diff mbox series

[committed] libstdc++: Improve performance of chrono::utc_clock::now()

Message ID 20221116210014.1420128-1-jwakely@redhat.com
State Committed
Commit 629897ed80512a8618e08673c03d8482cbc42eef
Headers
Series [committed] libstdc++: Improve performance of chrono::utc_clock::now() |

Commit Message

Jonathan Wakely Nov. 16, 2022, 9 p.m. UTC 
  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(-)

Comments

Daniel Krügler Nov. 17, 2022, 6:29 a.m. UTC | #1 
Am Mi., 16. Nov. 2022 um 22:00 Uhr schrieb Jonathan Wakely via
Libstdc++ <libstdc++@gcc.gnu.org>:
>
> 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<seconds::rep> __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
Jonathan Wakely Nov. 17, 2022, 9:07 a.m. UTC | #2 
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++ <libstdc++@gcc.gnu.org>:
> >
> > 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<seconds::rep> __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 :-)
Daniel Krügler Nov. 17, 2022, 9:25 a.m. UTC | #3 
Am Do., 17. Nov. 2022 um 10:07 Uhr schrieb Jonathan Wakely
<jwakely.gcc@gmail.com>:
>
>
>
> 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++ <libstdc++@gcc.gnu.org>:
>> >
>> > 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<seconds::rep> __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
Jonathan Wakely Nov. 17, 2022, 9:47 a.m. UTC | #4 
On Thu, 17 Nov 2022 at 09:25, Daniel Krügler <daniel.kruegler@gmail.com>
wrote:

> Am Do., 17. Nov. 2022 um 10:07 Uhr schrieb Jonathan Wakely
> <jwakely.gcc@gmail.com>:
> >
> >
> >
> > 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++ <libstdc++@gcc.gnu.org>:
> >> >
> >> > 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<seconds::rep> __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.
Jonathan Wakely Nov. 17, 2022, 9:48 a.m. UTC | #5 
On Thu, 17 Nov 2022 at 09:47, Jonathan Wakely <jwakely@redhat.com> wrote:

>
>
> On Thu, 17 Nov 2022 at 09:25, Daniel Krügler <daniel.kruegler@gmail.com>
> wrote:
>
>> Am Do., 17. Nov. 2022 um 10:07 Uhr schrieb Jonathan Wakely
>> <jwakely.gcc@gmail.com>:
>> >
>> >
>> >
>> > 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++ <libstdc++@gcc.gnu.org>:
>> >> >
>> >> > 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<seconds::rep> __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?
Daniel Krügler Nov. 17, 2022, 9:56 a.m. UTC | #6 
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 <jwakely@redhat.com> wrote:
>>
>>
>>
>> On Thu, 17 Nov 2022 at 09:25, Daniel Krügler <daniel.kruegler@gmail.com> wrote:
>>>
>>> Am Do., 17. Nov. 2022 um 10:07 Uhr schrieb Jonathan Wakely
>>> <jwakely.gcc@gmail.com>:
>>> >
>>> >
>>> >
>>> > 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++ <libstdc++@gcc.gnu.org>:
>>> >> >
>>> >> > 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<seconds::rep> __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
Ville Voutilainen Nov. 17, 2022, 10:01 a.m. UTC | #7 
On Thu, 17 Nov 2022 at 11:57, Daniel Krügler via Libstdc++
<libstdc++@gcc.gnu.org> 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. :)
Jonathan Wakely Nov. 17, 2022, 10:30 a.m. UTC | #8 
On Thu, 17 Nov 2022 at 09:57, Daniel Krügler <daniel.kruegler@gmail.com>
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 <jwakely@redhat.com>
> wrote:
> >>
> >>
> >>
> >> On Thu, 17 Nov 2022 at 09:25, Daniel Krügler <daniel.kruegler@gmail.com>
> wrote:
> >>>
> >>> Am Do., 17. Nov. 2022 um 10:07 Uhr schrieb Jonathan Wakely
> >>> <jwakely.gcc@gmail.com>:
> >>> >
> >>> >
> >>> >
> >>> > 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++ <libstdc++@gcc.gnu.org>:
> >>> >> >
> >>> >> > 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<seconds::rep> __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<typename _Duration>
      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<seconds>(__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
:-)
diff mbox series

Patch

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<seconds::rep> __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,
+	      seconds{__pos - __first}
 	    };
 	  }
 	else