Engine::cross is the one place a dot product is computed during
agglomeration — when two groups become adjacent through a third and
their sub-threshold pairs, never summed because they were never
interesting, have to be accounted for. It was calling the portable loop
while the scan beside it had AVX2 or NEON, which on the reference
library was 1,753,514 dot products taking 0.54s.
Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
dtourolleandClaude Opus 5
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