BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS
Other objects, features and advantages will occur to those skilled in the art from the following description of a preferred embodiment and the accompanying drawings, in which:
FIG. 1 is flow block diagram of a prior art method of performing H.264 CABAC decoding with unknown probabilities for MPS/LPS:
FIG. 2 is flow block diagram of a method of performing CABAC decoding with rotated architecture according to this invention;
FIG. 3 is a more generalized flow block diagram of the method with rotated architecture according to this invention;
FIG. 4 is a more detailed flow block diagram of the prior art method of CABAC decoding of FIG. 1;
FIG. 5 is a more detailed flow block diagram of the method of CABAC decoding of FIG. 2 according to this invention;
FIG. 6 is a more detailed flow block diagram of a parallel process for generating the new context next rLPS concurrently with the next rLPS;
FIG. 7 is a directory of FIGS. 7A and 7B which are schematic block diagram of an arithmetic processor with four compute units for implementing this invention;
FIG. 8 is a flow block diagram of a prior art method of performing CABAC decoding with equal probabilities for MPS/LPS; and
FIG. 9 is a flow block diagram of a method of performing CABAC decoding with equal probabilities for MPS/LPS using rotated architecture according to this invention.
DETAILED DESCRIPTION OF THE INVENTION
Aside from the preferred embodiment or embodiments disclosed below, this invention is capable of other embodiments and of being practiced or being carried out in various ways. Thus, it is to be understood that the invention is not limited in its application to the details of construction and the arrangements of components set forth in the following description or illustrated in the drawings. If only one embodiment is described herein, the claims hereof are not to be limited to that embodiment. Moreover, the claims hereof are not to be read restrictively unless there is clear and convincing evidence manifesting a certain exclusion, restriction, or disclaimer.
There is shown in FIG. 1 a routine or process 8 of CABAC decoding such as in H.264. A first or antecedent function 10 responds to present range 12, value 14, and context [State,MPS]16 to calculate rLPS and intermediate range˜. First or antecedent function 10 then provides the intermediate range˜18, rLPS 20, the present value 14, and context 16 to the second or subsequent function 22. Function 22 generates the next range, range′, the next value, value′, and the next context, context′. One problem with this prior art implementation is that before the second or subsequent function 22 can be run, intermediate range ˜18 and rLPS 20 have to be calculated by the first or antecedent function 10. In pipelined machines this means that function 22 is dependent on function 10 and subject to pipeline stall, delays. This is so because for each time, before function 22 can execute, it must wait on function 10 performing the necessary operations to generate intermediate ranged ˜18 and rLPS 20.
In accordance with this invention, routine or process 30, FIG. 2, rotates or advances the iterative process or routine by preliminarily providing to the subsequent function the one or more parameters on which is it dependent and then generating by the subsequent function in response to those parameters one or more parameters required by the antecedent functions and then generating via the one or more antecedent functions in response to its required parameters, one or more parameters input to the subsequent function for the next iteration. Thus, the iterative process is rotated by preliminarily 32 generating the next rLPS, rLPS′ at 34 from the present range 36, context 38, and value 40. This next rLPS′ 34 becomes the present rLPS 42 as provided in conjunction with the present range 44, value 46 and context 48 to the second or subsequent function 50 resolving in function 50 the dependency of current range on the two dimensional state/range look-up table of rLPS. From this, subsequent function 50 generates the next value′ 52, updated next range′ 54 and updated next context′ 56. Then the first or antecedent function 58 calculates the next iteration rLPS′ from the next range′ and next context′ thereby resolving the dependency of next iteration range on the 2D look-up table of rLPS. The rotation of the architecture has been effected by generating with the antecedent function at the end of this iteration, the inputs needed by the subsequent function in the next iteration. The output of first or antecedent function 58 is then next range′ 54, next value′ 52, next context′ 56 and the next iteration rLPS′ 34 so that the dependency on the 2D LUT of rLPS of the evaluation of the intimidate range˜ of the next iteration of function 50 is resolved.
