//===----------------------------------------------------------------------===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
// For information see https://libcxx.llvm.org/DesignDocs/TimeZone.html
// TODO TZDB look at optimizations
//
// The current algorithm is correct but not efficient. For example, in a named
// rule based continuation finding the next rule does quite a bit of work,
// returns the next rule and "forgets" its state. This could be better.
//
// It would be possible to cache lookups. If a time for a zone is calculated its
// sys_info could be kept and the next lookup could test whether the time is in
// a "known" sys_info. The wording in the Standard hints at this slowness by
// "suggesting" this could be implemented on the user's side.
// TODO TZDB look at removing quirks
//
// The code has some special rules to adjust the timing at the continuation
// switches. This works correctly, but some of the places feel odd. It would be
// good to investigate this further and see whether all quirks are needed or
// that there are better fixes.
//
// These quirks often use a 12h interval; this is the scan interval of zdump,
// which implies there are no sys_info objects with a duration of less than 12h.
#include <algorithm>
#include <cctype>
#include <chrono>
#include <expected>
#include <map>
#include <numeric>
#include <ranges>
#include "include/tzdb/time_zone_private.h"
#include "include/tzdb/tzdb_list_private.h"
// TODO TZDB remove debug printing
#ifdef PRINT
# include <print>
#endif
_LIBCPP_BEGIN_NAMESPACE_STD
#ifdef PRINT
template <>
struct formatter<chrono::sys_info, char> {
template <class ParseContext>
constexpr typename ParseContext::iterator parse(ParseContext& ctx) {
return ctx.begin();
}
template <class FormatContext>
typename FormatContext::iterator format(const chrono::sys_info& info, FormatContext& ctx) const {
return std::format_to(
ctx.out(), "[{}, {}) {:%Q%q} {:%Q%q} {}", info.begin, info.end, info.offset, info.save, info.abbrev);
}
};
#endif
namespace chrono {
//===----------------------------------------------------------------------===//
// Details
//===----------------------------------------------------------------------===//
struct __sys_info {
sys_info __info;
bool __can_merge; // Can the returned sys_info object be merged with
};
// Return type for helper function to get a sys_info.
// - The expected result returns the "best" sys_info object. This object can be
// before the requested time. Sometimes sys_info objects from different
// continuations share their offset, save, and abbrev and these objects are
// merged to one sys_info object. The __can_merge flag determines whether the
// current result can be merged with the next result.
// - The unexpected result means no sys_info object was found and the time is
// the time to be used for the next search iteration.
using __sys_info_result = expected<__sys_info, sys_seconds>;
template <ranges::forward_range _Range,
class _Type,
class _Proj = identity,
indirect_strict_weak_order<const _Type*, projected<ranges::iterator_t<_Range>, _Proj>> _Comp = ranges::less>
[[nodiscard]] static ranges::borrowed_iterator_t<_Range>
__binary_find(_Range&& __r, const _Type& __value, _Comp __comp = {}, _Proj __proj = {}) {
auto __end = ranges::end(__r);
auto __ret = ranges::lower_bound(ranges::begin(__r), __end, __value, __comp, __proj);
if (__ret == __end)
return __end;
// When the value does not match the predicate it's equal and a valid result
// was found.
return !std::invoke(__comp, __value, std::invoke(__proj, *__ret)) ? __ret : __end;
}
// Format based on https://data.iana.org/time-zones/tz-how-to.html
//
// 1 a time zone abbreviation that is a string of three or more characters that
// are either ASCII alphanumerics, "+", or "-"
// 2 the string "%z", in which case the "%z" will be replaced by a numeric time
// zone abbreviation
// 3 a pair of time zone abbreviations separated by a slash ('/'), in which
// case the first string is the abbreviation for the standard time name and
// the second string is the abbreviation for the daylight saving time name
// 4 a string containing "%s", in which case the "%s" will be replaced by the
// text in the appropriate Rule's LETTER column, and the resulting string
// should be a time zone abbreviation
//
// Rule 1 is not strictly validated since America/Barbados uses a two letter
// abbreviation AT.
[[nodiscard]] static string
__format(const __tz::__continuation& __continuation, const string& __letters, seconds __save) {
bool __shift = false;
string __result;
for (char __c : __continuation.__format) {
if (__shift) {
switch (__c) {
case 's':
std::ranges::copy(__letters, std::back_inserter(__result));
break;
case 'z': {
if (__continuation.__format.size() != 2)
std::__throw_runtime_error(
std::format("corrupt tzdb FORMAT field: %z should be the entire contents, instead contains '{}'",
__continuation.__format)
.c_str());
chrono::hh_mm_ss __offset{__continuation.__stdoff + __save};
if (__offset.is_negative()) {
__result += '-';
__offset = chrono::hh_mm_ss{-(__continuation.__stdoff + __save)};
} else
__result += '+';
if (__offset.minutes() != 0min)
std::format_to(std::back_inserter(__result), "{:%H%M}", __offset);
else
std::format_to(std::back_inserter(__result), "{:%H}", __offset);
} break;
default:
std::__throw_runtime_error(
std::format("corrupt tzdb FORMAT field: invalid sequence '%{}' found, expected %s or %z", __c).c_str());
}
__shift = false;
} else if (__c == '/') {
if (__save != 0s)
__result.clear();
else
break;
} else if (__c == '%') {
__shift = true;
} else if (__c == '+' || __c == '-' || std::isalnum(__c)) {
__result.push_back(__c);
} else {
std::__throw_runtime_error(
std::format(
"corrupt tzdb FORMAT field: invalid character '{}' found, expected +, -, or an alphanumeric value", __c)
.c_str());
}
}
if (__shift)
std::__throw_runtime_error("corrupt tzdb FORMAT field: input ended with the start of the escape sequence '%'");
if (__result.empty())
std::__throw_runtime_error("corrupt tzdb FORMAT field: result is empty");
return __result;
}
[[nodiscard]] static sys_seconds __to_sys_seconds(year_month_day __ymd, seconds __seconds) {
seconds __result = static_cast<sys_days>(__ymd).time_since_epoch() + __seconds;
return sys_seconds{__result};
}
[[nodiscard]] static seconds __at_to_sys_seconds(const __tz::__continuation& __continuation) {
switch (__continuation.__at.__clock) {
case __tz::__clock::__local:
return __continuation.__at.__time - __continuation.__stdoff -
std::visit(
[](const auto& __value) {
using _Tp = decay_t<decltype(__value)>;
if constexpr (same_as<_Tp, monostate>)
return chrono::seconds{0};
else if constexpr (same_as<_Tp, __tz::__save>)
return chrono::duration_cast<seconds>(__value.__time);
else if constexpr (same_as<_Tp, std::string>)
// For a named rule based continuation the SAVE depends on the RULE
// active at the end. This should be determined separately.
