CN101547353B - Decoding accelerator for variable length codes - Google Patents

Abstract

The invention provides a variable length code decoding acceleration device. The variable-length code decoding acceleration device includes: a codeword distinguishing unit configured to judge whether the codeword to be decoded in the input code segment is a short codeword; After the distinguishing unit judges that the code word to be decoded in the input code segment is a short code word, it immediately calculates the code segment request information for requesting the next input code segment, so that before the decoding of the code word to be decoded is completed The code segment request information is obtained to request the next input code segment. The variable-length code decoding acceleration device according to the present invention can be used in a variable-length code decoding device, for example, to improve the decoding speed of the entire variable-length code decoding device by accelerating the decoding of short codewords with a higher frequency of occurrence .

Description

Variable length code decoding acceleration device

technical field

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

Background technique

Variable length code decoder is an important part of video decoder. The encoder uses codewords of different lengths to encode according to the frequency of symbols in the code stream. Symbols with high frequency of occurrence are encoded with shorter codewords, and symbols with low frequency of occurrence are encoded with longer codewords. Since the length of the codeword is not fixed, the entire decoding process has high interdependence, so it is difficult to speed up the decoding speed through parallel processing. The most commonly used variable length code decoding method is the look-up table method. In this method, a code segment with a fixed number of bits is read from the code stream as an index to search in the code table. In addition, in order to reduce the size of the code table and speed up the search speed of the code table, some optimization methods such as multi-level look-up table are proposed. These optimization methods, such as the U.S. Patent No. 5,253,053 published on October 12, 1993 titled "Variable length decoding using lookup tables", disclose a variable length code decoding method using two or more levels of lookup tables, and U.S. Patent No. 6,011,498, entitled "Dual-speed variable length decoding architecture for MPEG-2 video data" published on January 4, 2000, uses a high-speed look-up table alone to determine the main data in an MPEG-2 video stream : Method of DCT coefficients for decoding MPEG video data. The entire contents of these related patents are hereby incorporated by reference.

As mentioned above, in the commonly used variable-length code decoding method using a lookup table, it usually includes three main steps or stages: 1. Request code segment: the decoder will output at this stage for requesting the next input code segment Code segment request information, for example, for the MPEG-2/4/VC-1 standard, the decoder outputs the number of shifted bits of the barrel shifter to the barrel shifter, or for the AVS standard, the decoder uses the exponential Columbus code order output to the Exponential Golomb code decoder to request the next input code segment; 2. Obtain the code segment: at this stage, the unit for generating the next input code segment such as the barrel shifter/Expo Golomb code decoder will The next input code segment will be generated to the decoder according to the number of shifted bits/exponential Columbus code order, etc.; 3. Decoding codeword: At this stage, the input code segment will be used as an index to retrieve the coded code in the code table and the information needed to decode the next codeword (ie, request the next input code segment) (eg, barrel shifter shift bits or Exponential Golomb code order). The above three steps are executed sequentially, as shown in Figure 5, the phases of requesting a code segment and obtaining a code segment usually take up one clock cycle respectively, and since the code tables in video standards are very large, they are usually stored in static memory, and the search code The table, that is, the decoding codeword stage usually takes more than two clock cycles, so the time to access the memory greatly exceeds the time required to request a code segment and obtain a code segment. Therefore, the speed of variable-length code decoding mainly depends on the time of looking up the code table. For longer codewords, since enough bits are decoded, the larger time delay required to access the memory is acceptable. But for short codewords, too slow decoding speed will reduce the performance of the whole decoder.

Aiming at the above problem that the decoding speed of short codewords affects the performance of the entire decoder, the present invention proposes a decoding method that treats decoding of long codewords and short codewords differently, thereby improving the decoding speed of the entire variable-length code decoder.

Contents of the invention

According to one aspect of the present invention, a variable-length code decoding acceleration device is provided, the device includes: a codeword distinguishing unit configured to determine whether the codeword to be decoded in the input code segment is a short codeword; and a short codeword The word decoding acceleration unit is configured to calculate the code segment request information for requesting the next input code segment immediately after the code word distinguishing unit judges that the code word to be decoded is a short code word, so that the decoding of the code word to be decoded Get a code segment request message to request the next input code segment before completion.

According to the present invention, preferably, a short codeword is a codeword with a length less than or equal to N bits, where N is based on the average time required to decode the codeword and the expected decoding speed without optimizing the short codeword A preset positive integer.

According to the present invention, preferably, the codeword to be decoded is a codeword encoded according to the MPEG-2, MPEG-4 or VC-1 standard. In this case, the segment request information is the number of shifted bits for obtaining the next input segment. The code word distinguishing unit judges whether the code word to be decoded in the input code segment is a short code word by checking the upper bits in the input code segment according to the variable-length code coding rule. The short codeword decoding acceleration unit is configured to output the number of shifted bits corresponding to the codeword to be decoded as the short codeword according to the variable length code coding rule.

