https://gcc.gnu.org/bugzilla/show_bug.cgi?id=121917
--- Comment #2 from GCC Commits <cvs-commit at gcc dot gnu.org> --- The master branch has been updated by Patrick Palka <ppa...@gcc.gnu.org>: https://gcc.gnu.org/g:349affa42c9fa47a12eb7f5f97f5650a77bbf014 commit r16-3842-g349affa42c9fa47a12eb7f5f97f5650a77bbf014 Author: Patrick Palka <ppa...@redhat.com> Date: Sat Sep 13 10:44:12 2025 -0400 libstdc++: Fix ranges::shuffle for non-sized range [PR121917] ranges::shuffle has a two-at-a-time PRNG optimization (copied from std::shuffle) that considers the PRNG width vs the size of the range. But in C++20 a random access sentinel isn't always sized so we can't unconditionally do __last - __first to obtain the size in constant time. We could instead use ranges::distance, but that'd take linear time for a non-sized sentinel which makes the optimization less clear of a win. So this patch instead makes us only consider this optimization for sized ranges. PR libstdc++/121917 libstdc++-v3/ChangeLog: * include/bits/ranges_algo.h (__shuffle_fn::operator()): Only consider the two-at-a-time PRNG optimization if the range is sized. * testsuite/25_algorithms/shuffle/constrained.cc (test03): New test. Reviewed-by: Jonathan Wakely <jwak...@redhat.com>
