Variable-Length Instruction Encoding Using Predicted Word Suppression
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Solution Overview
Problem
Existing methods for encoding and decoding instructions from an instruction set face challenges in achieving high code density and flexibility, particularly when using variable length instruction words, which can increase hardware complexity and make it difficult to add new instructions without reducing code density and efficiency.
Innovation Solution
The method involves re-ordering and grouping bits in instructions into variable-length instruction words based on empirical or simulation data, omitting words that match predicted values to create a compressed version, allowing for different instructions to use different numbers of words, and using a mask to selectively omit words, thereby improving code density and flexibility.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If variable length instruction words are used to increase code density, then code density is improved, but hardware complexity increases
Solution Approach 1:
The instruction is divided into multiple fixed-size words (e.g., 32-bit words) that are processed sequentially. Each word contains a portion of the instruction bits, allowing the decoder to handle complex instructions through multiple simpler word units rather than requiring complex variable-length encoding logic.
Solution Approach 2:
The instruction bits are pre-ordered and grouped into fixed-size words before decoding. This preliminary organization allows the decoder to use simple fixed-width word processing logic while still achieving variable-length instruction encoding, as the variable-length semantics are established in advance through the bit ordering and grouping process.
2Quantity of substance
If variable length instruction words are used to improve code density, then code density is improved, but difficulty in adding new instructions increases
Solution Approach 1:
By segmenting the instruction into fixed-size words with consistent internal structure, new instructions can be added by defining new bit patterns within the established word format without requiring changes to the fundamental encoding architecture or variable-length handling logic.
Solution Approach 2:
The invention changes the parameter of instruction representation from variable-length words to fixed-length words with variable content. This allows the instruction set to be extended by varying the semantic interpretation of bit fields within the fixed words rather than requiring new word lengths, thereby improving adaptability.
3Quantity of substance
If shorter instruction words are used to increase code density, then code density is improved, but functionality of the instruction set is limited
Solution Approach 1:
The instruction is segmented into multiple fixed-size words that are processed in sequence. This segmentation allows the full functionality to be distributed across multiple words rather than requiring each word to contain all possible operational codes, thereby maintaining full instruction set functionality while achieving compact encoding.
Solution Approach 2:
The invention transitions from a single-dimension variable-length word approach to a multi-dimensional approach where instructions are represented as sequences of fixed-size words. This dimensional change allows the system to achieve code density through sequence optimization while maintaining full functionality through the extended word sequence structure.
Data Source
AI summary
Methods of encoding and decoding are described which use a variable number of instruction words to encode instructions from an instruction set, such that different instructions within the instruction set may be encoded using different numbers of instruction words. To encode an instruction, the bits within the instruction are reordered and formed into instruction words based upon their variance as determined using empirical or simulation data. The bits in the instruction words are compared to corresponding predicted values and some or all of the instruction words that match the predicted values are omitted from the encoded instruction.