According to the present invention, preferably, the codeword to be decoded is a codeword coded according to the AVS standard. In this case, the code segment request information is the order of the Exponential Golomb code used to obtain the next input code segment. The codeword distinguishing unit compares the value of the input code segment with a predetermined threshold, and when the value of the input code segment is less than or equal to the predetermined threshold, the code word distinguishing unit judges that the codeword to be decoded in the input code segment is a short code word. In addition, preferably, the short codeword is a codeword with a length less than or equal to N bits, and the predetermined threshold is the maximum value that can be represented by an N-bit exponential Golomb code. Furthermore, the short codeword decoding acceleration unit is configured to obtain the exponential Golomb code order corresponding to the value of the input code segment according to the variable length code coding rule when the codeword to be decoded is a short codeword.

Therefore, the variable-length code decoding acceleration device according to the present invention can be applied in a variable-length code decoding device, for example, to accelerate the decoding of short codewords with a higher frequency of occurrence, thereby greatly improving the decoding performance of the variable-length code decoder. speed.

Description of drawings

For a more complete understanding of the present invention, reference is now made to the following description taken in conjunction with the accompanying drawings, in which like reference numerals will be used to designate like or similar parts throughout:

Fig. 1 shows the variable length code decoding process according to the present invention;

Fig. 2 shows a variable length code decoding device that can be used to decode a code stream of the MPEG-2/4/VC-1 standard according to an embodiment of the present invention;

FIG. 3 shows a variable length code decoding device that can be used to decode a code stream of the AVS standard according to another embodiment of the present invention;

FIG. 4 shows a variable length code decoding device that can be used to decode a code stream of the AVS standard according to another embodiment of the present invention;

Fig. 5 shows a variable length code decoding process in the prior art.

Detailed ways

Specific embodiments of a variable length code decoding device according to the present invention will be described below with reference to FIG. 1 to FIG. 4 . In the following description, the present invention is described for the commonly used MPEG-2/4/VC-1 standard and AVS standard in video compression codec respectively, but those skilled in the art should understand that this description is only for the purpose of illustration, and The compression codec standard applicable to the present invention is not limited thereto, for example, it may also be JPEG standard, CCITT standard or any other variable length codec standard.

Fig. 1 shows the decoding process of a variable length code according to the present invention, wherein the upper part shows the decoding process in which the codeword to be decoded in the input code segment is a short code word, and the lower part shows the decoding process in the input code segment The codeword to be decoded is the decoding process of the long codeword.

Before describing FIG. 1 , a brief description of the terms input code segment and codeword to be decoded in the present invention is given first. Usually, the variable-length code stream can be divided into fixed-length code segments one by one, and then these code segments are continuously input into the decoder for decoding. Each fixed-length input code segment may contain one or more variable-length code words coded according to variable-length code rules. When the decoder decodes an input code segment, it generally only decodes an encoded code word starting from the highest bit of the input code segment, and the rest of the undecoded bits in the input code segment will be used by the decoder for subsequent input codes The segment is decoded when it is decoded. Therefore, these fixed-length code segments are referred to as input code segments in the present invention, and a coded code word with a variable length that is actually decoded from the highest bit of the input code segment is referred to as a code word in the input code segment The codeword to be decoded.

As shown in Figure 1, in order to speed up the decoding of variable-length codes, when calculating the code segment request information for requesting the next input code segment, the input code segment and the code word to be decoded for which the code word to be decoded is a short code word Different calculation methods are adopted for the input code segment of the long code word. For the case where the codeword to be decoded is a short codeword, after obtaining the current input code segment, while decoding the code word to be decoded in the input code segment, a dedicated circuit can be used to calculate the code used to request the next input code There is no need to obtain the code segment request information by accessing the code table memory, so that the code segment request information can be obtained before the code word to be decoded is decoded to request the next code segment. Therefore, the stage of requesting the next code segment does not start after the decoding of the codeword to be decoded is completed, but is carried out in parallel with the decoding codeword stage, thereby accelerating the decoding speed of short codewords. For the case where the codeword to be decoded is a long codeword, the code segment request information for requesting the next code segment is still obtained in the decoding stage, and the next code segment is requested after the decoding is completed. According to the present invention, since the decoding speed of short codewords with higher frequency of occurrence is greatly increased, the entire variable-length code decoding process is accelerated. Here, it should be noted that in FIG. 1 , only schematically shows the relative relationship between the execution time of each operation stage in the decoding process under normal circumstances, and this illustration should not be interpreted as a reference to each operation of the present invention. The execution time of the stage is limited, as long as the decoding process conforms to the general idea of the present invention.

