================
@@ -903,6 +904,180 @@ time_zone::__get_info(sys_seconds __time) const {
std::__throw_runtime_error("tzdb: corrupt db");
}
+enum class __position {
+ __beginning,
+ __middle,
+ __end,
+};
+
+// Determines the position of "__time" inside "__info".
+//
+// The code picks an arbitrary value to determine the "middle"
+// - Every time that is more than the threshold from a boundary, or
+// - Every value that is at the boundary sys_seconds::min() or
+// sys_seconds::max().
+//
+// If not in the middle, it returns __beginning or __end.
+[[nodiscard]] static __position __get_position(sys_seconds __time, const
sys_info __info) {
+ _LIBCPP_ASSERT_ARGUMENT_WITHIN_DOMAIN(
+ __time >= __info.begin && __time < __info.end, "A value outside the
range's position can't be determined.");
+
+ using _Tp = sys_seconds::rep;
+ // Africa/Freetown has a 4 day "zone"
+ // Africa/Freetown Fri Sep 1 00:59:59 1939 UT = Thu Aug 31 23:59:59 1939
-01 isdst=0 gmtoff=-3600
+ // Africa/Freetown Fri Sep 1 01:00:00 1939 UT = Fri Sep 1 00:20:00 1939
-0040 isdst=1 gmtoff=-2400
+ // Africa/Freetown Tue Sep 5 00:39:59 1939 UT = Mon Sep 4 23:59:59 1939
-0040 isdst=1 gmtoff=-2400
+ // Africa/Freetown Tue Sep 5 00:40:00 1939 UT = Mon Sep 4 23:40:00 1939
-01 isdst=0 gmtoff=-3600
+ //
+ // Originally used a one week threshold, but due to this switched to 1 day.
+ // This seems to work in practice.
+ //
+ // TODO TZDB Evaluate the proper threshold.
+ constexpr _Tp __threshold = 24 * 3600;
+
+ _Tp __upper = std::__add_sat(__info.begin.time_since_epoch().count(),
__threshold);
+ if (__time >= __info.begin && __time.time_since_epoch().count() < __upper)
+ return __info.begin != sys_seconds::min() ? __position::__beginning :
__position::__middle;
+
+ _Tp __lower = std::__sub_sat(__info.end.time_since_epoch().count(),
__threshold);
+ if (__time < __info.end && __time.time_since_epoch().count() >= __lower)
+ return __info.end != sys_seconds::max() ? __position::__end :
__position::__middle;
+
+ return __position::__middle;
+}
+
+[[nodiscard]] static local_info
+__get_info(local_seconds __local_time, const sys_info& __first, const
sys_info& __second) {
+ std::chrono::local_seconds __end_first{__first.end.time_since_epoch() +
__first.offset};
+ std::chrono::local_seconds __begin_second{__second.begin.time_since_epoch()
+ __second.offset};
+
+ if (__local_time < __end_first) {
+ if (__local_time >= __begin_second)
+ // |--------|
+ // |------|
+ // ^
+ return {local_info::ambiguous, __first, __second};
+
+ // |--------|
+ // |------|
+ // ^
+ return {local_info::unique, __first, sys_info{}};
+ }
+
+ if (__local_time < __begin_second)
+ // |--------|
+ // |------|
+ // ^
+ return {local_info::nonexistent, __first, __second};
+
+ // |--------|
+ // |------|
+ // ^
+ return {local_info::unique, __second, sys_info{}};
+}
+
+[[nodiscard]] _LIBCPP_AVAILABILITY_TZDB _LIBCPP_EXPORTED_FROM_ABI local_info
+time_zone::__get_info(local_seconds __local_time) const {
+ seconds __local_seconds = __local_time.time_since_epoch();
+
+ /* An example of a typical year with a DST switch displayed in local time.
+ *
+ * At the first of April the time goes forward one hour. This means the
+ * time marked with ~~ is not a valid local time. This is represented by the
+ * nonexistent value in local_info.result.
+ *
+ * At the first of November the time goes backward one hour. This means the
+ * time marked with ^^ happens twice. This is represented by the ambiguous
+ * value in local_info.result.
+ *
+ * 2020.11.01 2021.04.01 2021.11.01
+ * offset +05 offset +05 offset +05
+ * save 0s save 1h save 0s
+ * |-------------W----------|
+ * |----------W--------------|
+ * |-------------
+ * ~~ ^^
+ *
+ * These shifts can happen due to changes in the current time zone for a
+ * location. For example, Indian/Kerguelen switched only once. In 1950 from
an
+ * offset of 0 hours to an offset of +05 hours.
+ *
+ * During all these shifts the UTC time will have not gaps.
+ */
+
+ // The code needs to determine the system time for the local time. There is
no
+ // information available. Assume the offset between system time and local
time
+ // is 0s. This gives an initial estimate.
+ sys_seconds __guess{__local_seconds};
+ sys_info __info = __get_info(__guess);
+
+ // At this point the offset can be used to determine an estimate for the
local
+ // time. Before doing the determine the offset validate whether the local
time
+ // is the range [chrono::local_seconds::min(), chrono::local_seconds::max()).
+ if (__local_seconds < 0s && __info.offset > 0s)
+ if (__local_seconds - chrono::local_seconds::min().time_since_epoch() <
__info.offset)
+ return {-1, __info, {}};
+
+ if (__local_seconds > 0s && __info.offset < 0s)
+ if (chrono::local_seconds::max().time_since_epoch() - __local_seconds <
-__info.offset)
+ return {-2, __info, {}};
+
+ // Based on the information in the sys_info found the local time can be
+ // converted to a system time. This resulting time can be in the following
+ // locations of the sys_info found:
----------------
ldionne wrote:
```suggestion
// locations of the sys_info:
```
https://github.com/llvm/llvm-project/pull/89537
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