In terms of the CABAC implementation of this specific embodiment the first or antecedent function 58 is the range subdivision function and the second or subsequent function 50 is the CABAC parameter update.
While FIG. 2 is explained with regard to a CABAC decoding application, this is only one embodiment of the invention. This invention is applicable to e.g. H.264 CABAC encoding/decoding as well as arithmetic coding in JPEG2000, JPEG, On2 and many other encoding and decoding applications. Even more generally the invention contemplates that for any process 60, FIG. 3, having an antecedent or first function 62 and a subsequent or second function 64, the process operation or architecture can be rotated so that initially, preliminarily 66 one or more parameters on which the subsequent function depends are generated and delivered directly to the subsequent function 64 which then generates one or more parameters 70 on which the antecedent function depends. Antecedent function 62 then determines the one or more parameters 68 on which the subsequent function depends for the next iteration. In this way at the end of each iteration the necessary parameters for the subsequent function are already generated and await only new inputs that don't have to be determined.
Prior art CABAC process 8a, FIG. 4, receives three inputs, present range 80, value 82, and context 84. In the first step 86, rLPS and intermediate range˜ are calculated. rLPS is typically generated using a look-up table in an associated compute unit. In step 88 it is determined as to whether value is greater than the intermediate range˜. If it is not greater than the intermediate range˜, the Most probable symbol path is taken where in step 90 MPS is assigned as the output bit and the state of the context is updated using a second look-up table (the MPS-transition table). If the value is greater that the range the Least probable symbol path is taken where in step 92 an inverted MPS is assigned as the output bit, the next value is calculated from the value and the intermediate range˜ and the next range is determined from the rLPS. Following this in step 94, if the state is equal to zero the MPS is negated in step 96. If state is not equal to zero following step 94, or following step 96, a new state is determined 98 from a third look-up table (the LPS-transition table). Finally, whether the value is greater than or less than the range, the respective outputs are renormalized 100 to a range between 256 and 512, the Value is scaled up accordingly and the new LSB bits of Value are appended from the bit stream FIFO. The outputs resulting then are the normalized next range, range′, normalized next value, value′, and next context, context′. The operation of process 8a is effected by arithmetic encoder/decoder 135. The first portion is the first or antecedent function 10, FIG. 1, implementing the CABAC range subdivision function 137, FIG. 4, the second portion is the second or subsequent function 22, FIG. 1, implementing the CABAC parameter update function 139. As can be seen at 137 the evaluation of range˜ must stall until the two dimensional state/range look-up table of rLPS result is resolved.
In contrast CABAC decoder processor 30a in accordance with this invention, FIG. 5, has four inputs, present range, 102, present rLPS 104, present value 106, and present context 108. In the process 30a according to this invention the present rLPS 104 is supplied either externally as in step 32 in FIG. 2 initially, and then once the operation is running, by the preliminary generation of the next rLPS′ by the antecedent or first function 58, FIG. 2. With the rLPS being supplied preliminarily in either case the dependency of range˜ on the two dimensional state/range look-up table of rLPS result is resolved, and the intermediate range˜ is determined from the present range and the present rLPS in step 110. Then in step 112 it is determined whether the value is greater than the intermediate range, if it is not, once again the Most probable symbol path is taken where in step 114 the MPS is assigned to a bit and the state of the context is updated by reference to a first MPS-transition look-up table. If the value is greater than the intermediate range then the Least probable symbol path is taken where MPS has assigned to it the inverted bit, next value′ is determined from present value and intermediate range˜ and the next range′ is determined from the rLPS. In step 118 inquiry is made as to whether the state is equal to zero. If it is the MPS is negated in step 120. In step 122 the new context state is determined from a second LPS-transition look-up table. In either case in step 124 the system is renormalized as previously explained. Then the first or antecedent function 126 occurs: that is the first two operations in step 86 of the prior art device, FIG. 4, are now performed after the subsequent functions. There in step 126 the next rLPS, rLPS′ is determined from the range/state using a third 2D look-up table. The output then is the next range, range′ 128 the next rLPS, rLPS′ 130, the next value, value′ 132, and the next context, context′ 134. The operation of process 30a is effected by arithmetic decoder 135a. The first portion is the second or subsequent function 50, FIG. 2, implementing the CABAC parameter update function 139a; the second portion is the first or antecedent function 58, FIG. 2, implementing the CABAC range subdivision function 137a.
