Two measured, bit-equivalent perf wins. Each ships a criterion bench
(benches/features_bench.rs, new) with before/after numbers and a committed
bit-identity test — no perf claim without a measured before/after.
PSD FFT-planner caching (features.rs)
PowerSpectralDensity::from_csi_data re-planned a FftPlanner on EVERY frame,
and FeatureExtractor::extract calls it per frame on the hot path. New
from_csi_data_with_fft(csi, n, &Arc<dyn Fft>) reuses a plan cached in
FeatureExtractor (built once in new()). Bit-identical output
(psd_cached_fft_bit_identical_to_fresh, f64::to_bits over 6 sizes).
MEASURED (median ns/frame, criterion):
fft=64 5.84µs -> 1.89µs (3.09x)
fft=128 9.31µs -> 3.61µs (2.58x)
fft=256 13.77µs -> 6.73µs (2.04x)
DTW Sakoe-Chiba band (gesture.rs)
dtw_distance computed j_start/j_end but iterated the FULL 1..=m row,
continue-ing out-of-band — band constrained the path, not the work (O(n*m)).
Now iterates j_start..=j_end (O(n*band)), resetting only the two boundary
guard cells the recurrence reads, with endpoint reachability (|n-m|<=band)
at the return. Bit-identical across 12 shapes x 8 bands
(dtw_banded_bit_identical_to_fullrow).
MEASURED (median, criterion):
n=m=100 band=5 33.45µs -> 13.77µs (2.43x)
n=m=200 band=5 122.32µs -> 29.55µs (4.14x)
n=m=200 band=10 159.98µs -> 60.19µs (2.66x)
Reproduce:
cd v2 && cargo bench -p wifi-densepose-signal --no-default-features \
--bench features_bench
Co-Authored-By: claude-flow <ruv@ruv.net>
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