A variable-length code decoding device and its decoding process for a code stream of the MPEG-2/4/VC-1 standard according to an embodiment of the present invention will be described below with reference to FIG. 2 . Fig. 2 shows a variable length code decoding device 201 for decoding MPEG-2/4/VC-1 video streams according to this embodiment. The input of the variable length code decoding device 201 is an input code segment (InCodSeg) 202 with a fixed length outputted by a barrel shifter 212 . The codeword to be decoded in the input code segment 202 is decoded in the variable length code decoding device 201 to generate a decoded codeword (DecCode) 213 . The variable length code decoding device shown in FIG. 2 adopts the decoding process shown in FIG. 1 . In order to realize the decoding process, for the case where the codeword to be decoded is a short codeword, the code segment request information used to request the next code segment will be calculated by the short codeword decoding acceleration unit 207 instead of accessing the decoding The code table memory in the unit 208 is obtained. The specific operations of each functional unit in FIG. 2 during the decoding process will be described in detail below.

In the variable length code decoding device 201, after the input code segment 202 is obtained from the barrel shifter 212, the input code segment 202 is input to the decoding unit 208 for decoding, and the input code segment 202 is also input to the code word distinguishing Unit 203. In the codeword distinguishing unit 203, it is judged whether the codeword to be decoded in the input code segment 202 is a long codeword (codeword length greater than N) or a short codeword (codeword length less than or equal to N). If the codeword to be decoded in the input code segment 202 is judged to be a short code word, the code word distinguishing unit 203 inputs the input code segment 202 to the short code word decoding acceleration unit 207 via the short code word signal (SCode) 205 .

Here, the value of N can be based on the average time required to decode a codeword (number of clock cycles) and the required decoding speed (bits/clock cycle) under normal conditions (that is, without accelerating the decoding of short codewords) to preset. For example, in the case where a decoding speed of at least 1 bit/clock cycle is required, and decoding a codeword takes an average of 5 clock cycles, if the decoding of short codewords is not optimized, the decoding speed of codewords less than 5 bits in length It will be lower than 1 bit/clock cycle, so we can set codewords with codeword length less than 5 (ie N=4) as short codewords for optimization. Note that the description about setting the value of N here is also applicable in other embodiments.

According to the encoding rules stipulated in the MPEG-2/4/VC-1 standard, the codeword distinguishing unit 203 can use the following matching mechanism to determine whether the codeword to be decoded in the input code segment is a short codeword. For example, N=4, then from the highest bit of the input code segment, the input code segment is compared with a code word with a length less than or equal to 4 bits specified by the encoding rule, to judge whether the code word to be decoded in the input code segment is short codeword. For example, in the MPEG-2 standard, the judgment rule of the short codeword can be specified as follows according to the settings in the MPEG-2 standard. When the decoding code table is DCT coefficient table 0, the judgment rules of short codewords are shown in Table 1-1, and when the decoding code table is DCT coefficient table 1, the judgment rules of short codewords are shown in Table 1 -2 shown. Note that the tables presented in this article are just to represent the mapping mechanism, not the actual stored mapping table.

Table 1-1

Enter the high four digits of the code segment The length of the codeword to be decoded Whether the codeword to be decoded is a short codeword 10xx 2 bits yes 11xx 2 bits yes 011x 3 bits yes 0100 4 bits yes 0101 4 bits yes other ＞4 bits no

Table 1-2

Enter the high four digits of the code segment The length of the codeword to be decoded Whether the codeword to be decoded is a short codeword 10xx 2 bits yes 010x 3 bits yes 110x 3 bits yes 0111 4 bits yes 0110 4 bits yes other ＞4 bits no

Among them, "x" means that the bit is '0' or '1'.

When the decoding code table is DCT coefficient table 0, as shown in Table 1-1, if the highest two bits of the input code segment are 10 or 11, then according to the MPEG-2 standard, the code word to be decoded is 10 or 11 , the code word length is 2 bits, so the code word to be decoded can be judged as a short code word; if the highest three bits of the input code segment are 011, the code word to be decoded is 011, and the code word length is 3 bits, Thereby this code word to be decoded can be judged as short code word; If the highest four bits of the input code segment are 0100 or 0101, then the code word to be decoded is 0100 or 0101, and its code word length is 4 bits, so the code word to be decoded The word can be judged as a short codeword; if the input code segment is otherwise, then according to the MPEG-2 standard, the length of the codeword to be decoded is greater than 4 bits, so the codeword to be decoded can be judged to be a long codeword. Similarly, in the case where the current decoding code table is DCT coefficient table 1, as shown in Table 1-2, if the highest two bits of the input code segment are 10, then according to the MPEG-2 standard, the code word to be decoded is 10, The code word length is 2 bits, so the code word to be decoded can be judged as a short code word; if the highest three bits of the input code segment are 010 or 110, the code word to be decoded is 010 or 110, and the code word length is 3 bits, so that the codeword to be decoded can be judged as a short codeword; if the highest four bits of the input code segment are 0111 or 0110, the codeword to be decoded is 0111 or 0110, and the codeword length is 4 bits, so the codeword to be decoded Words can be determined as short codewords; if the input code segment is otherwise, according to the MPEG-2 standard, the length of the actual decoded codeword is greater than 4 bits, so the codewords to be decoded in these input code segments can be determined is a long code word.

