JP2009246973A - Decoding accelerating apparatus for variable length code - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a decoding accelerating apparatus for a variable length code, in which a decoding speed of an entire variable length code decoder can be accelerated while using a decoding method for differentiating decoding of a long codeword and decoding of a short codeword. <P>SOLUTION: A decoding accelerating apparatus includes: a codeword identification unit configured to determine in an input code segment is a short codeword; and a short codeword decoding accelerating unit configured to calculate code segment request information for immediately requesting the next input code segment so as to request the next input code segment by acquiring the code segment request information before perfectly decoding the decoding processing waiting codeword, when it is decided that the decoding processing waiting codeword is the short codeword by the codeword identification unit. The decoding accelerating apparatus for a variable length code is applied to e.g., a variable length code decoder and by accelerating decoding of a short codeword which may occur highly frequently, a decoding speed of the entire variable length code decoder can be accelerated. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to variable-length code decoding, and more specifically, to a variable-length code decoding speed-up device, and a variable-length code decoding device and method using the variable-length code decoding speed-up device.

  Variable length code decoders are a very important part in video decoders. The decoder encodes using code words having different lengths depending on the frequency with which symbols occur in the bitstream, encodes frequently occurring symbols with short code words, and encodes less frequently occurring symbols with long code words. Encode. Since the length of the codeword is variable, the interdependency is high in the entire decoding process, and it is difficult to increase the decoding speed by the parallel processing method. The most widely used variable-length code decoding method at present is the lookup table method (LUT method). In such a method, a code segment having a fixed number of bits is read from a bit stream, and a code table is searched as an index. In order to reduce the size of the code table and improve the search speed of the code table, an optimization method such as a multi-step LUT method has been proposed. As these optimization methods, for example, a variable length code decoding method using the LUT method of two stages or two or more stages disclosed in Patent Document 1, or simply a high-speed LUT method disclosed in Patent Document 2 is used. There is a decoding method of MPEG video data for determining DCT coefficients which are main data in an MPEG-2 video stream. The entire disclosure of these related patents is incorporated by reference.

  Usually, as described above, the variable-length code decoding method using the conventional LUT method mainly includes three stages. (1) Codeword request stage: The decoder outputs code segment request information for requesting the next input code segment in this stage. For example, the decoder outputs the number of barrel shifter shift bits to the barrel shifter for the MPEG-2 / 4 / VC-1 standard, or the exponent Golomb code order for the exponent Golomb code for the AVS standard. The next input code segment is requested by outputting to the generator. (2) Code segment acquisition stage: A unit that generates the next input code segment, such as a barrel shifter / exponential Golomb code decoder, for example, at this stage, the number of shift bits of the barrel shifter / the order of the exponent Golomb code, etc. Based on, the next input code segment is generated and provided to the decoder. (3) Codeword decoding stage: In this stage, the input code segment is indexed, and the encoded symbol and the next codeword are decoded from the code table (ie, the next input code segment is requested). ) (For example, the number of shift bits of the barrel shifter or the order of the exponent Golomb code). The above three steps are executed in order. As shown in Fig. 5, the code word request stage and the code segment acquisition stage occupy one clock cycle each, while the code table in the video standard is large in size and generally has SRAM (Static Random Access). Since the code table search, that is, the codeword decoding stage generally requires two clock cycles, the time for accessing the memory is in the codeword request stage and the code segment acquisition stage. It is very long compared to the time required. For this reason, the speed of variable-length code decoding is mainly determined by the time for searching the code table. For long codewords, enough time is decoded to allow enough time to access the memory, but for short codewords, too slow decoding speeds degrade overall decoder performance. .

U.S. Pat.No. 5,253,053 U.S. Patent No. 6,011,498

  An object of the present invention is to differentiate between decoding of long codewords and decoding of short codewords in order to solve the problem that the decoding speed of the above short codewords affects the performance of the entire decoder. An object of the present invention is to provide a variable speed code decoding speed-up device that can improve the decoding speed of the entire variable length code decoder by using a decoding method.

  According to one aspect of the present invention, a codeword identification unit configured to determine whether a codeword waiting for decoding in an input code segment is a short codeword, and waiting for decoding processing by the codeword identification unit. When it is determined that the code word is a short code word, the next input code is immediately acquired so that the code segment request information is obtained and the next input code segment is requested until the decoding of the code word waiting for decoding is completed. A variable-length code decoding speed-up device comprising a short codeword decoding speed-up unit configured to calculate code segment request information for requesting a segment.

  According to the present invention, the short codeword is preferably a codeword having a length of N bits or less, where N is the average time required to decode the codeword when the short codeword is not optimized. It is a positive integer preset based on a desired decoding speed.

