Method and system for predictive table look-up code length of variable length code
View Patent ↗A method and system for decoding symbols of variable length in a digital video bit stream in real time, using Very Long Instruction Word (VLIW) architecture. In one embodiment, several bit sections are first read from a bit stream. While the first bit section will correspond to a valid symbol in the bit-stream, the rest of the bit sections may or may not, depending on the length of the first section. A table of variable length codes is then indexed to obtain a look-up result for each of the read-in bit sections, which done in parallel for all sections. Next, a determination is made as to whether each of the look-up results is valid. A valid look-up result provides the length of the symbol. The valid look-up values are then accepted. In another embodiment the bit stream is thereafter advanced by the sum of all accepted look-up results.
1. A method of processing a signal comprising:
a) reading a first bit section from a bit stream of variable length codes beginning at a reference bit of said bit stream, wherein said reading a first bit section is performed in a given direction;
b) reading a second bit section from said bit stream beginning at a first offset from said reference bit of said bit stream, wherein said reading a second bit section is performed in said given direction, wherein steps a) and b) are done in parallel, and wherein said first offset is less than a minimum symbol length;
c) indexing a table with said first bit section to obtain a first look-up result, said table comprising a plurality of variable length codes and a corresponding plurality of code lengths, said first look-up result describing the length of a first symbol in said bit stream;
d) indexing said table with said second bit section to obtain a second look-up result, wherein steps c) and d) are done in parallel;
e) determining if said second look-up result from step d) is valid; and
f) accepting said second look-up result if it is valid, wherein said second look-up result describes a second symbol length in said bit stream.
2. The method of claim 1 further comprising:
g) advancing the reference bit of said bit stream by the sum of said first and second symbol lengths; and
h) repeating steps a) through f).
3. The method of claim 1 further comprising:
g) reading a third bit section from said bit stream beginning at a second offset from said reference bit of said bit stream, wherein step a), step b), and step g) are done in parallel;
h) indexing said table with said third bit section to obtain a third look-up result, wherein step c), step d), and step h) are done in parallel; and
i) determining whether said third look-up result from step h) is valid.
4. The method of claim 3 wherein said second offset is one bit greater than said first offset.
5. The method of claim 1 , wherein said first offset is equal to the minimum code length of codes in said table.
6. The method of claim 1 wherein said bit stream comprises digital video data.
7. The method of claim 1 wherein said bit stream comprises data in MPEG format.
8. The method of claim 1 wherein said bit stream comprises data encoded with Huffman coding.
9. A system for processing a signal comprising:
means for reading a first bit section from a bit stream of variable length codes beginning at a reference bit of said bit stream, wherein said reading a first bit section is performed in a given direction;
means for reading a second bit section from said bit stream beginning at a first offset from said reference bit of said bit stream, wherein said reading a second bit section is performed in said given direction, wherein said reading said first bit section and said reading said second bit section are done in parallel, and wherein said first offset is less than a minimum symbol length;
means for indexing a table with said first bit section to obtain a first look-up result, said table comprising a plurality of variable length codes and a corresponding plurality of code lengths, said first look-up result describing the length of a first symbol in said bit stream;
means for indexing said table with said second bit section to obtain a second look-up result, wherein said indexing a table with said first bit section and said indexing a table with said second bit section are done in parallel;
means for determining if said second look-up result is valid; and
means for accepting said second look-up result if it is valid, wherein said second look-up result describes a second symbol length in said bit stream.
10. The system of claim 9 further comprising:
means for advancing the reference bit of said bit stream by the sum of said first and second symbol lengths.
11. The system of claim 9 further comprising:
means for reading a third bit section from said bit stream beginning at a second offset from said reference bit of said bit stream, wherein said reading a third bit section is done in parallel with said reading said first bit section and said reading said second bit section;
means for indexing said table with said third bit section to obtain a third look-up result, wherein said indexing a table with said third bit section is done in parallel with said indexing a table with said first bit section and said indexing a table with said second bit section; and
means for determining whether said third look-up result is valid.
12. The system of claim 11 wherein said second offset is one bit greater than said first offset.
13. The system of claim 9 , wherein said first offset is equal to the minimum code length of codes in said table.
14. The system of claim 9 wherein said bit stream comprises digital video data.
15. The system of claim 9 wherein said bit stream comprises data in MPEG format.
16. The system of claim 9 wherein said bit stream comprises data encoded with Huffman coding.