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blackboard (13): the tail-site count is 23, not 12 #312

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AdaWorldAPI merged 2 commits into from
Sep 16, 2026
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blackboard (13): the tail-site count is 23, not 12 #312

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blackboard (13): the tail-site count is 23, not 12 (12 tail + 7 ta + …
claude Sep 16, 2026
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blackboard (13): the 23 tail sites are two kinds — 12 predicate tails…
claude Sep 16, 2026
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13 changes: 13 additions & 0 deletions .claude/blackboard.md
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Expand Up @@ -48,6 +48,19 @@ built: `U64x4::ternlog` / `U64x2::ternlog` on the facade + rewire
`mask_ternlog`'s tail; an un-gated `pack<const L>` sibling of `pack_under` to
retire the 12 hand-rolled `if !tail.is_empty()` sites.

> *Correction 2026-09-16 (counted, after Codex on lance-graph #1244):* "12"
> is the number of branches literally named `tail`; the full set of
> hand-rolled tail branches in `simd_masking_ops.rs` at `c746735` is
> **23** — 12 `tail` + 7 `ta` + 3 `td` + 1 `ts` (`mask_shift_morton`).
> *Scope, corrected same day (Codex on #312):* they are TWO kinds. The 12
> `tail` branches are predicate-packing tails (one `values` slice → output
> words) — an un-gated `pack<const L>` retires exactly those. The 11
> `ta`/`td`/`ts` branches are mask-ALGEBRA tails (multi-input, in-place,
> and the accumulating Morton shift) — a packer cannot express them; they
> are what the VL descent (`U64x4::ternlog` / `U64x2::ternlog` + a
> `tail_descend` helper over the lane op) is for. Two follow-ups, one per
> kind; neither retires the other's set.

### 2. `examples/ternlogq_sparse_reapply_probe.rs` — FULL-WIDTH sparse frontier. NO.

1 024 words (65 536 rows, the MQ / `lgj_hop` population), `dst = src ∧ gate ∧
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