As mentioned above, the codeword distinguishing unit 203 can judge whether the codeword to be decoded in the input code segment is a short code word according to the variable length code encoding rule, specifically, according to the type of the current decoding code table and the input code segment 202 from At most N bits starting from the most significant bit are used to determine whether the codeword to be decoded in the input code segment 202 is a short codeword whose length is less than or equal to N bits. For example, those skilled in the art can design a logic circuit in the codeword distinguishing unit 203 to start from the most significant bit of the input code segment and the code word with a length less than or equal to N bits specified in the current decoding code table. Once it is found to match a certain short codeword in the current decoding code table, the judgment process can end immediately. Therefore, the actual number of bits in the input code segment to be compared here is at most 4 bits starting from the most significant bit.

Note that the decision rules shown in Tables 1-1 and 1-2 are only exemplary decision rules when the codec standard is the MPEG-2 standard, and those skilled in the art should easily -1 etc. to similarly set the short codeword decision rules applicable in these codec standards.

According to the above decision rules, the codeword distinguishing unit 203 has two outputs: a mode signal (Mode) 204 and a short codeword signal (SCode) 205 . The mode signal 204 indicates whether the codeword to be decoded in the input code segment 202 is a short codeword (eg, mode signal="0") or a long codeword (eg, mode signal="1"). If the mode signal indicates that the codeword to be decoded in the input code segment 202 is a short code word, the code word distinguishing unit 203 outputs the input code segment 202 to the short code word decoding acceleration unit 207 via the short code word signal 205 .

As mentioned above, for the input code segment whose code word to be decoded is a long code word and the input code segment whose code word to be decoded is a short code word, the code segment request information for requesting the next input code segment is calculated in different implemented in the unit. In this embodiment, the code segment request information is the number of shifting bits of the barrel shifter 212 . Specifically, for the input code segment 202 whose codeword to be decoded is judged to be a short codeword, the short codeword decoding acceleration unit 207 calculates and outputs the short codeword shift number (SCodeSBitNum) 209 according to the short codeword signal 205, For the input code segment 202 whose code word to be decoded is determined to be a long code word, the decoding unit 208 accesses the code table memory according to the input code segment 202 to obtain and output the long code word shift number (LCodeSBitNum) 210 .

The following describes the process of the short codeword decoding acceleration unit 207 calculating the number of shifted bits of the short codeword. The number of shift bits is the length of the codeword to be decoded in the current input code segment. In this embodiment, a mapping mechanism can be used to calculate the length of the codeword to be decoded in the input code segment, that is, to calculate the input The length of the codeword to be decoded in the code segment. For example, in the MPEG-2 standard, when the current decoding code table is DCT coefficient table 0, the mapping mechanism for calculating the shift number of short codewords is shown in Table 2-1, while the current decoding code table is DCT coefficient table 0 In the case of Table 1, the mapping mechanism for calculating the shift number of short codewords is shown in Table 2-2. In addition, those skilled in the art should be clear that, in the case of other codec standards, a similar mapping mechanism can be set according to the coding rules stipulated in these standards to calculate the short codeword shift number 209 .

table 2-1

Enter the high four digits of the code segment bit shift 10xx 2 11xx 2 011x 3 0100 4

0101 4

Table 2-2

Enter the high four digits of the code segment bit shift 10xx 2 010x 3 110x 3 0111 4 0110 4

Note that, as mentioned above, although the operations of the codeword distinguishing unit 203 and the short codeword decoding acceleration unit 207 are all related to the type of the current decoding code table, those skilled in the art should be clear that for the MPEG-2/4 standard, the current The type of the decoding code table is determined by other modules in the video decoder. For the variable length code decoder, it does not change frequently, but is equivalent to a fixed parameter. Therefore, in the actual implementation, the code word The distinguishing unit 203 and the short codeword decoding acceleration unit 207 only need to receive the current decoding code table type information from the outside (not shown in the figure), and select and use the appropriate mapping relationship according to the above-described method according to the information.

The following describes the decoding process performed in the decoding unit 208 according to this embodiment. In the decoding code word stage, the decoding unit 208 uses the input code segment 202 as an index to look up the variable-length code code table in the code table memory to obtain the decoded code word (DecCode) (run length/coefficient value) 213 and for requesting The long code word shift bit 210 of an input code segment. The decoding unit 208 can use a common decoding unit in the prior art, therefore, the variable-length code decoding acceleration device according to the present invention can be easily applied to an existing variable-length code decoding device.