  According to the present invention, the decoding-waiting codeword is preferably a codeword encoded according to the MPEG-2, MPEG-4, or VC-1 standard. In this case, the code segment request information is the number of shift bits for acquiring the next input code segment. The codeword identification unit determines whether the codeword waiting for decoding in the input code segment is a short codeword by checking the higher-order bits in the input code segment based on the encoding method of the variable length code. The short codeword decoding acceleration unit is configured to output the number of shift bits corresponding to the decoding process waiting codeword determined to be a short codeword based on the variable length code encoding method.

  According to the present invention, the decoding process waiting codeword is preferably a codeword encoded in accordance with the AVS standard. In this case, the code segment request information is the order of an exponential Golomb code for obtaining the next input code segment. The codeword identification unit compares the value of the input code segment with a predetermined threshold value, and when the value of the input code segment is equal to or less than the predetermined threshold value, the codeword waiting for decoding in the input code segment is a short codeword Judge. The short codeword is a codeword having a length of N bits or less, and the predetermined threshold is preferably a maximum value that can be displayed by an N-bit exponential Golomb code. Further, the short codeword decoding acceleration unit obtains the order of the exponent Golomb code corresponding to the value of the input code segment based on the variable-length code encoding method when the decoding-waiting codeword is a short codeword. Is configured to do.

  Therefore, the variable-length code decoding speed-up device according to the present invention is applied to, for example, a variable-length code decoding device, and by speeding up decoding of frequently occurring short code words, the variable-length code decoding device The overall decoding speed can be improved.

It is a figure which shows the variable-length code decoding process by this invention. 1 is a diagram illustrating a variable-length code decoding apparatus that can be used for decoding a bitstream based on the MPEG-2 / 4 / VC-1 standard according to an embodiment of the present invention. FIG. FIG. 10 is a diagram illustrating a variable-length code decoding apparatus that can be used for decoding an AVS standard bitstream according to another embodiment of the present invention. FIG. 5 is a diagram illustrating a variable-length code decoding apparatus that can be used for decoding an AVS standard bitstream according to another embodiment of the present invention. It is a figure which shows the variable-length code decoding process in a prior art.

  Hereinafter, in order to understand the present invention more fully, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. In all the drawings, the same reference numerals denote the same or similar members.

  A specific embodiment of the variable-length code decoding apparatus according to the present invention will be described below with reference to FIGS. Note that the present invention is described with respect to the MPEG-2 / 4 / VC-1 standard and the AVS standard that are commonly used in video compression encoding / decoding, but such description is merely for explanation and applied to the present invention. It should be apparent to those skilled in the art that the compression encoding / decoding standard to be performed is not limited to this, and may be, for example, the JPEG standard, the CCITT standard, or any other variable length encoding / decoding standard. is there.

  FIG. 1 shows a variable length code decoding process according to the present invention. In the upper part, the decoding process when a codeword waiting for decoding in an input code segment is a short codeword is shown. The decoding process when the decoding process waiting codeword is a long codeword is shown.

  Prior to the description of FIG. 1, the terms input code segment and decoding process waiting codeword described in the present invention will be briefly described. In the usual case, the variable-length bit stream can be divided into fixed-length code segments one by one, and these code segments are continuously input to the decoder and decoded. Each fixed-length code segment includes one or more variable-length encoded codewords encoded by the variable-length encoding method. When the decoder decodes one code segment, only one input encoded codeword from the top of the input code segment is decoded, and the remaining undecoded bits in the input code segment are decoded Decoded when the decoder decodes subsequent input code segments. For this reason, in the present invention, these fixed-length code segments are referred to as input code segments, and one encoded codeword that is actually decoded and has a variable length from the top of the input code segment is assigned to the input code segment. This is called a decoding process waiting codeword.

  As shown in FIG. 1, when calculating code segment request information for requesting the next input code segment in order to speed up the decoding of the variable-length code, the decoding process waiting codeword is a short code. A different calculation method is adopted for an input code segment that is a word and an input code segment whose decoding process waiting codeword is a long codeword. When the decoding process waiting code word is a short code word, after obtaining the current input code segment, the decoding process waiting code word in the input code segment is decoded, and the next input code segment is set by a dedicated circuit. Code segment request information for requesting can be calculated, and it is not necessary to obtain the code segment request information from the code table memory. You can get and request the next code segment. For this reason, the step of requesting the next code segment does not start after the decoding of the codeword waiting for decoding is completed, but is performed in parallel with the codeword decoding step. The decoding speed is increased. In the case where the decoding process waiting code word is a long code word, the code segment request information for requesting the next input code segment is acquired in the decoding stage, and after the decoding is completed, the next code Begin requesting a segment. According to the present invention, since the decoding speed of frequently occurring short codewords is greatly improved, the variable-length code decoding process is accelerated overall. Here, the illustration of FIG. 1 simply shows the relative relationship between the execution times of the respective operation stages in the normal decoding process, and this illustration shows the execution time of each operation stage of the present invention. It should not be regarded as a limitation, and the decoding process only needs to conform to the gist of the present invention.

