Re: [committed] libstdc++: Improve performance of chrono::utc_clock::now()
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.
- Daniel
Re: [committed] libstdc++: Improve performance of chrono::utc_clock::now()
On Thu, 17 Nov 2022, 06:30 Daniel Krügler via Libstdc++, <
libstd...@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 :-)
Re: [committed] libstdc++: Improve performance of chrono::utc_clock::now()
Am Do., 17. Nov. 2022 um 10:07 Uhr schrieb Jonathan Wakely
:
>
>
>
> On Thu, 17 Nov 2022, 06:30 Daniel Krügler via Libstdc++,
> 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?
Thanks,
- Daniel
Re: [committed] libstdc++: Improve performance of chrono::utc_clock::now()
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++, <
> libstd...@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.
Re: [committed] libstdc++: Improve performance of chrono::utc_clock::now()
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++, <
>> libstd...@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?
Re: [committed] libstdc++: Improve performance of chrono::utc_clock::now()
Am Do., 17. Nov. 2022 um 10:48 Uhr schrieb Jonathan Wakely :
>
>
>
> 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++,
>>> > 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.
Thanks,
- Daniel
Re: [committed] libstdc++: Improve performance of chrono::utc_clock::now()
On Thu, 17 Nov 2022 at 11:57, Daniel Krügler via Libstdc++ wrote: > > 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. Looks like someone's crunching to make a stage3 deadline, he gets a bit testy during those times. :) He'll return to his normal jolly self soon, don't worry, Daniel. :)
Re: [committed] libstdc++: Improve performance of chrono::utc_clock::now()
On Thu, 17 Nov 2022 at 09:57, Daniel Krügler
wrote:
> Am Do., 17. Nov. 2022 um 10:48 Uhr schrieb Jonathan Wakely <
> jwak...@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++, <
> libstd...@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)
