Last-bit change, not bit-exact: every partial whose frame does not contain its exact diffracting
condition gets a partiality - and so a slice-centroid walk along its Debye ring - that differs in
the last bits.
The partiality was (erf(b) - erf(a)) / 2 in float. Where the frame's slice lies in one tail of the
rocking curve both erf are near +-1, and their difference keeps only a few ulps of 1: glibc erf and
CUDA erff, one ulp apart, gave partialities ~1e-3 apart (relative) at p ~ 3e-5. The slice centroid
(RockingSliceCentroid_rad) divides by that partiality, and at zeta ~ 0.05 the walk it scales is
hundreds of pixels, so CPU and GPU placed such a reflection up to 0.1 px apart -
BraggPrediction_CPU_GPU_consistency_large_cell failed on one of them once --fmad=false (7ed970503)
moved the ulps. A slice in one tail now takes the same difference from erfcf, which keeps its relative
precision there; one helper (RockingSlicePartiality) serves both predictors.
Reflections placed more than 0.01 px apart by CPU and GPU in that test: 65 -> 0. BraggPrediction*,
BraggPredictionRot*, BraggPredictionRotGPU*, RockingSlice* pass. 7qij image passes 5.68/7.90 s ->
5.26/7.50 s (one lock hold; no cost).
Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01EizBKhTqrAYago9KJG3dA3
leonarski_fandClaude Opus 5.5
0b86ef5dab