  Based on FIG. 2, a variable-length code decoding apparatus and its decoding process for an MPEG-2 / 4 / VC-1 standard bitstream according to an embodiment of the present invention will be described. FIG. 2 shows a variable-length code decoding apparatus 201 used for decoding an MPEG-2 / 4 / VC-1 video stream according to this embodiment. The variable length code decoding apparatus 201 receives an input code segment (InCodSeg) 202 having a fixed length output from the barrel shifter 212 as an input. The decoding process waiting codeword in the input code segment 202 is decoded by the variable-length code decoding apparatus 201 to generate a decoded codeword (DecCode) 213. The variable length code decoding apparatus shown in FIG. 2 employs a decoding process as shown in FIG. In order to realize the decoding process, the code segment request information for requesting the next input code segment is stored in the code table memory in the decoding unit 208 when the decoding process waiting codeword is a short codeword. Without being accessed, the short codeword decoding speed-up unit 207 obtains it by calculation. Hereinafter, a specific operation in the decoding process of each functional unit in FIG. 2 will be described in detail.

  In the variable-length code decoding apparatus 201, when the input code segment 202 is obtained from the barrel shifter 212, the input code segment 202 is input to the decoding unit 208 and decoded, and the input code segment 202 is input to the codeword identification unit 203. Is also entered. In the codeword identification unit 203, the codeword waiting for decoding in the input code segment 202 is a long codeword (the codeword length is longer than N) or a short codeword (the codeword length is N or less). Determine if there is. When it is determined that the codeword waiting for decoding in the input code segment 202 is a short codeword, the codeword identification unit 203 converts the input code segment 202 via the short codeword information (SCode) 205 to the input code segment Input to the 202 short codeword decoding acceleration unit 207.

  Here, the value N is an average time (number of clock cycles) required to decode one codeword in a normal case (when decoding of a short codeword is not accelerated) and a desired decoding speed (bit / bit). Based on the clock cycle). For example, if a decoding speed of at least 1 bit / clock cycle is required but 5 clock cycles are required to decode one codeword, the length is 5 unless the decoding of the short codeword is optimized. Since the decoding speed of codewords less than 1 bit is lower than 1 bit / clock cycle, it is possible to optimize codewords with a length of 5 bits or less (ie, N = 4) as short codewords. . The setting relating to the value N here also applies to other embodiments.

ただし、「ｘ」は、当該ビットが「0」又は「1」であることを表す。 According to the decoding method defined in the MPEG-2 / 4 / VC-1 standard, the codeword identification unit 203 uses the following matching mechanism to determine whether the codeword waiting for decoding in the input code segment is a short codeword Can be judged. For example, when N = 4, the input code segment from the top of the input code segment is compared with a codeword whose length specified by the encoding method is 4 bits or less, and the codeword waiting for decoding processing in the input code segment Is a short code word. For example, in the MPEG-2 standard, the short codeword determination rule can be set as follows based on the setting in the MPEG-2 standard. When the decoding code table is DCT coefficient table 0, the short codeword determination rules are those shown in Table 1, and when the decoding code table is DCT coefficient table 1, the short codeword determination rules are Table 2. Is shown in 1. Any of the tables described herein is intended to represent a mapping mechanism, not a map table that is actually stored.

However, “x” represents that the bit is “0” or “1”.

  When the decoding code table is the DCT coefficient table 0, as shown in Table 1, if the most significant 2 bits of the input code segment is 10 or 11, the code word waiting for decoding processing is 10 according to the MPEG-2 standard. Or 11 because the length is 2 bits, it is determined that the decoding process waiting codeword is a short codeword, and if the most significant 3 bits of the input code segment is 011, the decoding processing waiting codeword Since the word is 011 and its length is 3 bits, it is determined that the decoding-waiting codeword is a short codeword, and if the most significant 4 bits of the input code segment are 0100 or 0101, decoding is performed. The code word waiting for processing is 0100 or 0101 and its length is 4 bits. Therefore, the code word waiting for decoding is determined to be a short code word. If the input code segment is in any other case, the length of the codeword that is actually decoded at this time is longer than 4 bits according to the MPEG-2 standard. Is determined to be a long codeword.

  As described above, the codeword identification unit 203 determines whether the decoding process waiting codeword in the input code segment is a short codeword by the variable length code encoding scheme, specifically, the type of the current decoding code table, and It is possible to determine whether the codeword waiting for decoding in the input code segment 202 is a short codeword of N bits or less from at most N bits from the most significant bit of the input code segment 202. For example, a person skilled in the art can design a logic circuit with the codeword identification unit 203 to compare an input code segment from the top of the input code segment 202 with a codeword of N bits or less defined in the current decoding code table. When matching with a certain short code word in the decoding code table appears, the determination process can be immediately terminated. For this reason, the maximum number of bits in the input code segment actually compared here is 4 bits from the most significant.

