blackboard (13): the tail-site count is 23, not 12 - #312
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…3 td + 1 ts) Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_01DCfrD5y19cvFc4AoyydXYv
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| > 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`) — and | ||
| > `pack<const L>` would retire all of them. Whether the Morton-shift tail |
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At c746735, the 11 newly counted ta/td/ts branches are not predicate-packing sites: they implement multi-input mask algebra, in-place updates, and the accumulating mask_shift_morton operation. An ungated sibling of pack_under, whose engine takes one values slice and packs predicate bits into output words, can replace the 12 literal tail predicate branches but cannot retire those other operations without a materially different abstraction. Claiming it retires all 23 therefore gives the follow-up an incorrect scope, and the next sentence already acknowledges that even the Morton case remains unresolved.
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Correct, and it splits the follow-up in two: the 12 tail branches are predicate-packing tails (one values slice → words) — an un-gated pack<const L> retires exactly those; the 11 ta/td/ts branches are mask-algebra tails (multi-input, in-place, the accumulating Morton shift) that a packer cannot express — they are the target of the VL descent (U64x4::ternlog / U64x2::ternlog + a tail_descend helper over the lane op), which is what the #311 probe measured. Note rewritten to say so; neither follow-up is claimed to retire the other's set.
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… (pack) + 11 algebra tails (VL descent), per Codex on #312 Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_01DCfrD5y19cvFc4AoyydXYv
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Hygiene-only, one dated correction appended to blackboard entry (13): "12 hand-rolled
if !tail.is_empty()sites" is the count of branches literally namedtail; the full set insimd_masking_ops.rsatc746735is 23 (12tail+ 7ta+ 3td+ 1tsinmask_shift_morton). Same correction already landed on the lance-graph epiphany via #1244 after Codex caught the named set one short. No code.🤖 Generated with Claude Code
https://claude.ai/code/session_01DCfrD5y19cvFc4AoyydXYv
Generated by Claude Code