The sort that orders every observation by (h,k,l,image_number) was not a total
order: two observations can genuinely share all four. The predictor emits BOTH
intersections of a reflection's rotation circle with the Ewald sphere, and near
the blind region - where zeta is smallest - the two are close enough in angle
that both are accepted on the same frame. Which of them came first was then
whatever the sort happened to produce.
That was observable. The combine takes on_ice from the FIRST member of a
rocking event, so the order decided whether a full was flagged as ice at all,
and its per-event sums are floating point, so it moved intensities in their
last bits. The observation's own index is now the final key, which orders them
by arrival - and, more usefully, makes the order unique, so it no longer
depends on which algorithm sorted it.
sigma never changes once it is uploaded, so 1/sigma is the same in all thirty
IRLS iterations of all three scaling iterations of all five scaling passes. It
was being recomputed every time: a 64-bit reciprocal is a hardware estimate
plus five refinement steps, and the profile put the three divisions in that
loop at 21 of its 31 double-precision instructions. It is computed once now, in
the pass that already streams every observation. The CPU has always hoisted it;
this is the GPU catching up. Same expression on the same operand, so the value
is what the loop used to compute, bit for bit.
Also: PrepScaleObsKernel is not a grid-stride loop, but the scale-fulls path
capped its grid at 65535 blocks like the grid-stride kernels around it. Above
16.8 million fulls that silently left the tail of sco_coeff/sco_ok stale. No
dataset here reaches it; the cap is simply wrong for that kernel.
And the AoS-to-SoA staging that feeds the GPU - the widest pass in Ingest,
reading an 80-byte struct and writing fourteen arrays out of it - ran on one
thread.
Full 24-crystal battery: same space group on all 24, none failed, one crystal
moved R_meas by 0.8 points with CC unchanged (it moves by that much between
runs of an identical binary). 15m32s -> 13m35s.
Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