For example, according to MPEG-2, for DCT coefficient table 0, the mapping table stored in the code table memory for decoding and generating the number of shifted bits is shown in Table 3.

table 3

00101xxx 0 3 5 00111xxx 3 1 5 00110xxx 4 1 5 000110xx 1 2 6 000111xx 5 1 6 000101xx 6 1 6 ...  …  …

Among them, "x" means that the bit can be '0' or '1'.

It should be noted that although the information for requesting the next input code segment output by the decoding unit 208 is simply referred to as the long code word shift number 210, since the decoding unit 208 according to this embodiment uses the existing It is implemented by a general decoding unit in the technology, so no matter whether the codeword to be decoded in the input code segment is a long codeword or a short codeword, the decoding unit 208 will output the number of shifted bits after the decoding is completed, so the output of the decoding unit 208 The long codeword shift number 210 actually also includes the short codeword shift number. However, those skilled in the art should understand that due to the existence of the gate 214, the short code word shifted digits output by the decoding unit 208 will not be output to the barrel shifter 211, that is to say, the short code word The number of word shift bits is only intermediate output information, and has no effect on actual operation.

In addition, the mode signal 204 output by the codeword distinguishing unit 203 is input to the gate 214 to control the gate 214 to output the short codeword shift number 209 or the long codeword shift number 210 to the barrel shifter. bit register 212. For example, if the mode signal="0", the short code word shift number 209 is output as the shift number (SbitNum) 211 via the gate 214 to request the next input code segment; otherwise, if the mode signal=" 1", the long codeword shift number 210 is output as the shift number 211 via the gate 214 to request the next input code segment.

The following describes a variable length code decoding apparatus 301 for a code stream of the AVS standard and its decoding process according to another embodiment of the present invention with reference to FIG. 3 . FIG. 3 is a variable length code decoding device 301 for decoding a code stream of the AVS standard. The input of the variable length code decoding device 301 is the input code segment (InCodSeg) 302 with a fixed number of bits output by the exponential Golomb code decoder 311 . The codeword to be decoded in the input code segment 302 is decoded in the variable length decoding device 301 to generate a decoded codeword (DecCode) 312 . The variable length code decoding device 301 also adopts the decoding process as shown in FIG. 1 . In order to realize the decoding process, the code segment request information for requesting the next code segment (in this embodiment, the code segment request information is the exponential Golomb code order) will be calculated by the short codeword decoding acceleration unit 306, Instead of getting it after decoding is complete.

In the variable length code decoding device 301, after obtaining the input code segment 302 from the exponential Golomb code decoder 311, the input code segment 302 is input to the decoding unit 307 to decode the codeword to be decoded therein, and the input code segment 302 is also input to the codeword distinguishing unit 303. In the codeword distinguishing unit 303, it is judged whether the codeword to be decoded in the input code segment 302 is a long codeword (codeword length greater than N bits) or a short codeword (codeword length less than or equal to N bits). Then, if the code word distinguishing unit 303 judges that the code word to be decoded in the input code segment 302 is a short code word, then the code word distinguishing unit 303 inputs the input code segment 302 to the short code word via the short code word signal (SCode) 305 Decoding acceleration unit 306 .

The codeword distinguishing unit 303 can judge whether the codeword to be decoded in the input code segment is a short code word 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 by the exponential Golomb code decoder, and its value is the decimal number represented by the bit stream, so the value of the input code segment is easy to determine. If the numerical value of the input code segment is less than or equal to the predetermined threshold, it is determined that the code word to be decoded in the input code segment is a short code word; on the contrary, if the numerical value of the input code segment is greater than the predetermined threshold, then it is determined that the code word to be decoded in the input code segment The decoded codeword is a long codeword. For example, N=4, since the maximum number that can be represented by 4-bit exponential Golomb code is 7, the threshold can be set as 7, so the decision rules are shown in Table 4. If the value of the input code segment is less than or equal to 7, the codeword to be decoded in the input code segment is judged as a short code word; and if the value of the input code segment is greater than 7, the codeword to be decoded in the input code segment is judged is a long codeword.

Table 4

Enter the value of the code segment Whether the codeword to be decoded is a short codeword ＜＝7 yes ＞7 no

Note that according to the coding rules of the Exponential Golomb code, in fact, when the value of the input code segment<=7, the codeword to be decoded in the input code segment may also be a code word with a length greater than 4 bits. However, this situation is relatively rare, and even if some codewords with a length greater than 4 bits are judged as short codewords and optimized, it will not affect the effect of this embodiment, because the present invention only needs to ensure that the length is less than or equal to It is sufficient that the decoding of the 4-bit codeword is optimized.

