Processor Circuitry for Fused Multiply-Add with Denormal Numbers
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Solution Overview
Problem
Existing processor architectures lack the capability to efficiently perform fused multiply-add operations with denormal numbers, requiring microcode assistance that introduces multi-cycle delays and degrades performance.
Innovation Solution
The implementation of a processor circuitry that supports fused multiply-add operations on denormal numbers without microcode assistance, utilizing techniques such as one-way alignment, radix-16 Booth encoding, merged J-bit correction, modified leading zero anticipation, parallel sticky and all-ones detection, and merged two's complement rounding logic, allowing for full denormal support in 4 cycles.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If microcode assistance is used to handle denormal numbers, then denormal number processing capability is provided, but multi-cycle delay occurs and performance degrades
Solution Approach 1:
The patent replaces the microcode-based exception handling mechanism with a dedicated hardware circuit (denormal number handling circuit) that can directly process denormal numbers. This substitution of mechanical/software control with specialized hardware eliminates the multi-cycle delay associated with microcode execution while maintaining full denormal number processing capability.
Solution Approach 2:
The patent introduces an intermediary denormal number handling circuit between the floating-point unit and the output stage. This intermediary circuit detects denormal results and processes them in parallel with the main execution pipeline, allowing the system to handle denormal numbers without stalling the pipeline or invoking microcode, thus avoiding performance degradation.
2Speed
If traditional floating-point units only deal with normal numbers, then processing speed is maintained, but denormal number handling requires microcode exception handler
Solution Approach 1:
The patent designs a floating-point unit that can universally handle both normal and denormal numbers through integrated hardware support. The denormal number handling circuit works in conjunction with the main floating-point unit to provide multi-functionality, allowing the same hardware to process all floating-point numbers regardless of their normalization state, eliminating the need for separate microcode exception handling.
Solution Approach 2:
The patent performs preliminary detection and handling of denormal numbers during the main execution pipeline rather than as a post-processing exception. The denormal number handling circuit operates in parallel with the primary computation, identifying and processing denormal results before they would otherwise require microcode intervention, thus maintaining processing speed while reducing complexity.
3Adaptability or versatility
If microcode exception handler is used to compute denormal numbers, then denormal computation is achieved, but cycles of additional delay occur
Solution Approach 1:
The patent maintains continuous processing throughput by implementing the denormal number handling circuit that operates in parallel with the main execution pipeline. This allows useful computation to continue without interruption or stalls that would otherwise occur when invoking a microcode exception handler, ensuring that productivity is maintained while achieving full denormal computation capability.
Solution Approach 2:
The patent substitutes the sequential microcode exception handling mechanism with a parallel hardware-based denormal processing circuit. This mechanical substitution enables denormal computation to occur concurrently with normal operations rather than requiring sequential exception handling, thereby maintaining high processing throughput while achieving complete denormal number support.
Data Source
AI summary
Techniques and mechanisms for circuitry to support the performance of a fused multiply-add (FMA) operation with one or more denormal numbers. In some embodiments, a processor is operable to execute a FMA instruction comprising or otherwise identifying two multiplicands, and an addend. Such execution includes performing one-way alignment of an addend significand based on a difference between respective exponent values of the two multiplicands. The alignment is performed in parallel with operations by a multiplier circuit based on respective significand values of the two multiplicands. Subtraction of a J-bit correction value is performed in the multiplier circuit to avoid mitigate execution delay. In another embodiment, first circuitry of a processor executes an FMA instruction, wherein components of the first circuitry are shared with second circuitry of the processor, and wherein the second circuitry supports the execution of a floating-point multiplication instruction.