  The judgment rules shown in Table 1 and Table 2 are exemplary when the codec standard is the MPEG-2 standard, and those skilled in the art are prescribed by other standards such as MPEG-4 / VC-1 etc. It should be possible to easily set a similar short codeword decision rule that adapts to these standards, depending on the coding scheme being used.

  According to the above determination rule, there are two outputs of the codeword identification unit 203: a mode signal (Mode) 204 and a short codeword signal (SCode) 205. The mode signal 204 indicates whether the decoding process waiting codeword in the input code segment 202 is a short codeword (for example, mode signal = “0”) or a long codeword (for example, mode signal = “1”). When the mode signal indicates that the code word waiting for decoding in the input code segment 202 is a short code word, the code word identification unit 203 decodes the input code segment 202 via the short code word information 205. Input to the acceleration unit 207.

  As described above, a code segment request for requesting the next input code segment for an input code segment whose decoding process waiting codeword is a long codeword and an input code segment whose decoding process waiting codeword is a short codeword The calculation of information is realized in different units. In this embodiment, the code segment request information is the number of shift bits of the barrel shifter 212. Specifically, for the input code segment 202 in which it is determined that the decoding process waiting codeword is a short codeword, the short codeword decoding acceleration unit 207 calculates the short codeword shift bit number (SCodeSBitNum ) 209 is calculated and output, whereas for the input code segment 202 in which the decoding process waiting codeword is determined to be a long codeword, the decoding unit 208 performs code table memory based on the input code segment 202. To obtain and output the long codeword shift bit number (LCodeSBitNum) 210.

Next, a process in which the short codeword decoding acceleration unit 207 calculates the number of shift bits will be described. The number of shift bits is the length of a decoding process waiting codeword in the current input code segment. In this embodiment, the length of the decoding process waiting codeword in the current input code segment is calculated by using the mapping mechanism, that is, the type of the current decoding code table and at most N from the top of the input code segment. The length of the codeword waiting for decoding in the input code segment can be calculated from the bits. For example, in the MPEG-2 standard, when the current decoding code table is DCT coefficient table 0, the mapping mechanism for calculating the number of short codeword shift bits is shown in Table 3, but the current decoding code table is DCT coefficient table 0. In the case of the coefficient table 1, the mapping mechanism for calculating the number of short codeword shift bits is shown in Table 4. In addition, in the case of other decoding standards, it is obvious to those skilled in the art that the short codeword shift bit number 209 can be calculated by setting a similar mapping mechanism depending on the encoding method defined in these standards. Should be.

  As described above, the operations of the codeword identification unit 203 and the short codeword decoding acceleration unit 207 are all related to the type of the current decoding code table, but for the MPEG-2 / 4 standard, The type of is determined by other modules in the video decoder and does not always change with respect to the variable length code decoder and corresponds to a fixed parameter, so in the actual implementation, the codeword identification unit 203 and the short codeword decoding acceleration unit 207 receive the current decoding code table type information (not shown) from the outside, and select and use an appropriate mapping relationship based on the information according to the above-described method. Good.

  Hereinafter, a decoding process performed by the decoding unit 208 according to the present embodiment will be described. In the codeword decoding stage, the decoding unit 208 uses the input code segment 202 as an index, and checks the variable length code table in the code table memory by decoding a decoded codeword (DecCode) (run length / coefficient value) 213. And a long codeword shift bit number 210 for requesting the next input code segment. Since the decoding unit 208 can use a general-purpose decoding unit in the prior art, the variable-length code decoding speed-up device of the present invention can be easily applied to the conventional variable-length code decoding device. is there.

表中の「x」は当該ビットが「0」または「1」が可能であることを表す。 For example, with respect to DCT coefficient table 0 based on MPEG-2, the mapping table for decoding and generating the number of shift bits stored in the code table memory is as shown in Table 5.

“X” in the table indicates that the bit can be “0” or “1”.

  The information for requesting the next input code segment output by the decoding unit 208 is simply called the long codeword shift bit number 210, but the decoding unit 208 according to this embodiment is a general-purpose decoding in the prior art. Therefore, the decoding unit 208 always outputs the number of shift bits after decoding is completed, regardless of whether the codeword waiting for decoding in the input code segment is a long codeword or a short codeword. Accordingly, the long codeword shift bit number 210 output from the decoding unit 208 actually includes the short codeword shift bit number. However, due to the presence of the selector 214, the number of short codeword shift bits output from the decoding unit 208 is not output to the barrel shifter 211. That is, the number of short codeword shift bits is only intermediate output information, and is not used for actual operation. It should be understood by those skilled in the art that it does not work.