There are two outputs of the codeword distinguishing unit 303 : a mode signal (Mode) 304 and a short codeword signal (SCode) 305 . The mode signal 304 indicates whether the codeword to be decoded in the current input code segment 302 is a short codeword (eg, mode signal="0") or a long codeword (eg, mode signal="1"). If the mode signal indicates that the codeword to be decoded in the input code segment 302 is a short code word, the code word distinguishing unit 303 outputs the input code segment 302 to the short code word decoding acceleration unit 306 via the short code word signal 305 .

The short codeword decoding acceleration unit 306 calculates a short codeword exponential Golomb order (SCodeExpOrder) 308 according to the value of the input code segment 302 input via the short codeword signal 305 .

In the AVS standard, the order of the Exponential Golomb code is determined by the code table used for decoding. Before describing the specific operation process of the short codeword decoding acceleration unit 306, the following briefly explains the principle of determining the order of the short codeword Exponential Golomb code according to the AVS standard.

According to the coding rules stipulated in the AVS standard, the corresponding relationships shown in Table 5-1 to Table 5-3 can be obtained, and the next code table can be known according to the value of the code segment and the current code table.

Table 5-1

Table 5-2

0 Vlc1_inter vlc1_inter vlc2_inter vlc3_inter vlc4_inter vlc5_inter vlc6_inter 1 Vlc1_inter vlc1_inter vlc2_inter vlc3_inter vlc4_inter vlc5_inter vlc6_inter 2 Vlc1_inter vlc1_inter vlc2_inter vlc3_inter vlc4_inter vlc5_inter vlc6_inter 3 Vlc1_inter vlc1_inter vlc2_inter vlc3_inter vlc4_inter vlc5_inter vlc6_inter 4 Vlc1_inter vlc1_inter vlc2_inter vlc3_inter vlc4_inter vlc5_inter vlc6_inter 5 Vlc1_inter vlc1_inter vlc2_inter vlc3_inter vlc4_inter vlc5_inter vlc6_inter 6 Vlc1_inter vlc1_inter vlc2_inter vlc3_inter vlc4_inter vlc5_inter vlc6_inter 7 Vlc1_inter vlc1_inter vlc2_inter vlc3_inter vlc4_inter vlc5_inter vlc6_inter

Table 5-3

According to the encoding rules in the AVS standard, the order of the Exponential Golomb code corresponds to the code table used. Therefore, the mapping relationship shown in Table 6-1 to 6-3 can be obtained, where the order of the Exponential Golomb code can be determined according to the value of the code segment and the current code table.

Table 6-1

2 2 2 2 2 2 2 2 3 2 2 2 2 2 2 2 4 2 2 2 2 2 2 2 5 2 2 2 2 2 2 2 6 2 2 2 2 2 2 2 7 2 2 2 2 2 2 2

Table 6-2

Table 6-3

7 0 0 1 1 0

Utilizing the above characteristics of the AVS standard, the short codeword decoding acceleration unit 306 according to this embodiment can obtain the exponential Golomb code order of the short codeword to be decoded according to the current code table and code segment values. The operations performed in the short codeword decoding acceleration unit 306 according to this embodiment will be described in detail below.

When the codeword distinguishing unit 303 determines that the codeword to be decoded in the input code segment 302 is a short code word, the input code segment 302 is input to the short code word decoding acceleration unit 306 via the short code word signal 305 . Then, the short codeword decoding acceleration unit 306 can calculate the information for requesting the next input code segment according to the mapping relationships shown in Tables 6-1 to 6-3, that is, the short codeword exponential Golomb code order 308.

In addition, the short code word decoding acceleration unit 306 also determines the next code table type according to the mapping relationship shown in Table 5-1 to 5-3, and saves the determined next code table type, so as to be used in the next waiting The operation when the decoded codeword is a short codeword. That is to say, when the previous codeword to be decoded is a short codeword, the short codeword decoding acceleration unit 306 uses the stored code table type determined last time to determine the Exponential Golomb code order of the current codeword to be decoded. number and the next stopwatch type. In addition, in the case where the previous codeword to be decoded is a long codeword, the short codeword decoding acceleration unit 306 selects/exponential Golomb code order from the code table in the decoding unit 307 via the code table type identification signal (CodTabIdf) 315 The code table type received by the generation unit 313 is used to determine the Exponential Golomb code order and the next code table type of the current codeword to be decoded. Those skilled in the art can easily understand that, for example, the mode signal 304 can be used to control the short codeword decoding acceleration unit 306 to select and use an appropriate code table type identifier.

The above mapping relationships shown in Tables 5-1 to 5-3 and Tables 6-1 to 6-3 may be stored or programmed in the short codeword decoding acceleration unit 306, or stored in other storage devices. For example, when the code word to be decoded is a short code word, the module for determining the next code table type can also be provided separately outside the short code word decoding acceleration unit 306, and then the code table type determined by the module is input to the short codeword decoding acceleration unit 306 for its operation when the next codeword to be decoded is a short codeword. In addition, the value representing the next code table type calculated by the short code word decoding acceleration unit 306 or a separately arranged module for determining the next code table type can be stored in a register arranged in the short code word decoding acceleration unit 306 In, or in other storage devices, for example, a storage device provided in the decoding unit 307 may be used.

