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neonsoftmax

confirmedC++ · NEON / Apple M4Systems & data structuresJuly 6, 2026

the question

How much does a hand-written NEON softmax over the vocabulary beat scalar libm, and at what accuracy cost?

what came out

More than 2x the scalar throughput across vocab sizes (32k-152k), at negligible cost -- relative-L2 under 1e-4 from the polynomial exp -- and consistent across vocabulary size. Standalone C++ ARM NEON; all three pre-registered predictions held.

method & receipts

  • Result: confirmed
  • Pre-registered the prediction was written down and committed before the run.
  • Reproducible one script re-runs the whole thing from scratch.
  • Independently reviewed an adversarial review pass, kept in the repo.
  • Machine-readable claims every reported number, in a checkable file.
  • Tested — a correctness/benchmark suite ships alongside the code.

→ read the code and re-run it

github.com/v-code01/neonsoftmax