simd: 16-byte strided care-masked matcher (ternary_match_strided16_to_mask)

[AdaWorldAPI]

What

ndarray::simd::ternary_match_strided16_to_mask is the full-width sibling of ternary_match_strided_to_mask.

• Signature: (bytes, first_offset, stride_bytes, count, pattern: &[u8; 16], care: &[u8; 16], out_words)
• Match rule: element i matches iff (reg[k] ^ pattern[k]) & care[k] == 0 for every k < 16. All 128 bits participate. The existing kernel covers only 12 bytes, the V3 facet payload.
• Execution model: the same as the 12-byte kernel.
  • scalar from_le_bytes gathers, with no alignment requirement;
  • U64x8 ternlog XOR_AND, now on two u64 halves;
  • a scalar tail;
  • full overwrite, with trailing bits zero.
• No population-sized scratch: the only scratch is two 16-lane arrays on the stack.
• The existing 12-byte matcher is unchanged.

Why

lance-graph's mask-risc can match a 12-byte facet payload in place (Pred::MatchFacetStrided). A care-masked match over a whole 16-byte register currently requires extracting hi/lo u64 columns first, which materialises them. This kernel removes that need. The lance-graph exposure follows in a dependent PR.

Tests

• ternary_match_strided16_equals_bytewise_reference compares against a byte-wise scalar reference.
  • Care masks: none, all, first byte, last byte, the bits either side of the 64-bit boundary, and 4 random masks.
  • Row counts: 0, 1, 15, 16, 17, 63, 64, 65, 130.
  • Strides 16, 24 and 512, from a misaligned offset.
  • A full-width hit is planted at row 0.
• ternary_match_strided16_sees_bytes_past_twelve: a row that differs only in byte 15 misses under full care. The 12-byte matcher calls the same row a hit. With byte 15 set to don't-care, the row matches again.
• ternary_match_strided16_rejects_a_last_element_past_the_buffer: an element that would read past the end of the buffer panics.
• Doc test.

Disable runs, each red then green:

• ignore bytes 12..15 (the 12-byte behaviour);
• ignore care on the low half;
• drop the scalar tail;
• ignore the high half in the vector path.

cargo clippy --lib --tests -D warnings is clean. Locally I ran only the default dispatch; the other backends are covered by simd-matrix.yaml.

🤖 Generated with Claude Code

https://claude.ai/code/session_017PWtMb9jQ4gof5g4y2jzNt

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Generated by Claude Code

Summary by CodeRabbit

• New Features
  • Added matching for 16-byte records using pattern and care masks. A record matches when every cared-for byte equals its corresponding pattern byte.
  • Results are written as a packed bitmask, with each bit representing whether a record matches. The operation supports strided records and handles records that do not fit in full processing groups.
  • Input bounds and output capacity are checked before processing.

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📚 Code guidelines (1)

CLAUDE.md — auto-discovered

📝 Walkthrough

Walkthrough

Adds ternary_match_strided16_to_mask for 16-byte strided records. The function checks bounds, overwrites the packed output, and compares full groups using two 64-bit halves, with a scalar tail. The std-gated SIMD facade exports the function. Tests compare it with a bytewise reference.

Changes

16-byte strided matcher

Layer / File(s)	Summary
Matcher implementation and validation src/simd_masking_ops.rs, src/simd.rs, .claude/blackboard.md	Adds and exports the 16-byte matcher. It checks output capacity and bounds, overwrites the output, and compares records in 16-record groups with a scalar tail. Tests cover varied masks, strides, lengths, misaligned starts, byte 15, and out-of-bounds access. The blackboard records the implementation and verification limits.

Priority: ⬇️ Low

Estimated code review effort: 3 (Moderate) | ~20 minutes

Change: Feature

Suggested reviewers: claude

Merge Risk: 🔵 Low · up to cc4e8

The new matcher appears functionally sound, but its public API shape departs from the project's SIMD contract. Align the API with that contract, or explicitly accept the deviation, before merging.

🚥 Pre-merge checks | ✅ 5

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Title check	✅ Passed	The title clearly identifies the 16-byte strided care-masked matcher, which is the main change.
Docstring Coverage	✅ Passed	Docstring coverage is 100.00% which is sufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 8 functions across 2 files. (1 skipped: 1 …
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---

_{A rabbit checks each byte with care,
Sixteen hop into a mask,
Two halves meet in lanes of light,
Then scalar feet finish the task,
The output clears from end to end,
And byte fifteen joins the dance.}

_{Comment @coderabbitai help to get the list of available commands.}

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Actionable comments posted: 1

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Inline comments:
Review comments at @src/simd_masking_ops.rs:
- Line 3787: Convert ternary_match_strided16_to_mask from a public free function
into a method on the relevant typed wrapper, and shape its batch primitive to
accept a closure parameter, preserving the existing matching behavior.

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