 1), FIG. 4 is a data compression processing flowchart (Part 2), FIG. 5 is a data decompression processing flowchart (Part 1), and FIG. 6 is a data decompression processing flowchart (Part 2).
Is.

2 to 6, the same symbols as those in FIG. 1 indicate the same components. (1) Description of data compression / decompression device--see FIG. 2 The data compression device in the first embodiment is shown in FIG. 2A, and the data decompression device is shown in FIG. 2B.

In this example, the data compressing device 8 is provided with the compressing unit 2, the dictionary unit 3, the maximum use address holding unit 7, and the comparing unit 6, and the data restoring device 9 is provided with the restoring unit 5, the dictionary unit 3, and the maximum use unit. An address holding unit 7 and a comparison unit 6 are provided.

The compression unit 2, the decompression unit 5, and the dictionary unit 3 of the above configuration are the same as those of the conventional example. The maximum use address holding unit 7 holds a maximum address (for example, a memory) of the storage addresses of the data registered in the dictionary unit 3 (addresses of the dictionary memory actually used).

The comparison unit 6 includes the compression unit 2 or the decompression unit 5.
Is to compare the address (search address) used when searching the dictionary unit 3 with the value (maximum address) stored in the maximum used address holding unit 7.

As a result of the comparison by the comparison unit 6, the address (dictionary memory address) used for searching the dictionary unit 3 becomes
If it is less than the maximum used address, it is judged that it is currently being used (normal state), and if the address used for searching exceeds the maximum used address, an error due to destruction of the address pointer in the dictionary, etc. As a state,
An error signal is output from the comparison unit 6.

By such processing, when data is compressed,
Alternatively, when processing is performed using erroneous data at the time of restoration, it is possible to detect (due to the error signal) during the processing.

Data compression processing and data decompression processing by the apparatus having the above configuration will be described below with reference to FIGS. (2) Description of processing during data compression-See Figs. 3 and 4 During data compression, input data is converted into encoded data by the external hash method and output, but incorrect data is used during the process In order to monitor whether or not the search address has been searched, the search address and the maximum used address are compared at the time of dictionary search.

The processing at the time of data compression will be described below with reference to the processing flowcharts of FIGS. The process numbers in the figure are shown in parentheses. First, at the beginning of the process,
Initialize the dictionary to include the first character (S
1).

In this case, for example, if a dictionary as shown in FIGS. 14 and 15 is used and the characters used are three characters A, B, and C, the character codes of the three characters A, B, and C are directly used as the hash address in the dictionary. Register in memory addresses 1, 2, and 3 (register character code i in dictionary address i).

Further, the reference number given to the substring to be registered next is set to the currently registered character string n in the dictionary. For example, the reference number "1" given to the letters A, B, C,
“2” and “3” are stored in the dictionary as hash addresses, and a numerical value may be set in the current registered character string n (n → NM
IN). Here, the maximum value of the subsequence that can be registered in the dictionary is N
MAX, an array fi consisting of NMAX components
rst, array next and array ext are defined, and the initial value 0 is set to all the components of these arrays.

The array first corresponds to the index part, and the array
The next and array ext correspond to the list (see FIG. 13). Therefore, in the i-th component first (i) of the array first, the array ne at the beginning of the list corresponding to the node with the reference number i
A number indicating the component of xt is set.

Further, the i-th component ext (i) of the array ext is set with the extension character K of the element of the dictionary indicated by the reference number i, and the i-th component next (i) of the array next is set. Is
A pointer indicating an element in the horizontal hierarchy (see FIG. 15) of the element with the reference number i is set.

Note that the dictionary search arrays are first array
It is represented by [1, NMAX], next [1, NMAX], ext [1, NMAX]. Next, the first character K is read, the reference number corresponding to this character K is set in the variable i, and the encoding process is started.

First, as the maximum use address A of the dictionary,
The maximum used address of the currently registered character string is set (n → A) (S2). Next, with the extended character set to K, a character of the input character string is read (S3), and if there is a character to be read next (S4), a dictionary search process is performed.

In this case, the variable i is set to another variable ω (reference number) (i → ω), and the variable j is set to the initial value 0 (0 →
j) Yes (S5). Next, the dictionary search process (S9, S1
0, S6, S11, S12) is performed, but in this dictionary search processing, first, the number of the component of the array next indicated by the value of the component first (i) corresponding to the variable i is set in the variable i {ext ( i)
→ symbol; first (i) → i} (S9).