  The mode information 204 output from the codeword identification unit 203 is input to the selector 214, and the selector 214 is controlled so that the short codeword shift bit number 209 or the long codeword shift bit number 214 is output to the barrel shifter 212. To do. For example, if the mode information 204 = “0”, the short codeword shift bit number 209 is output as the shift bit number (SbitNum) 211 via the selector 214 to request the next input code segment. Otherwise, if the mode information 204 = “1”, the long codeword shift bit number 210 is output as the shift bit number 211 via the selector 214 to request the next input code segment.

  Next, a variable-length code decoding apparatus 301 for an AVS standard bitstream and its decoding process according to another embodiment of the present invention will be described with reference to FIG. FIG. 3 shows a variable-length code decoding apparatus 301 for decoding an AVS standard bitstream. The input of the variable length code decoding device 301 is an input code segment (InCodSeg) 302 having a fixed number of bits output from the exponent Golomb code decoder 311. The decoding process waiting codeword in the input code segment 302 is decoded by the variable-length code decoding apparatus 301 to generate a decoded codeword (DecCode) 312. The variable length code decoding apparatus 301 also employs the decoding process shown in FIG. In order to realize the decoding process, the code segment request information for requesting the next input code segment (in this embodiment, the order of the exponent Golomb code) is not obtained after the decoding is completed. Rather, it is calculated by the short codeword decoding acceleration unit 306.

  In the variable-length code decoding apparatus 301, after acquiring the input code segment 302 from the exponent Golomb code decoder 311, the input code segment 302 is input to the decoding unit 307 to decode the codeword waiting for the decoding process. At the same time, it is also input to the codeword identification unit 303. In the codeword identification unit 303, whether the codeword waiting for decoding in the input code segment 302 is a long codeword (a bit longer than N) or a short codeword (a bit whose length is N or less) Judging. When the codeword identification unit 303 determines that the decoding process waiting codeword in the input code segment 302 is a short codeword, the codeword identification unit 303 converts the input code segment 302 into the short code via the short codeword information (SCode) 305. Input to the word decoding speed-up unit 306.

The codeword identification unit 303 can determine whether the codeword waiting for decoding in the input code segment 302 is a short codeword by comparing the value of the input code segment with a predetermined threshold. Here, the input code segment is a fixed-length binary bit stream output from the exponential Golomb code decoder, and the value is a decimal number displayed by the bit stream. To be determined. When the value of the input code segment is equal to or smaller than the predetermined threshold, it is determined that the decoding process waiting codeword in the input code segment is a short codeword, and conversely, when the value of the input code segment is larger than the predetermined threshold The decoding process waiting codeword in the input code segment is determined to be a long codeword. For example, when N = 4, the maximum number of 4-bit exponential Golomb codes that can be displayed is 7. Therefore, the threshold value can be set to 7. Accordingly, the determination rule is as shown in Table 6. If the value of the input code segment is 7 or less, the codeword waiting for decoding in the input code segment is determined to be a short codeword. Conversely, if the value of the input code segment is greater than 7, decoding in the input code segment is performed. The codeword waiting for conversion processing is determined to be a long codeword.

  According to the coding scheme of the exponent Golomb code, when the value of the input code segment <= 7, the decoding process waiting codeword in the input code segment may actually be a codeword larger than 4 bits. However, there are few cases in this case. Even if some codewords larger than 4 bits are determined to be short codewords and optimized, the effect of this embodiment is not affected. This is because the present invention only needs to ensure the decoding of a codeword having a length of 4 bits or less.

  The codeword identification unit 303 has two outputs, a mode signal (Mode) 304 and a short codeword signal (SCode) 305. The mode signal 304 indicates whether the codeword waiting for decoding in the input code segment 302 is a short codeword (for example, mode signal = “0”) or a long codeword (for example, mode signal = “1”). When the mode signal indicates that the codeword waiting for decoding in the input code segment 302 is a short codeword, the codeword identification unit 303 decodes the input code segment 302 via the shortcodeword information 305. Input to the acceleration unit 306.

  The short codeword decoding acceleration unit 306 calculates an exponent Golomb code order (SCodeExpOrder) 308 of the short codeword based on the value of the input code segment 302 input via the short codeword information 305.

  In the AVS standard, the order of the exponent Golomb code is determined by a decoding code table. Before describing specific operation processing of the short codeword decoding acceleration unit 306, the principle of determining the degree of the exponential Golomb code of a short codeword according to the AVS standard will be briefly described.

Correspondences shown in Tables 7 to 9 are obtained by the encoding method defined in the AVS standard. Among them, the following code table can be found from the value of the code segment and the current code table.

The order of the exponent Golomb code corresponds to the code table used by the decoding method of the AVS standard. For this reason, the mapping relationships shown in Table 10 to Table 12 are obtained. Among them, the order of the exponent Golomb code can be determined from the value of the code segment and the current code table.

  Using the above characteristics of the AVS standard, the short codeword decoding speed-up unit 306 of this embodiment can determine the order of the exponent Golomb code of the codeword waiting for decoding processing from the values of the current code table and the code segment. . Hereinafter, the operation performed in the short codeword decoding acceleration unit 306 according to the present embodiment will be described in detail.

