Writing the merged reflections - p.mtz, p.cif, p.hkl, ~250 MB for 4nwv - takes 5.3 s on the
Windows laptop against 0.46 s on Linux. The mmCIF rows (twelve "%.4f" fields each) and the
HKLF 4 records (two "%.2f") are formatted with snprintf, ~50 M calls for 4nwv; the likely
Windows cost is the MSVC runtime's printf (slower float formatting, locale handling per call) -
not measured there yet. Fmt and the HKLF 4 number now go through std::to_chars(fixed, precision) where the
standard library has it for floating point (__cpp_lib_to_chars: libstdc++ 11+, MSVC); libc++
before macOS 13.3 does not, and keeps snprintf.
The same digits: both round the exact binary value correctly, halfway cases to even. Checked
against glibc on 20 M float-valued doubles at 4 and 2 decimals and on 8 M exact binary
fractions (every tie), 0 differences. On this machine (gcc-toolset-13) 52 against 194 ns a
field. p.hkl, the MTZ data and p.cif (apart from its provenance lines) byte-identical.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01PXc1zD1yxHqaR1DGdCTHL4
leonarski_fandClaude Opus 5.5
dccbf8b1da