simd: data-indexed mask primitives — gather, scatter-or, keyed group-sum, indexed predicate, key-run distinct fold - #318
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…group-sum `mask_gather_u32(src, src_rows, index, out)`: bit i of out = src[index[i]], an out-of-range address reads FALSE (zero-fallback). The foreign-key semijoin: a predicate mask over table B gathered onto table A through A's fk lane, no index vector, no pair relation. `mask_scatter_or_u32(src, index, out, out_rows)`: for every set bit i of src, set bit index[i] of out. The one-to-many hop (docs that have a selected line). Cost ∝ popcount(src). `masked_group_sum_i32(mask, keys, values, out)`: out[keys[i]] += values[i] over the mask, ONE pass, all groups; a key past out.len() is not a group. This is the terminal a categorical GROUP BY … SUM lowers to — and it is NOT `masked_strided_group_sum`, which sums the byte-groups of one V3 register into one scalar, carries no key, and has zero callers. All three are deliberately scalar bit-walks: data-indexed permutations and scatter-adds do not vector-load, the same reasoning `masked_strided_group_sum` already records. 26 unit tests (tails at 67/130, out-of-range dropped, garbage-prefilled buffers come back tail-zero), parity check group 13 against naive references with out-of-range addresses mixed in, gather's range guard disable-verified red (2 tests + parity 0xD00) then green. Consumer: lance-graph-mask-risc `Gather` / `ScatterOr` / `GroupSum`. Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_01GXUahz73MZxtxWcfpHp9dG
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Understand this PR’s impact Explore downstream dependencies and potential security impact with Blast Radius. 📝 WalkthroughWalkthroughThe change adds indexed mask primitives, keyed masked reductions, indexed equality masks, and ordered key-run counting. It exports the APIs through the SIMD facade and adds unit and parity coverage for bounds, accumulation, tiling, and ordering behavior. ChangesIndexed masking operations
Priority: ⬇️ Low Estimated code review effort: 4 (Complex) | ~60 minutes Change: Feature Suggested reviewers: Merge Risk: 🔵 Low · up to The implementation is mergeable with a small documentation fix showing how finalization resets the carry. 🚥 Pre-merge checks | ✅ 5✅ Passed checks (5 passed)
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A rabbit hops through masks of bits Comment |
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…rough a fk hop `out[remap[index[i]]] += values[i]` over the mask, one pass. The shape of `SUM(line.amount) … GROUP BY partner.country`: the key lives on the foreign table and is reached through line.partner_id. The indirection is fused into the reduction so a remapped u32 key lane of N — exactly the intermediate the fold exists to avoid — is never materialised. Zero-fallback at both hops. 6 unit tests (agreement with the plain form on a precomputed key lane at n = 0/1/63/64/65/67/130, both drop arms, a 67-row tail against a naive reference with bad addresses at both hops), fourth arm of parity group 13 (0xD30/0xD31), first-hop guard disable-verified red then green. Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_01GXUahz73MZxtxWcfpHp9dG
…o it A fold kernel adds or ORs into the caller's demanded sink; the caller zeroes that sink once. Whole-buffer zeroing inside the kernel made every call population-sized in writes and broke tiled execution, where the same sink receives one call per tile. mask_gather_u32 is unchanged (its destination is its own output tile). Tests: 6 two-sided accumulation tests (each red with the zeroing restored, verified); parity group 13 gains three from-nonzero checks. Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_01GXUahz73MZxtxWcfpHp9dG
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…gn key `out[i] = fk[i] < foreign.len() && foreign[fk[i]] == v`, one pass, zero fallback on an out-of-range key. This is the join filter in factored form: the consumer needs neither a predicate plane over the foreign table nor a gathered mask over its own rows. Parity check 0xD40 in group 13. Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_01GXUahz73MZxtxWcfpHp9dG