  When the codeword identification unit 303 determines that the codeword waiting for decoding in the input code segment 302 is a short codeword, the input code segment 302 is input to the short codeword decoding acceleration unit 306 via the short codeword information 305. . Thereafter, the short codeword decoding speed-up unit 306 calculates information for requesting the next input code segment, that is, the degree 308 of the exponential Golomb code of the short codeword from the mapping relationships shown in Tables 10 to 12.

  Further, the short codeword decoding acceleration unit 306 further determines the type of the next code table from the mapping relationships shown in Tables 7 to 9, and operates in the case where the next decoding process waiting codeword is a short codeword. The type of the next determined code table is stored for use. That is, if the codeword immediately preceding the decoding process is a short codeword, the short codeword decoding speed-up unit 306 uses the previously determined code table type stored in the codeword index of the current decoding process waiting codeword. The order of the Golomb code and the type of the next code table are determined. On the other hand, when the codeword immediately preceding the decoding process is a long codeword, the short codeword decoding acceleration unit 306 selects the code table selection / decoding unit in the decoding unit 307 via the code table type identification signal (CodTabIdf) 315. Using the type of code table received from exponent Golomb code order generation unit 313, the order of the exponent Golomb code of the current decoding process waiting codeword and the type of the next code table are determined. For example, those skilled in the art can easily understand that the mode signal 304 can control the short codeword decoding acceleration unit 306 to select and use an appropriate code table type indicator.

  The mapping relationships shown in Tables 7 to 9 and Tables 10 to 12 may be stored or programmed in the short codeword decoding acceleration unit 306, or may be stored in another storage device. For example, when the codeword waiting for decoding is a short codeword, a module for determining the type of the next code table is provided separately from the short codeword decoding acceleration unit 306, and the code determined by the module is determined. The type of the table may be input to the short codeword decoding speed-up unit 306 and used for the operation when the next decoding process waiting codeword is a short codeword. Further, the value indicating the type of the next code table calculated by the short code word decoding speed-up unit 306 or the module for determining the type of the next code table provided individually is the short code word decoding speed The data can be stored in a register provided in the data conversion unit 306 or another storage device. For example, a storage device provided in the decryption unit 307 may be used.

Hereinafter, the decoding process in the decoding unit 307 according to the present embodiment will be described. A variable length code table for decoding the codeword waiting for decoding processing in the input code segment is held in the code table memory of the decoding unit 307. The decoding unit 307 searches the code table memory using the input code segment 302 as an index, and obtains a decoded codeword (run length / coefficient value) 312. For example, in the AVS standard, a variable length code table vlc0_intra for decoding a codeword is as shown in Table 13.

  Further, when the decoded codeword is acquired, the decoded codeword (run length / coefficient value) 312 is input to the code table selection / exponential Golomb code order generation unit 313, and the order of the exponent Golomb code of the long codeword (LCodeExpOrder) 309 is calculated and output. Similar to the exponent Golomb code order calculation method for the short codeword, the code table selection / exponential Golomb code order generation unit 313 determines the code table used by the next codeword based on the coefficient value decoded this time, and further To determine the exponent Golomb code order for requesting a codeword. From the above description, it should be understood by those skilled in the art that the code table selection / exponential Golomb code order generation unit 313 can include a logic circuit or a logic unit for realizing the above functions.

  In this embodiment, the information for requesting the next input code segment output from the decoding unit 307 is simply called the degree 309 of the exponent Golomb code of the long codeword. The code table selection / exponential Golomb code order generation unit 313 always performs the decoding from the decoded codeword to the exponential Golomb code regardless of whether the decoding-waiting codeword included in is a long codeword or a short codeword In order to calculate and output the order, the order of the exponent Golomb code of the long codeword output from the code table selection / exponential Golomb code order generation unit 313 actually includes the order of the exponent Golomb code of the short codeword. However, due to the presence of the selector 314, the order of the exponent Golomb code of the short codeword output from the code table selection / exponential Golomb code order generation unit 313 is not output to the exponent Golomb code decoder 311, that is, the short codeword Those skilled in the art will understand that the order of the exponent Golomb code is only the intermediate output information and does not affect the actual operation.

  In FIG. 3, the code table selection / exponential Golomb code order generation unit 313 is provided in the decoding unit 307, but actually, the code table selection / exponential Golomb code order generation unit 313 is provided outside the decoding unit 307. May be.

  The mode signal 304 output from the codeword identification unit 303 is input to the selector 314 to control the selector 314 so that the exponent Golomb code degree (ExpOrder) 310 is output to the exponent Golomb code decoder 311. For example, if the mode information 304 = “0”, the degree 308 of the exponent Golomb code of the short codeword is output via the selector 314, and the next input code segment is requested as the degree 310 of the exponent Golomb code. Otherwise, if mode information 304 = “1”, the degree 309 of the exponent Golomb code of the long codeword is output as the exponent 310 of the exponent Golomb code via the selector 314 to request the next input code segment. .