The following describes the decoding process in the decoding unit 307 according to the present embodiment. The variable-length code code table used for decoding the codeword to be decoded in the input code segment is stored in the code table memory in the decoding unit 307 . The decoding unit 307 uses the input code segment 302 as an index to search the variable-length code table in the code table memory to obtain a decoded code word (run/coefficient value) 312 . For example, in the AVS standard, the variable length code table vlc0_intra used for decoding codewords is shown in Table 7.

Table 7

In addition, after obtaining the decoded codeword, the decoded codeword (run/coefficient value) 312 will be input into the code table selection/expo-Golomb code order generating unit 313 to calculate and output the long codeword exponent-Golomb code order ( LCodeExpOrder) 309. Similar to the calculation method of the exponential Golomb code order for short codewords, the code table selection/expo Golomb code order generation unit 313 determines the code table to be used for decoding the next codeword by the coefficient value obtained by current decoding, and then Determines the order of the Exponential Golomb code used to request the next codeword. According to the above description, those skilled in the art should understand that the code table selection/expo-Golomb code order generation unit 313 may include logic circuits or logic units for realizing the above functions.

It should be noted that, in this embodiment, although the information for requesting the next input code segment output by the decoding unit 307 is simply called the long codeword exponential Golomb code order 309, since in this embodiment , regardless of whether the codeword to be decoded contained in the input code segment is a long codeword or a short codeword, the code table selection/expo-Golomb code order generation unit 313 will calculate and output the exponential-Golomb code order according to the decoded codeword after decoding is completed Therefore, the long code word Exponential Golomb code order output by the code table selection/Expo Golomb code order generation unit 313 actually includes the short code word Exponential Golomb code order. However, those skilled in the art should understand that due to the existence of the gate 314, the short code word Exponential Golomb code order output by the code table selection/Expo Golomb code order generating unit 313 will not be output to the Exponential Golomb code decoding device 311, that is to say, the order of the short codeword Exponential Golomb code is only intermediate output information, and has no effect on actual operation.

Note that although in FIG. 3 , the code table selection/expo-Golomb code order generation unit 313 is provided inside the decoding unit 307, in fact the code table selection/expo-Golomb code order generation unit can also be provided in the decoding unit. Exterior of unit 307.

In addition, the mode signal 304 output by the codeword distinguishing unit 303 is input to the gate 314 to control the exponential Golomb order (ExpOrder) 310 output from the gate 314 to the exponential Golomb decoder 311 . If the mode signal = "0", the short codeword Exponential Golomb order 308 will be output via the gate 314 as the Exponential Golomb order 310 to request the next input code segment; otherwise, if the mode signal = "1" , then the long codeword Exponential Golomb order 309 will be output as the Exponential Golomb order 310 via the gate 314 to request the next input code segment.

Compared with the variable length code decoding device in the prior art, the variable length code decoding device according to this embodiment only adds a variable length code decoding acceleration module, so it is easy to implement based on the existing variable length code decoding device accomplish. But, because in the code table selection/exponential Golomb code order generating unit 313, no matter whether the codeword to be decoded is a long codeword or a short codeword, the exponential Golomb code order for obtaining the latter input code segment will be calculated, and The exponent-Golomb code order of the short code word output by the code table selection/expo-Golomb code order generating unit 313 actually has no effect. Therefore, in another embodiment of the present invention, the variable length code decoding device shown in FIG. 3 is improved.

The following describes a variable length code decoding apparatus 401 for a code stream of the AVS standard and its decoding process according to another embodiment of the present invention with reference to FIG. 4 . Fig. 4 shows a variable-length code decoding device 401 for decoding a code stream of the AVS standard according to the present embodiment, wherein the same symbols are used to indicate the same units as in the variable-length code decoding device 301 shown in Fig. 3 and signals, and in the following description, the description about the same modules as in FIG. 3 is omitted, and only the differences between the variable length code decoding apparatus shown in FIG. 4 and FIG. 3 are described.

The difference between the variable-length code decoding device 401 according to this embodiment and the variable-length code decoding device 301 shown in FIG. Unit 313. The opening/closing of the switch 415 is controlled by the mode signal output by the codeword distinguishing unit 303 . For example, if the mode signal = "0", the switch 415 is open, and if the mode signal = "1", the switch 415 is closed. When the codeword to be decoded was a short codeword, the codeword distinguishing unit 303 output mode signal="0", thereby switch 415 was disconnected, and now the code table selection/exponential Golomb code order generation unit 313 was not working, and when When the codeword to be decoded is a long codeword, the codeword distinguishing unit 303 output mode signal="1", thereby making the switch 415 closed, and now the decoded codeword (run/coefficient value) 312 will be input to the code table selection/ The Exponential Golomb code order generating unit 313, therefore the code table selection/Expo Golomb code order generating unit 313 will calculate and output the long code word Exponential Golomb code order (LCodeExpOrder) 309. Note that, similar to FIG. 3, although the code table selection/expo-Golomb code order generation unit 313 is also provided inside the decoding unit 407 in FIG. 4, in fact the code table selection/expo-Golomb code order generation unit is also may be provided outside the decoding unit 407.

