Data processing apparatus
A programmable data processing apparatus having a bit-plane extraction operation is described, for extracting data from a value of, for example, 32 bits containing 4 bytes, 1 a to 1 d . Each byte 1 a to 1 d comprises 8 bits, (a 0 -a 7 , b 0 -b 7 , c 0 -c 7 and d 0 -d 7 , respectively). The bit-plane extraction operation retrieves one bit from each of these bytes, for example the second bit (a 1 , b 1 , c 1 , d 1 ), which is specified by an argument. The operation involves concatenating these bits (a 1 , b 1 , c 1 , d 1 ) and returning a result value 5 . Depending on the particular data processing application, the result value may be bit-reversed to provide a result value 7 (for example, if a bit-reversal is required to deal with endianness, or other reasons). The bit-plane extraction operation can be used as a pre-processing operation in data processing operations such as “sum-of-absolute-differences” in the processing of video data.
1. A programmable data processing apparatus for processing data, the data processing including the task of performing a bit-plane extraction operation on packed data bits, the packed data bits comprising a plurality of data elements, each data element having a plurality of data bits, the apparatus comprising:
extracting means for selectively extracting a data bit from each of the data elements, the extracting means comprising a plurality of multiplexers, the plurality of multiplexers being arranged to select a particular data bit from each data element and the multiplexers being configured in a plurality of levels, each level selectively reducing the number of bits in each data element from n to n/2, until a desired bit is selected, and
concatenating means for concatenating the extracted data bits to provide a result value, wherein the result value is further processed by the programmable data processing apparatus.
2. The apparatus of claim 1 , wherein the extracting means is adapted to select more than one data bit from each of the data elements.
3. The apparatus of claim 1 , wherein each data element comprises a data byte, and wherein the apparatus is configured to extract a predetermined data bit or bits from each of the plurality of data bytes.
4. The apparatus of claim 1 , further comprising bit-reversing means for reversing the order of the data bits in the result value prior to subsequent processing by the programmable data processing apparatus.
5. The apparatus of claim 4 , wherein the bit-reversing means for reversing the bit order comprises a series of multiplexers, the multiplexers being arranged such that:
in a first mode of operation the concatenated data bits forming the result value pass through the multiplexers without changing the order of the result value; and
in a second mode of operation the order of the concatenated data bits is reversed while passing through the multiplexers.
6. The apparatus of claim 5 , wherein the mode of operation is controlled by a parameter, thereby enabling the bit-reversal means to be dynamically controlled depending on a particular data processing application.
7. The apparatus of claim 1 , the apparatus further comprising means for combining the result value with a previous result value.