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Update FEXPA instruction details and implementation steps
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content/learning-paths/servers-and-cloud-computing/fexpa/fexpa.md

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---
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title: FEXPA
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title: Optimize with FEXPA instruction
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### FIXED, DO NOT MODIFY
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## The FEXPA instruction
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Arm introduced in SVE an instruction called FEXPA: the Floating Point Exponential Accelerator.
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Arm introduced an instruction in SVE called FEXPA: the Floating Point Exponential Accelerator.
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Let’s segment the IEEE 754 floating-point representation fraction part into several sub-fields (Index, Exp and Remaining bits) with respective length of _Idxb_, _Expb_ and _Remb_ bits.
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The IEEE 754 floating-point representation fraction part can be segmented into several sub-fields (Index, Exp and Remaining bits) with respective length of _Idxb_, _Expb_ and _Remb_ bits.
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| IEEE 754 precision | Idxb | Expb | Remb |
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|-------------------------|------|------|------|
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## Exponential implementation with FEXPA
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FEXPA can be used to rapidly perform the table lookup. With this instruction a degree-2 polynomial is sufficient to obtain the same accuracy as the degree-4 polynomial implementation from the previous section.
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Use FEXPA to rapidly perform the table lookup. With this instruction, a degree-2 polynomial is sufficient to obtain the same accuracy as the degree-4 polynomial implementation from the previous section.
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### Add the FEXPA implementation
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```
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{{% notice Arm Optimized Routines %}}
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This implementation can be found in [ARM Optimized Routines](https://github.com/ARM-software/optimized-routines/blob/ba35b32/math/aarch64/sve/sv_expf_inline.h).
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This implementation can be found in [Arm Optimized Routines](https://github.com/ARM-software/optimized-routines/blob/ba35b32/math/aarch64/sve/sv_expf_inline.h).
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{{% /notice %}}
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The benchmark shows the performance progression:
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1. **SVE with degree-4 polynomial**: Provides up to 4x speedup through vectorization
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2. **SVE with FEXPA and degree-2 polynomial**: Achieves an additional 1-2x improvement
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- SVE with degree-4 polynomial provides up to 4x speedup through vectorization
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- SVE with FEXPA and degree-2 polynomial achieves an additional 1-2x improvement
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The FEXPA instruction delivers this improvement by:
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- Replacing manual bit manipulation with a single hardware instruction (`svexpa()`)
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- Enabling a simpler polynomial (degree-2 instead of degree-4) while maintaining accuracy
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Both SVE implementations maintain comparable accuracy (errors in the 10^-9 to 10^-10 range), demonstrating that specialized hardware instructions can significantly improve performance without sacrificing precision.
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## What you've accomplished and what's next
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In this section, you:
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- Implemented exponential function optimization using the FEXPA instruction
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- Reduced polynomial degree from four to two while maintaining accuracy
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- Achieved up to 6x speedup over the baseline implementation
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Next, you'll review the key benefits and applications of FEXPA optimization.

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