After that, when it is determined that i = 0 is not satisfied (S10), the elements stored in the corresponding list are used as the candidate elements, and the dictionary search processing in this list is performed.
In this process, first, it is determined whether i ≦ A (S6),
If i ≦ A, the component ext (i) indicating the extended character of the corresponding candidate element is compared with the extended character K (S12), and if they are not equal, the next set to the component next (i) is set. Of the candidate element of {i → j; ext (i) as a new variable i
→ symbol; next (i) → i} (S11), and the process returns to S10.

If i> A in the process of S6, an error (S8) is determined and the dictionary search process is stopped. In this way, the processes of S10 to S12 are repeated to search the corresponding list.

Further, in the processing S12, the component ext
When (i) = symbol = K, it is determined that the partial string that matches the input character string is registered in the dictionary, the process returns to step S3, the next character is read, and this character is Encode the added character string.

On the other hand, when the value of the component first (i) or next (i) corresponding to the variable i is 0, i = 0 (S10). In this case, it is determined that no other candidate element linked to the substring with the reference number i is registered in the dictionary, and the following processing is performed.

Here, as described above, every time the corresponding partial string is searched from the dictionary, the reference number corresponding to the searched partial string is saved in the variable ω in step S5. Therefore, the reference number saved in this variable ω indicates the registered substring that has the longest match with the input character string, and the code {code (ω)} corresponding to this reference number ω is output (S13). ).

Then, a new subsequence registration process (S14)
~ S19) is performed. In this registration process, first, the value of the variable n is set to the variable i (n → i), and the variable n is incremented (n + 1 → n) (S14).

The value of the maximum used address A is also incremented (n + 1 → A) (S15). Next, it is judged whether or not the variable j is j = 0 (S16), and if j = 0, fi
The variable i is set in rst (ω) {i → first (ω)}, and ex
Set the extended character K to t (ω) {K → ext (ω)} (S
17), define a list corresponding to the reference number ω.

On the other hand, if j = 0 is not satisfied (S16), next
The variable i is set in (ω) {i → next (ω)}, and ext
The extended character K is set in (ω) {K → ext (ω)} (S
19). In this way, after the registration process is completed, the reference number corresponding to the extended character K is set as the variable i (K → i) (S18), the process returns to the process S3, and the above process is repeated.

After that, when there are no more characters to be read (S4), the code {code corresponding to the variable ω at that time is {code
(Ω)} is output and the process ends. (3) Description of processing at the time of data restoration ... See FIGS. 5 and 6. At the time of data restoration, the input data (encoded data) is decoded by the external hash method and the restored data is output. In this case, Also, in order to monitor whether or not erroneous data has been used during the process, the search address and the maximum used address are compared at the time of dictionary search.

The processing at the time of data restoration will be described below with reference to the processing flowcharts of FIGS. The process numbers in the figure are shown in parentheses. Data (encoded data)
In the decompression process, the character string consisting of one character for all characters is registered in the dictionary in advance as an initial value, and then decoding is started, as in the case of encoding.

Initialization (S21) is performed first, and this processing is the same as the processing (S1) in FIG. Next, n is set to the maximum use address A (n → A) (S22).

Then, the first code (reference number) is read, and the current code (code) is old code (OLDcode).
), The code of the character K that matches the input code is searched, and the character K is output (S23).

The output character K is set (K → FINchar) in "FINchar" for post-processing.
After that, read the next code input code (CODE → IN code)
(S24), it is checked whether or not there is a new code, that is, whether or not code input is completed (S25), and the process proceeds to the next process.

Next, if there is a new code, it is checked whether or not the input code code is defined (registered) in the dictionary (S26). If not, "FINchar
The character K of "is temporarily stacked (FINchar → stack
), And the reference number code as a new code (OLDcode
→ code) (S29).

However, if the input code code is defined in the dictionary (S26), it is determined whether the address of the code code (CODE) is the minimum address (NMIN) or more (CODE ≧ NM).
IN) is judged (S28), and if it is the minimum address or more, whether the code code is the maximum use address A or less (CO
DE ≦ A) is determined (S27).

In this judgment, if it is larger than the maximum used address (CODE> A), it is judged as an error (S30) and the processing is stopped. However, the maximum used address or less (CODE ≤
In the case of A), since the process is normal, the following process is performed. That is, until the code code (CODE) becomes the minimum value NMIN (minimum value of address) of the currently registered character string n (S2
8) Read the data at the next address from the before code in the dictionary {ext (CODE) → stack; before (CODE) → COD
E} (S31).

