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,
+ seconds{__pos - __first}
};
}
else
--
2.38.1