  The variable-length code decoding apparatus according to the present embodiment is different from the variable-length code decoding apparatus according to the prior art only in that a variable-length code decoding speed increasing module is added, so that the conventional variable-length code decoding apparatus is changed. It can be easily realized on the basis. However, the code table selection / exponential Golomb code order generation unit 313 calculates the exponent Golomb code order for acquiring the subsequent input code segment, regardless of whether the codeword waiting for decoding is a long codeword or a short codeword. To do. The degree of the exponent Golomb code of the short code word output from the code table selection / exponential Golomb code order generation unit 313 is not actually useful. Therefore, in another embodiment of the present invention, the variable length code decoding apparatus shown in FIG. 3 is improved.

  Next, a variable-length code decoding apparatus 401 for an AVS standard bitstream and its decoding processing according to another embodiment of the present invention will be described with reference to FIG. FIG. 4 shows a variable-length code decoding apparatus 401 for decoding an AVS-standard bitstream according to the present embodiment, and the same unit in the variable-length code decoding apparatus 301 of FIG. In the following description, description of the same modules as those in FIG. 3 will be omitted, and only differences from the variable-length code decoding apparatus 301 in FIG. 3 will be described.

  The variable-length code decoding apparatus 401 according to this embodiment differs from the variable-length code decoding apparatus 301 shown in FIG. 3 in that a switch 415 causes a decoding codeword to be code table selection / exponential Golomb code order generation unit 313. Control whether or not to input. ON / OFF of the switch 415 is controlled by a mode signal output from the code word identification unit 303. For example, when the mode signal = “0”, the switch 415 is turned off, and when the mode signal = “1”, the switch 415 is turned on. When the codeword waiting for decoding is a short codeword, the codeword identification unit 303 outputs mode signal = “0” and the switch 415 is turned off. In this case, the code table selection / exponential Golomb code order generation unit 313 Does not work. On the other hand, when the decoding process waiting codeword is a long codeword, the codeword identification unit 303 outputs mode signal = “1”, and the switch 415 is turned on. In this case, the decoding codeword (run length / engagement) is turned on. (Numerical value) 312 is input to the code table selection / exponential Golomb code order generation unit 313, so the code table selection / exponential Golomb code order generation unit 313 calculates the degree (LCodeExpOrder) 309 of the exponent Golomb code of the long codeword Output. Similar to FIG. 3, in FIG. 4, the code table selection / exponential Golomb code order generation unit 313 is provided in the decoding unit 407. It may be provided outside the conversion unit 407.

  The present invention is not limited to the above-described embodiments, and can be implemented by modifying a part of the configuration without departing from the gist of the present invention. For example, the variable length code decoding apparatus and method of the present invention can be applied to various variable length decoding standards other than the MPEG-2 / 4 / VC-1 standard and AVS standard described above, It should also be clear to those skilled in the art how to identify short codewords and how to calculate code segment request information for requesting an input code segment for different variable length decoding standards. is there.

  In addition, each module such as a codeword identification unit and a short codeword decoding speed-up unit mentioned in the above-described drawings and the description of the embodiment realizes a function corresponding to the module in the actual example of the present invention. There is a possibility that a storage unit, a control unit, a clock supply unit, and the like provided for the purpose are provided. Since the functions that can be realized by these units are well known to those skilled in the art, they are not described in detail in the description of the present invention. However, how to appropriately design and supply the above functional units from the functions described in the present invention. It should be clear to those skilled in the art what to do.

  Furthermore, each module disclosed in the present invention and a functional unit that supplies a corresponding function in these modules can be realized by software, hardware, or a combination of both, and any signal between the modules can be used. The format is acceptable. Each table referred to in this specification is only for expressing a mapping relationship, and is not necessarily a map table that is actually used. Further, the mapping relationship shown in each of these tables may be realized by a separate map table, or may be realized together with other tables as one map table. Furthermore, each module mentioned in the embodiment of the present invention may be realized separately, or may be realized by integration with other modules.