Note that the next rLPS′, which is anticipatorily generated in the methods of this invention shown in FIGS. 2 and 5, is based on a particular context value. As long as this context is going to be used in the next iteration the anticipatory next rLPS, rLPS′ being calculated in advance is proper. However, occasionally context itself may change in which case a new context next rLPS′ or, rLPS″ will have to be created for the new context. This is accommodated by an additional routine or process 140, FIG. 6, which may operate in parallel with the method or process 30a, FIG. 5. In FIG. 6, the present range 142, rLPS 144, value 146, and new context 148, are provided and process 140 generates the new context next rLPS, rLPS″ 150 so that even though the rLPS′ 130, FIG. 5, generated from the old context 108 is improper the new context next rLPS″ 150 will be ready for the preliminary use. Only one of rLPS′ and rLPS″ will be chosen to be used; the other will be abandoned.
Process 30a, FIG. 5, may be implemented in a pair of compute units 160, 162, FIGS. 7A and 7B, each including a variety of components including e.g., multiplier 164, polynomial multiplier 166, look-up table 168, arithmetic logic unit 170, barrel shifter 172, accumulator 174, mux 176, byte ALUs 178. Compute units 160, 162 perform the method or process 30a of FIG. 5, and look-up tables 168, 168a fill the role of the necessary look-up tables in steps 114, 122, and 126 referred to in FIG. 5. A second set of compute units 160′, 162′ having the same components can be used operating in parallel on the same inputs range 102, rLPS 104, value 106, and context 108 where the context can be a new context to provide at the output a new context next rLPS, rLPS″ 180. Compute units 160, 160′ 162, 162′ are accessed through registers 161 and 163.
While thus far the explanation has been with respect to situation where the probability between the LPS and MPS is not known, there are cases where the probability of LPS to MPS is equal e.g. 50%. In that case the first or antecedent function 200, FIG. 8, responds to value 202, and range 204 to provide next value′ 206 and the second or subsequent function 208 responds to the next value′ 206, to determine the output bit and range to provide the output bit 210 and the next value′ 206 output. Again here the second or subsequent function 208 is dependent on the completion of the first or antecedent function 200 and in a pipelined machine that dependency can result in delays due to pipeline stall because the next value, value′ required by second or subsequent function 208 must be determined in the first or antecedent function 200 using the inputs of present value 202 and range 204.
In accordance with this invention once again the architecture can be rotated so that initially, preliminarily, FIG. 9, the next value′ 220 can be determined from the present value 222 in step 224. Then with the next value, value′ 220 presented as the present value 226 along with range 228, the second or subsequent function 230 can execute immediately to determine the next bit 230. Then the first or antecedent function 234 can pass through the bit 232 and calculate the next value, value′ and have it ready preliminarily for the next iteration 234 where it will appear as the present value at 226.
Although specific features of the invention are shown in some drawings and not in others, this is for convenience only as each feature may be combined with any or all of the other features in accordance with the invention. The words “including”, “comprising”, “having”, and “with” as used herein are to be interpreted broadly and comprehensively and are not limited to any physical interconnection. Moreover, any embodiments disclosed in the subject application are not to be taken as the only possible embodiments.
In addition, any amendment presented during the prosecution of the patent application for this patent is not a disclaimer of any claim element presented in the application as filed: those skilled in the art cannot reasonably be expected to draft a claim that would literally encompass all possible equivalents, many equivalents will be unforeseeable at the time of the amendment and are beyond a fair interpretation of what is to be surrendered (if anything), the rationale underlying the amendment may bear no more than a tangential relation to many equivalents, and/or there are many other reasons the applicant can not be expected to describe certain insubstantial substitutes for any claim element amended.
Other embodiments will occur to those skilled in the art and are within the following claims.
Patent Application
20080075376
