perf: vectorize partial-update bounding rect and segment encoder#94
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compute_bounding_rect was an O(W*H) pure-Python double loop run on every partial-capable upload (13.9ms @800x480, 71.6ms @1600x1200); replace with a numpy diff/any reduction (~300x). encode_segment_wire repeated the per-pixel packing loops; replace with flat np.packbits/LUT packing. Note the partial stream packs flat across row boundaries (no per-row byte padding), so the vectorized version uses flat packing, not axis=1. Verified byte-identical to the previous implementations across non-aligned widths and all color schemes. Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_01JRrm95f1qNZzDM9r2SB6KW
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Summary
Two hot spots on the partial-update path (
partial.py) were pure-Python per-pixel loops:compute_bounding_rect— an O(W·H) double loop run on every partial-capable upload, scanning the full width of every row even when unchanged. Measured 13.9 ms @800×480, 71.6 ms @1600×1200. Replaced with a numpy diff/anyreduction → 49 µs / 166 µs (~300×).encode_segment_wire— repeated the per-pixel packing loops. Replaced with flatnp.packbits/LUT packing.Correctness
Verified byte-identical to the previous implementations:
compute_bounding_rect: random diffs across sizes 122×250, 799×480, 127×3, 1×1, 5×4, 296×128.encode_segment_wire: all color schemes (MONO/BWRY/GRAYSCALE_4/BWGBRY/GRAYSCALE_16) across multiple crop rectangles that produce odd flat lengths.Test plan
uv run pytest -q→ 439 passedruff check,ruff format,mypyclean🤖 Generated with Claude Code