The preferred embodiment of the present invention has been described above, but the present invention is not limited to this embodiment, and all modifications to the present invention are within the scope of the present invention unless departing from the spirit of the present invention.
(Supplementary note 1) a codeword identification unit configured to determine whether a decoding process waiting codeword in an input code segment is a short codeword;
When the codeword identification unit determines that the codeword waiting for decoding processing is a short codeword, code segment request information is obtained until the decoding of the codeword waiting for decoding processing is completed, and the next input code A short codeword decoding acceleration unit configured to calculate code segment request information for requesting a next input code segment immediately to request a segment;
An apparatus for speeding up decoding of variable-length codes, including:
(Supplementary Note 2) The short codeword is a codeword having a length of N bits or less, and the N is a positive integer set in advance based on an average time required for decoding the codeword and a desired decoding speed. The variable-speed code decoding speed-up device according to attachment 1.
(Supplementary note 3) The variable-length code decoding speed-up device according to supplementary note 1, wherein the decoding-waiting codeword is a codeword encoded according to the MPEG-2, MPEG-4, or VC-1 standard.
(Supplementary note 4) The variable-length code decoding speed-up device according to supplementary note 3, wherein the code segment request information is the number of shift bits for acquiring the next input code segment.
(Additional remark 5) The said codeword identification unit checks the high-order bit in the said input code segment based on the encoding system of a variable length code, and the decoding process waiting codeword in the said input code segment is a short codeword. 4. The variable-speed code decoding speed-up device according to appendix 3, which determines whether there is any.
(Supplementary Note 6) The short codeword decoding speed-up unit is configured to output the number of shift bits corresponding to the decoding process waiting codeword determined to be a short codeword based on a variable-length code encoding method. The apparatus for speeding up decoding of a variable length code according to attachment 4, wherein
(Supplementary note 7) The variable-length code decoding speed-up device according to supplementary note 1, wherein the decoding-waiting codeword is a codeword encoded according to the AVS standard.
(Supplementary note 8) The variable-length code decoding speed-up device according to supplementary note 7, wherein the code segment request information is an order of an exponent Golomb code for obtaining the next input code segment.
(Supplementary note 9) The codeword identification unit compares the value of the input code segment with a predetermined threshold, and when the value of the input code segment is equal to or less than the predetermined threshold, the decoding process in the input code segment The variable-speed code decoding speed-up device according to appendix 7, wherein the waiting codeword is determined to be a short codeword.
(Supplementary Note 10) The short codeword is a codeword having a length of N bits or less, and the predetermined threshold is a maximum value that can be displayed by an N-bit exponential Golomb code. Decoding speed-up device.
(Supplementary note 11) When the decoding-waiting codeword is a short codeword, the short codeword decoding acceleration unit is based on a variable-length code encoding scheme and an exponent Golomb corresponding to the value of the input code segment 9. The variable-length code decoding speed-up device according to appendix 8, configured to acquire a code order.

201, 301, 401 Variable length code decoding apparatus 202, 302 Input code segment 203, 303 Code word identification unit 207, 306 Short code word decoding acceleration unit 208, 307, 407 Decoding unit 212 Barrel shifter 214, 314 Selector 311 Exponential Golomb Code Decoder 313 Code Table Selection / Exponential Golomb Code Degree Generation Unit

Claims (10)

A codeword identification unit configured to determine whether the decoding-waiting codeword in the input code segment is a short codeword;
When the codeword identification unit determines that the codeword waiting for decoding processing is a short codeword, code segment request information is obtained until the decoding of the codeword waiting for decoding processing is completed, and the next input code A short codeword decoding acceleration unit configured to calculate code segment request information for requesting a next input code segment immediately to request a segment;
A decoding speed-up device for variable-length codes,   The short codeword is a codeword having a length of N bits or less, and the N is a positive integer set in advance based on an average time required for decoding the codeword and a desired decoding speed. The variable-speed code decoding speed-up device as described.   2. The variable-length code decoding speed-up device according to claim 1, wherein the decoding processing waiting codeword is a codeword encoded according to MPEG-2, MPEG-4, or VC-1 standards.   4. The variable-length code decoding speed-up device according to claim 3, wherein the code segment request information is the number of shift bits for acquiring the next input code segment.   The codeword identification unit determines whether a codeword waiting for decoding in the input code segment is a short codeword by inspecting upper bits in the input code segment based on a variable length code encoding scheme. 4. The variable speed code decoding speed-up device according to claim 3, wherein:   The short codeword decoding acceleration unit is configured to output the number of shift bits corresponding to the decoding process waiting codeword determined to be a short codeword based on a variable-length code encoding method. Item 5. The variable speed code decoding speed-up device according to Item 4.   2. The variable speed code decoding speed-up device according to claim 1, wherein the decoding processing waiting codeword is a codeword encoded according to the AVS standard.   8. The variable-length code decoding speed-up device according to claim 7, wherein the code segment request information is an order of an exponent Golomb code for obtaining the next input code segment.   The codeword identification unit compares the value of the input code segment with a predetermined threshold value, and when the value of the input code segment is equal to or less than the predetermined threshold value, the codeword waiting for decoding in the input code segment is 8. The variable-length code decoding speed-up device according to claim 7, wherein the variable-length code decoding speed is determined to be a short code word.   10. The variable-length code decoding speedup according to claim 9, wherein the short codeword is a codeword having a length of N bits or less, and the predetermined threshold is a maximum value that can be displayed by an N-bit exponential Golomb code. apparatus.

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