The photon-weighted position sums were floats, so the centroid's last bit
depended on the build rather than on the data: gcc contracts the multiply-add
in AddPixel into an FMA under -march=x86-64-v3 and cannot at the baseline,
and MSVC does not contract at all under /fp:precise. The GPU extractor had to
match with __fmaf_rn, and the parity test still needed a two-ulp slack for
hosts that do not fuse.
Column, line and the per-pixel count are all integral, so the sums are exact
in int64 and both implementations reach the same bits with nothing to match.
The parity test now demands exact equality unconditionally and gets it,
including on a baseline build.
ConvertToImageCoordinates keeps the sums integral too: the raw -> image map
is a signed axis swap plus an integer translation, so it is applied to the
sums instead of to the centroid.
Drops the SpotToSave constructor, which had no callers and could not have
been converted without quantising the stored centroid.
Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
leonarski_fandClaude Opus 5
8f1b0b2281