On 27/04/20 17:34 -0400, Patrick Palka via Libstdc++ wrote:
This implements the proposed resolution of LWG 3433, which fixes subrange::advance when called with a negative argument.Tested on x86_64-pc-linux-gnu, does this look OK to commit? libstdc++-v3/ChangeLog: LWG 3433 subrange::advance(n) has UB when n < 0 * include/std/ranges (subrange::prev): Fix typo. (subrange::advance): Handle a negative argument as per the proposed resolution of LWG 3433. * testsuite/std/ranges/subrange/lwg3433.cc: New test. --- libstdc++-v3/include/std/ranges | 25 +++-- .../testsuite/std/ranges/subrange/lwg3433.cc | 96 +++++++++++++++++++ 2 files changed, 111 insertions(+), 10 deletions(-) create mode 100644 libstdc++-v3/testsuite/std/ranges/subrange/lwg3433.cc diff --git a/libstdc++-v3/include/std/ranges b/libstdc++-v3/include/std/ranges index 8f91598c26e..565366a8d2f 100644 --- a/libstdc++-v3/include/std/ranges +++ b/libstdc++-v3/include/std/ranges @@ -353,23 +353,28 @@ namespace ranges requires bidirectional_iterator<_It> { auto __tmp = *this; - __tmp.advance(--__n); + __tmp.advance(-__n); return __tmp; } constexpr subrange& advance(iter_difference_t<_It> __n) { + // We incorporate the proposed resolution of LWG 3433 here, + // avoiding undefined behavior when __n < 0.
Please replace or extend this comment with our convention for marking issue resolutions: // _GLIBCXX_RESOLVE_LIB_DEFECTS // 3343. subrange::advance(n) has UB when n < 0 OK for trunk with that change, thanks.
