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perf(tune): shallower lazy lookahead probe (lazyDepth = chainDepth/4 or /8) at L8 #2781

Description

@kim-em

Shallower lazy lookahead probe at L8 (lazyDepth = chainDepth/4)

lazyDepth = chainDepth/2 uniformly, so at L8 every matched position pays a chain-256 walk at pos+1. libdeflate probes its first lookahead at half depth and its second at quarter; with a single probe, half is likely over-deep at the max chain depth. The docstring itself notes the deferral quality a shallower probe gives up is "slack."

Plan

  1. Sweep lazyDepth at L8 (chainDepth 512) over the current /2 (256), /4 (128), and /8 (64); measure ratio + matcher ms.
  2. Adopt the knee. One-line knob, heuristic, re-threading only.

🤖 Prepared with Claude Code

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    enhancementNew feature or requesttrack-dBenchmarking and verified optimization (PLAN.md Track D)

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