Variable length coder with a small table size
AssigneeMatsushita Electric Industrial Co., Ltd.
InventorWilliam Brent Wilson
Life of this patent
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Abstract
The invention described herein is a versatile variable length coder with a small table side. The size of the table was reduced by the use of a linked list of groups of like valued run-level code words for the code table, the effect of which is the ability to store and access the Huffman code words without reserving space for the holes in the Huffman tables. Traversing the linked list as the fixed length codes are input has the effect of eliminating the requirement that sequences of codes are run-level fixed length coded before being variable length coded. This simplifies encoder architectures and circuits. The result is the dramatic reduction in size of a programmable variable length coder, making them suitable for implementation in VLSI implementations of digital audio and video codecs.
Claims12
A circuit arrangement for a variable length coder for converting a stream of fixed bit length codes to a stream of variable bit length codes comprising:
- a fixed length code stream input for inputting sequences of fixed length codes;
- a variable length code stream output for outputting sequences of variable length codes;
- a code table for storing code words, said code words means for defining the bit sequence and length of said bit sequence of said variable length codes;
- an address generator for calculating the code table address, said code table address used to index said code table;
- an escape coder for calculating escape codes, said escape codes means for defining said variable length codes corresponding to sequences of fixed length codes which do not have an entry in said code table;
- an escape selector for selecting said escape codes or said code words to be said variable length codes which are the output of said variable length coder;
- an escape code decider for deciding if said fixed length codes have an entry in said code table;
- a code valid decider for deciding if said sequence of fixed length codes have a corresponding variable length code.
Dependencies are inferred from the claim text.