When the code code (CODE) becomes smaller than the minimum value NMIN (minimum value of address) of the currently registered character string n (CODE <NMIN) (S28), the character K is output {K → FI.
Nchar}, and dictionary registration processing is performed (S32).

The dictionary registration processing is performed in the same manner as the processing (S7) of the conventional example shown in FIG. At this time, "OLDcod
e → before (n) ”and“ K → ext (n) ”. Then, the maximum use address A is incremented (n + 1 → A) (S33), and n is further incremented (n + 1 → n).
Then, the code is updated (INcode → OLDcode) (S3)
4).

When the above process (S34) is completed, S23
Then, the process returns to and the above process is repeated. (Explanation of Second Embodiment) FIG. 7 is a diagram showing a data compression / decompression device according to a second embodiment of the present invention. In the figure, 10 is a data compression / decompression device, 11 is a DMA control circuit, and 12 is. MP
U (microprocessor), 13 is a dictionary search circuit, 14
Is an input / output port, 15 is an address determination unit, 16 is an address holding unit, 17 is a pipeline control circuit, 18 is a continuous address circuit, 19 is a continuous detection circuit, 20 is a match check circuit, 3A is a dictionary memory, and 21 is a plurality. The character reading circuit is shown.

(1) Description of data compression / decompression device--see FIG. 7 In the second embodiment, data compression / decompression processing is performed by the device shown in FIG.

As shown in FIG. 7, the data compression / decompression device 10 is provided with a DMA control circuit 11, an MPU 12, a dictionary memory 3A, a dictionary search circuit 13, and an input / output port 14. Further, the dictionary search circuit 13 includes the address determination unit 1
5, address holding unit 16, pipeline control circuit 17,
A continuous address circuit 18, a continuous detection circuit 19, a match check circuit 20, and a plural character reading circuit 21 are provided.

(2) Description of Operation The data compression / decompression process in the data compression / decompression device shown in FIG. 7 will be described below.

Original data (character data or code word data) to be processed is DMA (Direct Memory Access)
It is input via the control circuit 11. M as a control procedure
The PU 12 sets the input original data to one character and the reference number of the character string so far in the plural character reading circuit 21 of the dictionary searching circuit 13, and then activates the dictionary searching circuit 13.

After that, the dictionary search circuit 13 uses the dictionary memory 3A.
The candidate character of the character string further extended by one character is read, the match checking circuit 20 checks the match between the input character and the candidate character, and the continuous detection circuit 19 detects the presence or absence of the candidate character.

Here, the maximum address registered in the dictionary is always stored in the address holding unit 16, and the dictionary memory 3A is compared with the address for reading the dictionary memory for searching. If the search is larger than the registered address, it is regarded as an invalid search and the processing is interrupted.

The pipeline control circuit 17 reads the next candidate character into the dictionary memory 3A in parallel with the matching check circuit 20 collating the input character and the candidate character and the continuous detection circuit 19 checking the input character and the presence / absence of the candidate character. multiply.

As described above, the pipeline control circuit 17 performs the pipeline processing, so that the search and collation processing for each of a plurality of candidate characters can be executed in the cycle time of the dictionary memory 3A.

Further, the dictionary search circuit 13 is provided with a continuous address circuit 18 for generating a continuous address and reading the hash address and the candidate character registered in the continuous address of the dictionary memory 3A in the plural character reading circuit 21. ..

In encoding the LZW code, the dictionary memory 3A is used.
Find the character string that matches the maximum length in. Therefore, it is understood that the input character is added and the character string is sequentially extended one character at a time, and when there are no candidate characters, the character string has the maximum matching length.

At this time, up to the maximum matching length character string is represented by reference numbers using the address ω.
Outputs the reference number ω from the input / output port 14 to the outside as a compressed code. Also, the set of the reference number ω and the last input character is registered in the dictionary. At this time, the target address of the dictionary is written in the address holding unit 16.

On the other hand, to restore the LZW code, the dictionary memory 3A is accessed by the input code to restore the characters one by one while following the linked list, and when the reference number becomes 0, a plurality of characters that have already been restored are restored. Output the column as character string data. Similar to the compression, the processing is performed while comparing the search addresses to confirm that they have been registered in the dictionary.

[0138]

As described above, the present invention has the following effects. (1) During data compression processing and data decompression processing,
Destruction of the address pointer of the dictionary can be determined by holding the maximum address of the currently registered dictionary and confirming that the address of the dictionary used for the search is in use.

(2) It is possible to detect an error in the transmitted or accumulated reference number (codeword) by determining whether or not the reference number (codeword) to be restored is registered at the time of data restoration. As a result, it is possible to determine the invalidity of the encoding operation during the processing, and it is possible to realize a highly reliable compression / decompression device.

