On Tue, Jun 30, 2026 at 3:10 PM Tomasz Kaminski <[email protected]> wrote:
> > > On Tue, Jun 30, 2026 at 2:52 PM Anlai Lu <[email protected]> wrote: > >> This is v3 of the patch series. Performance data: see v2 cover letter. >> Results are unchanged -- same stack-buffer + __ostream_insert approach. >> >> Patch 1 is unchanged from v2. >> >> Changes in Patch 2 from v2: >> >> - Dropped the format string parameter from __chrono_write. >> _S_empty_fs() is used directly, per Tomasz Kaminski's suggestion. >> All chrono types now share the same two call forms: >> __detail::__chrono_write(__os, __arg); >> __detail::__chrono_write(__os, __arg, __os.getloc()); >> >> - Removed __detail::__empty_fmt: no longer needed. >> >> - All remaining operator<< that used basic_stringstream now use >> __chrono_write (month_day, month_day_last, month_weekday, >> month_weekday_last, year_month, year_month_day_last, >> year_month_weekday, year_month_weekday_last, sys_days, local_time). >> >> - The only types not converted: duration (must forward stream flags >> and precision) and local_info (uses __formatter_chrono_info). >> > I think for local_info the __chrono_write would also give a correct result, > the formatter<local_info> uses __formatter_chrono_info and calls to > format_to > will pick it up. > However, now I wonder if it the output fits in 128B buffer, if it does I think the reduced duplication of the code would be beneficial (the _M_format_to overload for local_info) is esentially copy of operator<<. Previously std::format("{}", t) format was implemented by delegating throu operator<<, and I have reimplemented all the formatters (outside duration) to be independed, some time ago. And then flipping the logic to use operator<< instead of formatter was on my TODO list. So thank you for picking this up. > >> - Uses std::format_to_n (public API) instead of __do_vformat_to_n. >> >> Tested on x86_64-linux-gnu. libstdc++ testsuite (std/time/*) clean. >> All converted types verified byte-identical across C, en_US, de_DE, >> fr_FR, and zh_CN locales. >> > Do you see same kind of improvements as with your original patch? > >> >> Anlai Lu (2): >> libstdc++: Add stream state tests for chrono operator<< >> libstdc++: Use __chrono_write via _S_empty_fs for chrono ostream >> insertion >> >> libstdc++-v3/include/bits/chrono_io.h | 227 ++++-------------- >> .../testsuite/std/time/ostream_insert.cc | 163 +++++++++++++ >> 2 files changed, 212 insertions(+), 178 deletions(-) >> create mode 100644 libstdc++-v3/testsuite/std/time/ostream_insert.cc >> >> -- >> 2.34.1 >> >>