…un distinct fold The five data-indexed primitives no longer describe themselves in foreign-key / join / table terms: parameters are `index` and `table`, docs speak of addresses and populations. `mask_gather_u32` and `mask_scatter_or_u32` carry their survival conditions — a gather reads only resident state into a tile-local output; a scatter writes only the demanded sink or the accumulator of the fold whose scalar leaves. New: `masked_key_run_count_u32` + `KeyRunCarry` — on a key-clustered lane, the distinct count over selected elements as a run fold with a two-word carry and no population-sized set. Documented as over-counting on an unclustered lane; parity 0xD50 threads the carry across uneven tiles against a seen-set reference. Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_01GXUahz73MZxtxWcfpHp9dG
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Returns `Option<usize>`: `None` the moment a key is smaller than the open run's key. Non-decreasing key order is the one clustering certificate checkable with O(1) state in the same pass, so it is the precondition — an unordered lane is refused, never over-counted; clustered-but-unsorted is refused too, deliberately. Parity 0xD51/0xD52 cover both halves. Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_01GXUahz73MZxtxWcfpHp9dG
…nselected-key counterexample Docs and tests say ordered/sorted. `keys = 1 2 1` with `1 0 1` selected is pinned: the order check inspects every key, so a fold that only saw survivors cannot count the two runs of 1 as one. Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_01GXUahz73MZxtxWcfpHp9dG
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September 21, 2026 22:28
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In `@src/simd_masking_ops.rs`:
- Around line 1322-1327: Add a documentation example to the public
KeyRunCarry::finish method showing the count-then-finish sequence, including the
returned count and that the carry is reset afterward. Keep the example
consistent with the method’s existing API and documentation style.
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Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_01GXUahz73MZxtxWcfpHp9dG
… vocabulary sweep - `None` now leaves `KeyRunCarry` exactly as on entry: the walk runs on a local copy and commits it only on `Some`. Contract: Some(n) → carry advanced; None → carry unchanged. Unit test `a_refused_call_commits_nothing_to_the_carry` + parity `0xD53` (descent rotated to the LAST element so a non-transactional walk is caught) — both disable-verified red-then-green. - Docs: "non-decreasing key lane" only (no projection/parent/child topology wording); "two words" → two scalar fields / O(1) carry. - Parity crate + unit tests: `fk`/`foreign` → `index`/`table`; header no longer names consumer verbs. - blackboard (20): the six-primitive entry rewritten once, consistently; the three sedimentary correction layers removed. Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_01GXUahz73MZxtxWcfpHp9dG
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T1 words the lance-graph mask-risc terminals lower onto, documented in address terms only (parameters
index/table/keys; no join, foreign-key, table-name or ERP vocabulary):mask_gather_u32— a bit of a resident mask read through an index lane. Survival condition stated: the source must be resident state, the output a tile of the caller's scratch.mask_scatter_or_u32— OR through an index lane into the caller's demanded sink (accumulates; caller zeroes once). Survival condition stated: the sink is the requested result or the accumulator of the fold whose scalar leaves, never a buffer another pass reads back.masked_group_sum_i32/masked_group_sum_i32_via— one-pass keyed segmented sum, key read directly or through an index lane (fused, no remapped key lane). Accumulate.eq_u32_via_to_mask— equality predicate evaluated through an index lane, no gathered mask in between.masked_key_run_count_u32+KeyRunCarry— on a non-decreasing key lane, the distinct count over selected elements as a run fold with an O(1) carry (two scalar fields). Contract: any descent, checked over every key (selected or not), returnsNoneand leaves the carry exactly as on entry;Some(n)advances it. An unordered lane is refused, never over-counted (1 2 1/1 0 1and contiguous-but-unsorted3 3 1 1are both pinned).All zero-fallback on out-of-range addresses, scalar by necessity (data-indexed), unit tests + parity group 13 (
0xD00–0xD53), accumulation and carry threaded across uneven tiles; the refusal and the carry-unchanged guarantee are disable-verified red-then-green.Consumer PR: AdaWorldAPI/lance-graph#1256 (its CI checks out ndarray master, so this merges first).
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