The peak search gave each of the 16384 directions to one thread, a chain of dependent
FP64 additions over 1572 bins - latency-bound on a card that holds far more threads.
Each direction's spectrum is now split into four consecutive runs of bins, one thread
each, and the runs' first-best peaks are combined in order with the same strict
comparison, so the first bin of highest prominence is still the one returned.
A run after the first sums its starting window afresh rather than carrying the running
sum in. The double sums of float magnitudes are exact unless a magnitude is below
~1e-9 of its window sum, so the background is the same double: 0 of 491520
directions differ in a synthetic still/rotation harness, and the hkl of 3000 stills
frames (-X fft) is byte-identical.
Kernel (isolated, RTX 5080): 0.87 -> 0.65 ms per call. The stills de-novo loop gains
~4% (128 -> 133 frames/s, ABAB, load ~10): the FFT chain as a whole is bound by GPU
memory bandwidth under the indexer pool's concurrency, so even a background in float
(6x faster kernel, not adopted) gives only ~9%. Rotation first pass: FFT kernels are
~3% of the indexing step.
Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>
leonarski_fandClaude Opus 5.5
c3cefebe8f