[pfoxARM]

• Adds Neon squared-L2 kernels for int8 and uint8 inputs, using absolute differences and dot-product accumulation.
• Changes both kernels accumulators from eight lanes to four
• Expand tests with boundary cases for minimum and maximum input

This changes:

• diskann-vector/src/distance/simd.rs
• diskann-wide/src/arch/aarch64/algorithms.rs

Both myself and Utsav Goel have worked on this together.

[Copilot]

🟢 Approval recommended

No active review issues remain for the AArch64 Neon squared-L2 kernel and distance-schema updates.

No open issues 🎉

What changed in this PR

This PR optimizes DiskANN’s AArch64 Neon squared-L2 kernels for signed and unsigned 8-bit vectors, keeping the distance schemas aligned with the updated kernels.

Changes:

• Replaces widening subtraction and multiplication with absolute differences and dot-product accumulation.
• Reduces accumulators from eight lanes to four and updates scalar-tail handling.
• Expands kernel tests with minimum and maximum input and accumulator values.

File	Description
diskann-wide/​src/​arch/​aarch64/​algorithms.rs	Updates both Neon kernels and adds boundary-case tests.
diskann-vector/​src/​distance/​simd.rs	Adapts Neon L2 schemas and scalar tails to four-lane accumulators.

_{Review effort: Balanced}

[Mark Hildebrand (hildebrandmw)]

One small request, since we have an opportunity here to delete even more code.

[Copilot]

🟢 Approval recommended

No active review issues block approval of the Neon squared-L2 kernel changes.

No open issues 🎉

_{Review effort: Balanced}

[Codecov Comments Bot (codecov-commenter)]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 91.06%. Comparing base (413be59) to head (247be00).
⚠️ Report is 6 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1540      +/-   ##
==========================================
+ Coverage   91.01%   91.06%   +0.04%     
==========================================
  Files         602      602              
  Lines      124144   124137       -7     
==========================================
+ Hits       112994   113045      +51     
+ Misses      11150    11092      -58     

Flag	Coverage Δ
miri	91.06% <ø> (+0.04%)	⬆️
unittests	90.77% <ø> (+0.04%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Files with missing lines	Coverage Δ
diskann-vector/src/distance/simd.rs	78.15% <ø> (ø)

... and 23 files with indirect coverage changes

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