[BrianPugh]

Hey Sisong! I'm working on some compressor-speed optimizations; if you are okay with this relatively small PR, I'll open more to follow. These are all assuming that we care more about compressor-speed and compression-ratios over memory-usage/binary-size. Let me know if this assumption is incorrect.

This PR speeds up the compressor ~1.4–1.5x (CPU time) on binary deltas and firmware, up to 3.5x on repetitive text, with byte-identical output, by stopping the LCP match search once no remaining match can lower any cost.

• A match found by LCP has dict_pos>kShortPos, so its cost is at least

  cost[curi-1] + getSavedDictPosBit(kShortPos+1) + minDictLenBit[mLen]
  

  (minDictLenBit is the smaller of the near/far length bit counts, precomputed once).
• The search visits curMinLcp in decreasing order, so once no mLen<=curMinLcp can reach cost[curi+mLen-1], this match and every later (shorter) one writes nothing and leaves out_maxMatchLen unchanged.
• The check only applies below _k_kBMatchStep, so the big-match return is untouched.

On repetitive input the LCP walk used to run to its 2048 limit at most positions, and ~97% of those iterations could never lower a cost.

Benchmarks

Median CPU seconds (user+sys) of 9 runs, tinyuz -c-<dictSize> -p-1, clang -O3, Apple M3. Variants were interleaved in random order each round; in every cell the 9 runs span at most 4% of the median.

input	dict 256	dict 4k	dict 1m
binary delta, 0.99 MB	2.254 → 1.593 (1.42x)	2.190 → 1.482 (1.48x)	2.078 → 1.371 (1.52x)
binary deltas concatenated, 5.9 MB	10.99 → 7.70 (1.43x)	10.52 → 7.06 (1.49x)	10.12 → 6.66 (1.52x)
ESP32 firmware, 0.99 MB	0.355 → 0.258 (1.38x)	0.362 → 0.245 (1.48x)	0.455 → 0.298 (1.52x)
repetitive text, 0.97 MB	1.206 → 0.580 (2.08x)	1.221 → 0.344 (3.55x)	0.110 → 0.083 (1.32x)
random, 1 MB	0.170 → 0.172 (0.99x)	0.171 → 0.174 (0.98x)	0.214 → 0.218 (0.98x)

On random data (where the LCP walk is already short) the per-position bound check costs ~2%.

Additional Memory Consumption: one (_k_kBMatchStep)×4-byte table (2 KB) per matcher.

Byte-identity

476/476 outputs identical to the baseline (1d74ffa), and each decodes back to its input with the unchanged decoder: 17 files (real binary deltas, raw firmware, random, zeros, repetitive text, 0–65537-byte edge files) × dict {256, 1k, 3000, 4k, 64k, 1m, 16m} × {-c, -ci} × threads {1, 4}.

[BrianPugh]

stacked on #21 to fix CI