Pattern Matching Outperformed Hand-Written SIMD

Wed, 15 Apr 2026 10:04:00 -0700

Our base64 decoder was implemented twice. Version 1 used explicit cross-lane operations — shuffles, rotations, compact stores. It peaked at roughly 2x scalar performance. Version 2 used four plain go for loops with no cross-lane operations at all. It hit approximately 17 GB/s on AVX2 — about 77% of simdutf C++ and 9x faster than Go’s encoding/base64. The simpler code outperformed the clever code by a wide margin.

Pattern-Detection on Cedric Bail

Pattern Matching Outperformed Hand-Written SIMD