perf: branchless boolean zip kernel#8275
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Add a dedicated `ZipKernel for Bool` that blends the two value bitmaps with the mask in a single bitwise pass -- `(true & mask) | (false & !mask)` -- instead of the generic per-run builder, so boolean zips are branch-free and mask-shape independent. Also add a shared `zip_validity` helper to the zip module that builds the result validity as a (lazy) zip over the two boolean validity bitmaps, reusing this kernel. This gives the per-encoding zip kernels one shared validity-selection path; the recursion terminates immediately because validity bitmaps are non-nullable. Adds a small `bool_zip` divan benchmark (nonnull ~7us, nullable ~14us). Signed-off-by: Joe Isaacs <joe.isaacs@live.co.uk>
joseph-isaacs
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Claude
The doc comment on the public ZipKernel impl linked to the pub(crate) zip_validity, which -D rustdoc::private-intra-doc-links rejects. Use a plain code span instead. Signed-off-by: Joe Isaacs <joe.isaacs@live.co.uk>
Merging this PR will not alter performance
|
| Mode | Benchmark | BASE |
HEAD |
Efficiency | |
|---|---|---|---|---|---|
| ❌ | Simulation | chunked_varbinview_canonical_into[(100, 100)] |
274.5 µs | 309.3 µs | -11.27% |
| ⚡ | Simulation | chunked_varbinview_canonical_into[(1000, 10)] |
198.1 µs | 161.6 µs | +22.57% |
| ⚡ | Simulation | encode_varbin[(1000, 8)] |
165.2 µs | 145.3 µs | +13.69% |
| ⚡ | Simulation | encode_varbin[(1000, 4)] |
164.1 µs | 144.6 µs | +13.48% |
| ⚡ | Simulation | encode_varbin[(1000, 32)] |
170.4 µs | 150.6 µs | +13.16% |
| 🆕 | Simulation | nonnull |
N/A | 54.5 µs | N/A |
| 🆕 | Simulation | nullable |
N/A | 93.7 µs | N/A |
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Comparing claude/bool-branchless-zip (86f2413) with develop (42640f5)
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## Summary Adds a dedicated primitive zip kernel that selects values branchlessly per row. The generic zip path copies runs of `if_true`/`if_false` between mask boundaries — fast for clustered masks but degrading to per-element work on fragmented masks. This kernel walks the mask as 64-bit chunks and blends both sides per row with no data-dependent branch, so the inner loop stays branch-free and auto-vectorizable regardless of mask shape. Result validity reuses the shared `zip_validity` helper, which expresses validity selection as a (lazy) zip over the two validity bitmaps. > The branchless boolean zip kernel (#8275) this builds on has now merged into `develop`; this branch has been rebased on top of it, so the diff here is primitive-only.
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Summary
Adds a dedicated, branchless
ZipKernel for Bool.