UseAtomBoxesByPlane handed its functor one grid point at a time, so the density
(gemmi's ExpSum/ExpAnisoSum with unsafe_expapprox) ran scalar - on the CPU path of
model validation the rigid body's density copies were 48% of all validation
CPU time (8sa8, perf). The walk over an atom's box on a plane is unchanged (same
order, same delta.x stepping) but now only collects the points within the radius
(index, d2, delta); the density functor then evaluates them a Gaussian at a time
over all points - each point still sums its Gaussians in gemmi's order from 0 -
in loops GCC vectorises (AVX2, no intrinsics), and adds them to the grid in walk
order. The mask functor zeroes the gathered points. Same grid, bit for bit, at
any thread count (ModelValidation_ParallelGriddingMatchesGemmi: iso + aniso,
five groups, 1 and 4 threads).
Measured (CPU build, --mode scale --model, shared machine, indicative): 8xtg
validation 28.1 -> 13.6 s wall, run total 665 -> 366 user-s (with the FitModelScale
commit); outputs identical.
Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01SVmAWnzCmRKAXVUCdc4iNi
leonarski_fandClaude Opus 5.5
03cd78322a