Parallel Prefix-Code Decoding with Leftover Bit Propagation
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Solution Overview
Problem
Decoding variable-length prefix codes is difficult to parallelize due to unknown boundaries between code words, limiting hardware efficiency and throughput in existing decoding processes.
Innovation Solution
The method involves preprocessing a stream of prefix code words into fixed-width chunks, using parallel decoder circuits and subsequent stages of leftover bit propagation to enable pipelined decoding, reducing dependence paths and allowing parallelization across inputs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If variable-length prefix codes are decoded using traditional sequential methods, then decoding accuracy is maintained, but throughput is limited and hardware efficiency is reduced
Solution Approach 1:
The input bit stream is segmented into fixed-length words, where each word contains a portion of one or more encoded symbols. This segmentation enables parallel processing of multiple words simultaneously through multiple decoder circuits, thereby increasing throughput while maintaining manageable complexity through modular architecture
Solution Approach 2:
The patent transitions from sequential one-dimensional processing to parallel multi-dimensional processing by introducing multiple decoder circuits that operate simultaneously on different fixed-length words. Multiple sets of decoder circuits process different portions of the bit stream in parallel, effectively adding a temporal parallelism dimension to the decoding process
2Speed
If parallel decoder circuits are used to increase throughput, then decoding speed improves, but handling variable-length boundaries becomes difficult
Solution Approach 1:
The bit stream is pre-processed into fixed-length words before parallel decoding begins. This preliminary action establishes uniform processing units that can be handled by parallel decoder circuits without requiring dynamic boundary detection during the decoding process itself, thereby enabling high-speed parallel operation
Solution Approach 2:
Fixed-length words serve as intermediaries between the variable-length prefix code stream and the parallel decoder circuits. These intermediary structures provide a uniform interface that masks the underlying variable-length nature of the codes, allowing parallel decoders to operate efficiently without directly confronting boundary detection complexity
3Productivity
If fixed-length words are used for parallel processing, then hardware efficiency increases, but precise symbol boundaries may be lost
Solution Approach 1:
The system employs feedback mechanisms where decoder circuits exchange information about their processing state and results. This feedback enables the system to track and reconstruct symbol boundaries across the fixed-length word boundaries, ensuring that no information is lost despite the fixed-length segmentation used for parallel processing
Data Source
AI summary
Methods and systems are provided for decoding variable-length codes in a parallel process. A stream of variable-length code words is divided into fixed length words. A plurality of parallel sets of decoder circuits each receive, in parallel, a current fixed length word and a prior fixed length word. Each decoder circuit has a respective fixed leftover bit-count. Each decoder circuit generates a respective output that may include a decoded symbol and a new leftover bit-count. Each respective output is determined based on the respective current fixed length word, the respective prior fixed length word, and the respective fixed leftover bit-count. A set of selected decoder circuit outputs is generated for each set of the parallel sets of decoder circuits based on a set of first leftover bit-counts. One output from each set of selected decoder circuit outputs is selected as a final output based on a second prior leftover bit-count.