Skip dense meet joined-mask scans#47
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Implements the TODO in the dense meet: instead of walking both dense nodes' full masks and re-testing membership per byte, walk the intersection mask directly, so bytes absent from either side are never visited. No public API change; is_identity handling is equivalent (the intersection walk observes the same element/identity outcomes the full walk did). Motivated by the existing meet benchmarks, measured on this tree vs its base (interleaved, two reps each side, best median): superdense_meet 8000 26.1->25.0us, 16000 42.5->39.8us, 32000 100->93.9us (a consistent 4-6% where the masks are dense); sparse_meet and binary_meet at parity to -2% (their masks are thin, so there is little scan to skip). Result-identical: the full suite and the seeded algebra differential pass, including composed with the DenseByteNode operand-selection fix (both touch this file; they auto-merge and the differential passes with both applied).
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Summary
Implements the TODO in the dense meet: instead of walking both dense nodes'
full masks and re-testing membership per byte, walk the intersection mask
directly, so bytes absent from either side are never visited. No public API
change;
is_identityhandling is equivalent (the intersection walk observesthe same element/identity outcomes the full walk did).
Result
Measured on this branch vs
master(interleaved, two reps each side, bestmedian):
superdense_meet8000 26.1→25.0us, 16000 42.5→39.8us, 32000100→93.9us (a consistent 4-6% where the masks are dense);
sparse_meetandbinary_meetat parity to -2% (their masks are thin, so there's little scanto skip). Composes cleanly with
pr/pathmap-hardening's DenseByteNodeoperand-selection fix (both touch this file; they auto-merge, and the
algebra differential passes with both applied).
Test plan
cargo test --release --lib(660/0, matches themasterbaseline)cargo test --release --test pathmap_algebra_differential(4/4)cargo bench --bench superdense_keys / sparse_keys / binary_keys -- meet