[Brief description of drawings]

FIG. 1 is a principle diagram of the present invention.

FIG. 2 is a diagram showing a data compression / decompression device according to the first embodiment of the present invention.

FIG. 3 is a data compression processing flowchart (part 1) of the first embodiment.

FIG. 4 is a data compression processing flowchart (part 2) of the first embodiment.

FIG. 5 is a flowchart (part 1) of a data restoration process of the first embodiment.

FIG. 6 is a data restoration process flowchart (No. 2) of the first embodiment.

FIG. 7 is a data compression / decompression device of a second embodiment.

FIG. 8 is a diagram showing a conventional data compression / decompression device.

FIG. 9 is a flowchart of a conventional LZW encoding process.

FIG. 10 is a flowchart of a conventional LZW decoding process.

11A is an explanatory view of a concrete example of conventional LZW encoding, and B.
FIG. 6 is an explanatory diagram of a dictionary configuration example.

FIG. 12 is a diagram illustrating a specific example of conventional LZW decoding.

FIG. 13 is an explanatory diagram of a list structure of an external hash method.

FIG. 14 is a configuration example of a dictionary memory (at the time of encoding).

FIG. 15 is an explanatory diagram of a dictionary (at the time of encoding).

FIG. 16 is a flowchart of a conventional LZW encoding process by the external hash method.

FIG. 17 is a configuration example of a dictionary memory.

FIG. 18 is an explanatory diagram of a dictionary (at the time of restoration).

FIG. 19 is a flowchart of a conventional LZW decoding process by the external hash method.

[Explanation of symbols]

 1 data compression device 2 compression unit (data compression unit) 3 dictionary unit 4 data decompression device 5 decompression unit (data decompression unit) 6 comparison unit 7 maximum use address holding unit

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Shigeru Yoshida 1015 Kamiodanaka, Nakahara-ku, Kawasaki-shi, Kanagawa Fujitsu Limited

Claims (8)

[Claims] 1. A data compression unit (2) and a dictionary unit (3)
In the dictionary unit (3), the encoded data is divided into different subsequences, a different reference number (ω) is added to each subsequence and registered, and the compression unit (2 ), The external hash method is used to search the dictionary part (3), and the input data is coded by designating it with the reference number (ω) of the substring that matches the maximum length of the substring registered in the dictionary part (3). In the data compression method for digitizing, the subsequence stores information holding means for holding information indicating an area registered in the dictionary unit (3), and the information holding unit when searching the dictionary unit (3). A determination unit that determines whether or not the registered region that has been registered is searched, and if the determination unit determines that a region other than the registered region is being searched for, then an error is detected. A data compression method characterized by: 2. The data compression method according to claim 1, wherein the information holding means is a maximum used address holding unit (7) which holds a maximum address value registered in the dictionary unit (3). 3. The comparing unit (6) for comparing the address value used in the search of the dictionary unit (3) with the address value held in the maximum used address holding unit (7). The data compression method according to claim 2, wherein 4. When the address value used in the search of the dictionary part (3) is larger than the address value held in the maximum used address holding part (7) by the comparison of the comparison part (6), it is invalid. 4. The data compression method according to claim 3, wherein the processing is interrupted as the retrieval. 5. A data restoration unit (5) and a dictionary unit (3)
In the dictionary unit (3), the encoded data is divided into different subsequences, and a different reference number (ω) is added to each subsequence and registered. ), In the substring registered in the dictionary unit (3)
By inputting a code word which is designated by the reference number (ω) and has a maximum length matching as input data and searching the dictionary unit (3) using the external hash method based on the input data, In a data restoration method for restoring data of an original substring, the substring stores information holding information indicating an area registered in the dictionary section (3), and when searching the dictionary section (3), A determination means is provided for determining whether or not the registered area held in the information holding means is searched, and when the determination by the determination means searches for areas other than the registered area, A data restoration method characterized by being detected as an error. 6. The data restoration method according to claim 5, wherein said information holding means is a maximum used address holding unit (7) which holds the maximum address value registered in the dictionary unit (3). 7. The comparing unit (6) for comparing the address value used in the search of the dictionary unit (3) with the address value held in the maximum used address holding unit (7). 7. The data restoration method according to claim 6, wherein 8. If the address value used in the search of the dictionary section (3) is larger than the address value held in the maximum used address holding section (7) by the comparison of the comparison section (6), it is invalid. 8. The data restoration method according to claim 7, wherein the processing is interrupted as a special search.