The present invention is not limited to the above-mentioned embodiments, and the present invention can be implemented by modifying part of the configuration within the scope not departing from the spirit of the present invention. For example, the variable-length code decoding device and method of the present invention can be used in various variable-length codec standards other than the above-described MPEG-2/4/VC-1 standard and AVS standard, and those skilled in the art Personnel should be aware of how to identify short codewords and calculate code segment request information for requesting input code segments for different criteria.

In addition, the various modules mentioned in the above drawings and descriptions of related embodiments, such as the codeword distinguishing unit, short codeword decoding acceleration unit, etc., may include Set storage unit, control unit, clock supply unit, etc. The functions that these units can realize are well known to those skilled in the art, so they are not specifically described in the description of the present invention, but those skilled in the art should be clear how to properly design and provide these units according to the functions described in the present invention. functional unit. In addition, the various modules disclosed in the present invention and the functional units providing corresponding functions in these modules can be realized by software, hardware or their combination, and the signals between the various modules can be transmitted in any possible way.

In addition, it should be noted that the various tables mentioned in the specification are only to indicate the mapping relationship, but not necessarily the actual mapping table used, and the mapping relationship represented by each of these tables can be mapped with a separate table, or combined with other tables in a mapping table. Moreover, each module mentioned in the embodiment of the present invention may be implemented independently, or may be appropriately integrated with other modules for implementation.

In summary, the description of the above embodiments of the present invention is only used to help understand the method of the present invention and its core idea, and does not intend to limit the scope of the present invention; meanwhile, for those of ordinary skill in the art, according to the idea of the present invention, There are also various changes and modifications in the specific implementation and application range, and these changes and modifications all fall within the scope of the present invention defined by the appended claims.

Claims (11)

1. A variable-length code decoding acceleration device, characterized in that it comprises: A codeword distinguishing unit configured to determine whether the codeword to be decoded in the input code segment is a short codeword; and The short codeword decoding acceleration unit is configured to calculate the code segment request information for requesting the next input code segment immediately after the codeword distinguishing unit judges that the codeword to be decoded is a short codeword, so that The code segment request information is obtained before the decoding of the codeword to be decoded is completed to request a next input code segment. 2. The variable-length code decoding acceleration device as claimed in claim 1, wherein the short codeword is a codeword with a length less than or equal to N bits, and the N is the average time required according to the decoding codeword and the required The desired decoding speed is a preset positive integer. 3. The variable length code decoding acceleration device according to claim 1, wherein the codeword to be decoded is a codeword encoded according to the MPEG-2, MPEG-4 or VC-1 standard. 4. The variable-length code decoding acceleration device according to claim 3, wherein the code segment request information is the number of shifted bits used to obtain the next input code segment. 5. The variable-length code decoding acceleration device as claimed in claim 3, wherein the codeword distinguishing unit judges that in the input code segment by checking the high-order bits in the input code segment according to the variable-length code encoding rule Whether the codeword to be decoded is a short codeword. 6. The variable-length code decoding acceleration device according to claim 4, wherein, the short codeword decoding acceleration unit is configured to output and be judged as the short codeword according to the coding rule of the short codeword The number of shift bits corresponding to the decoded codeword. 7. The variable-length code decoding acceleration device according to claim 1, wherein the codeword to be decoded is a codeword coded according to the AVS standard. 8. The variable-length code decoding acceleration device according to claim 7, wherein the code segment request information is an order of the Exponential Golomb code used to obtain the next input code segment. 9. The variable-length code decoding acceleration device according to claim 7, wherein the codeword distinguishing unit compares the value of the input code segment with a predetermined threshold, and when the value of the input code segment is less than or When equal to the predetermined threshold, the codeword distinguishing unit judges that the codeword to be decoded in the input code segment is a short codeword. the 10. The variable-length code decoding acceleration device as claimed in claim 9, wherein the short codeword is a codeword with a length less than or equal to N bits, and the predetermined threshold is what can be represented by an N-bit exponential Golomb code maximum value. the 11. The variable-length code decoding acceleration device according to claim 8, wherein the short codeword decoding acceleration unit is configured to, when the codeword to be decoded is a short codeword, according to the variable-length code encoding rule Obtaining the order of the Exponential Golomb code corresponding to the numerical value of the input code segment. the

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