On Thu, 17 Nov 2022 at 09:57, Daniel Krügler wrote: > Am Do., 17. Nov. 2022 um 10:48 Uhr schrieb Jonathan Wakely < > jwakely@redhat.com>: > > > > > > > > On Thu, 17 Nov 2022 at 09:47, Jonathan Wakely > wrote: > >> > >> > >> > >> On Thu, 17 Nov 2022 at 09:25, Daniel Krügler > wrote: > >>> > >>> Am Do., 17. Nov. 2022 um 10:07 Uhr schrieb Jonathan Wakely > >>> : > >>> > > >>> > > >>> > > >>> > On Thu, 17 Nov 2022, 06:30 Daniel Krügler via Libstdc++, < > libstdc++@gcc.gnu.org> wrote: > >>> >> > >>> >> Am Mi., 16. Nov. 2022 um 22:00 Uhr schrieb Jonathan Wakely via > >>> >> Libstdc++ : > >>> >> > > >>> >> > Tested x86_64-linux. Pushed to trunk. > >>> >> > > >>> >> > -- >8 -- > >>> >> > > >>> >> > We can use an array instead of a std::vector, and we can avoid the > >>> >> > binary search for the common case of a time point after the most > recent > >>> >> > leap second. On one system where I tested this, utc_clock::now() > now > >>> >> > takes about 16ns instead of 31ns. > >>> >> > > >>> >> > libstdc++-v3/ChangeLog: > >>> >> > > >>> >> > * include/std/chrono (get_leap_second_info): Optimize. > >>> >> > --- > >>> >> > libstdc++-v3/include/std/chrono | 31 > ++++++++++++++++++++++++------- > >>> >> > 1 file changed, 24 insertions(+), 7 deletions(-) > >>> >> > > >>> >> > diff --git a/libstdc++-v3/include/std/chrono > b/libstdc++-v3/include/std/chrono > >>> >> > index 90b73f8198e..2468023f6c5 100644 > >>> >> > --- a/libstdc++-v3/include/std/chrono > >>> >> > +++ b/libstdc++-v3/include/std/chrono > >>> >> > @@ -2747,9 +2747,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION > >>> >> > { > >>> >> > if constexpr (is_same_v<_Duration, seconds>) > >>> >> > { > >>> >> > - // TODO move this function into the library and get > leaps from tzdb. > >>> >> > - vector __leaps > >>> >> > - { > >>> >> > + const seconds::rep __leaps[] { > >>> >> > 78796800, // 1 Jul 1972 > >>> >> > 94694400, // 1 Jan 1973 > >>> >> > 126230400, // 1 Jan 1974 > >>> >> > @@ -2778,12 +2776,31 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION > >>> >> > 1435708800, // 1 Jul 2015 > >>> >> > 1483228800, // 1 Jan 2017 > >>> >> > }; > >>> >> > + // The list above is known to be valid until > 2023-06-28 00:00:00 UTC > >>> >> > + const seconds::rep __expires = 1687910400; > >>> >> > + const seconds::rep __s = > __ut.time_since_epoch().count(); > >>> >> > > >>> >> > - auto __s = __ut.time_since_epoch().count(); > >>> >> > - auto __pos = std::upper_bound(__leaps.begin(), > __leaps.end(), __s); > >>> >> > + const seconds::rep* __first = std::begin(__leaps); > >>> >> > + const seconds::rep* __last = std::end(__leaps); > >>> >> > + > >>> >> > + if (__s > __expires) > >>> >> > + { > >>> >> > + // TODO: use updated leap_seconds from tzdb > >>> >> > +#if 0 > >>> >> > + auto __db = get_tzdb_list().begin(); > >>> >> > + __first = __db->leap_seconds.data(); > >>> >> > + __last = __first + __db->leap_seconds.size(); > >>> >> > +#endif > >>> >> > + } > >>> >> > + > >>> >> > + // Don't bother searching the list if we're after the > last one. > >>> >> > + if (__s > __last[-1]) > >>> >> > + return { false, seconds(__last - __first) }; > >>> >> > + > >>> >> > + auto __pos = std::upper_bound(__first, __last, __s); > >>> >> > return { > >>> >> > - __pos != __leaps.begin() && __pos[-1] == __s, > >>> >> > - seconds{__pos - __leaps.begin()} > >>> >> > + __pos != begin(__leaps) && __pos[-1] == __s, > >>> >> > >>> >> The inconsistency between usage of std::begin versus begin here > seems > >>> >> odd and I'm wondering why instead of "begin(__leaps)" the above > >>> >> introduced "__first" variable is not used instead. > >>> > > >>> > > >>> > Because this code is going to be changed again soon, this is a > partial merge from a local branch with the TODO fixed. Yes, it's > inconsistent, but it works correctly and it's not my priority right now :-) > >>> > >>> What about the suggestion to use the already existing "__first" > >>> variable instead of the begin call? > >> > >> > >> It's an array, the begin call is free. > > > > Do you really want me to stop working on the missing time zone support > to test and commit that change? > > I do not. I was reviewing and hoping to make a useful comment. > > It is useful and I do appreciate the review, but like I said, the code is going to change soon anyway, so I don't see any point making tiny stylistic changes now (there's no problem with ADL here, as the array contains int64_t values, and calling begin on an array is cheap). This is what I have in my local branch: template leap_second_info get_leap_second_info(const utc_time<_Duration>& __ut) { if (__ut < utc_time<_Duration>{}) [[unlikely]] return {}; if constexpr (is_same_v<_Duration, seconds>) { const seconds::rep __leaps[] { 78796800, // 1 Jul 1972 94694400, // 1 Jan 1973 126230400, // 1 Jan 1974 157766400, // 1 Jan 1975 189302400, // 1 Jan 1976 220924800, // 1 Jan 1977 252460800, // 1 Jan 1978 283996800, // 1 Jan 1979 315532800, // 1 Jan 1980 362793600, // 1 Jul 1981 394329600, // 1 Jul 1982 425865600, // 1 Jul 1983 489024000, // 1 Jul 1985 567993600, // 1 Jan 1988 631152000, // 1 Jan 1990 662688000, // 1 Jan 1991 709948800, // 1 Jul 1992 741484800, // 1 Jul 1993 773020800, // 1 Jul 1994 820454400, // 1 Jan 1996 867715200, // 1 Jul 1997 915148800, // 1 Jan 1999 1136073600, // 1 Jan 2006 1230768000, // 1 Jan 2009 1341100800, // 1 Jul 2012 1435708800, // 1 Jul 2015 1483228800, // 1 Jan 2017 }; // The list above is known to be valid until 2023-06-28 00:00:00 UTC const seconds::rep __expires = 1687910400; const seconds::rep __s = __ut.time_since_epoch().count(); if (__s < __expires) { const seconds::rep* __first = std::begin(__leaps); const seconds::rep* __last = std::end(__leaps); // Don't bother searching the list if we're after the last one. if (__s > __last[-1]) return { false, seconds(__last - __first) }; auto __pos = std::upper_bound(__first, __last, __s); return { __pos != __first && __pos[-1] == __s, seconds{__pos - __first} }; } else { // use updated leap_seconds from tzdb auto __db = get_tzdb_list().begin(); auto __first = __db->leap_seconds.begin(); auto __last = __db->leap_seconds.end(); sys_seconds __ss(__ut.time_since_epoch()); auto __pos = std::upper_bound(__first, __last, __ss); return { __pos != __first && __pos[-1] == __ss, seconds{__pos - __first} }; } } else { auto __s = chrono::time_point_cast(__ut); return chrono::get_leap_second_info(__s); } } But that can't be pushed to trunk now because get_tzdb_list() isn't defined on trunk yet. If you have any comments about *this* version, I'll be happy to hear them :-)