return chrono::seconds{0};
else
static_assert(sizeof(_Tp) == 0); // TODO TZDB static_assert(false); after droping clang-16 support
std::__libcpp_unreachable();
},
__continuation.__rules);
case __tz::__clock::__universal:
return __continuation.__at.__time;
case __tz::__clock::__standard:
return __continuation.__at.__time - __continuation.__stdoff;
}
std::__libcpp_unreachable();
}
[[nodiscard]] static year_month_day __to_year_month_day(year __year, month __month, __tz::__on __on) {
return std::visit(
[&](const auto& __value) {
using _Tp = decay_t<decltype(__value)>;
if constexpr (same_as<_Tp, chrono::day>)
return year_month_day{__year, __month, __value};
else if constexpr (same_as<_Tp, weekday_last>)
return year_month_day{static_cast<sys_days>(year_month_weekday_last{__year, __month, __value})};
else if constexpr (same_as<_Tp, __tz::__constrained_weekday>)
return __value(__year, __month);
else
static_assert(sizeof(_Tp) == 0); // TODO TZDB static_assert(false); after droping clang-16 support
std::__libcpp_unreachable();
},
__on);
}
[[nodiscard]] static sys_seconds __until_to_sys_seconds(const __tz::__continuation& __continuation) {
// Does UNTIL contain the magic value for the last continuation?
if (__continuation.__year == chrono::year::min())
return sys_seconds::max();
year_month_day __ymd = chrono::__to_year_month_day(__continuation.__year, __continuation.__in, __continuation.__on);
return chrono::__to_sys_seconds(__ymd, chrono::__at_to_sys_seconds(__continuation));
}
// Holds the UNTIL time for a continuation with a named rule.
//
// Unlike continuations with an fixed SAVE named rules have a variable SAVE.
// This means when the UNTIL uses the local wall time the actual UNTIL value can
// only be determined when the SAVE is known. This class holds that abstraction.
class __named_rule_until {
public:
explicit __named_rule_until(const __tz::__continuation& __continuation)
: __until_{chrono::__until_to_sys_seconds(__continuation)},
__needs_adjustment_{
// The last continuation of a ZONE has no UNTIL which basically is
// until the end of _local_ time. This value is expressed by
// sys_seconds::max(). Subtracting the SAVE leaves large value.
// However SAVE can be negative, which would add a value to maximum
// leading to undefined behaviour. In practice this often results in
// an overflow to a very small value.
__until_ != sys_seconds::max() && __continuation.__at.__clock == __tz::__clock::__local} {}
// Gives the unadjusted until value, this is useful when the SAVE is not known
// at all.
sys_seconds __until() const noexcept { return __until_; }
bool __needs_adjustment() const noexcept { return __needs_adjustment_; }
// Returns the UNTIL adjusted for SAVE.
sys_seconds operator()(seconds __save) const noexcept { return __until_ - __needs_adjustment_ * __save; }
private:
sys_seconds __until_;
bool __needs_adjustment_;
};
[[nodiscard]] static seconds __at_to_seconds(seconds __stdoff, const __tz::__rule& __rule) {
switch (__rule.__at.__clock) {
case __tz::__clock::__local:
// Local time and standard time behave the same. This is not
// correct. Local time needs to adjust for the current saved time.
// To know the saved time the rules need to be known and sorted.
// This needs a time so to avoid the chicken and egg adjust the
// saving of the local time later.
return __rule.__at.__time - __stdoff;
case __tz::__clock::__universal:
return __rule.__at.__time;
case __tz::__clock::__standard:
return __rule.__at.__time - __stdoff;
}
std::__libcpp_unreachable();
}
[[nodiscard]] static sys_seconds __from_to_sys_seconds(seconds __stdoff, const __tz::__rule& __rule, year __year) {
year_month_day __ymd = chrono::__to_year_month_day(__year, __rule.__in, __rule.__on);
seconds __at = chrono::__at_to_seconds(__stdoff, __rule);
return chrono::__to_sys_seconds(__ymd, __at);
}
[[nodiscard]] static sys_seconds __from_to_sys_seconds(seconds __stdoff, const __tz::__rule& __rule) {
return chrono::__from_to_sys_seconds(__stdoff, __rule, __rule.__from);
}
[[nodiscard]] static const vector<__tz::__rule>&
__get_rules(const __tz::__rules_storage_type& __rules_db, const string& __rule_name) {
auto __result = chrono::__binary_find(__rules_db, __rule_name, {}, [](const auto& __p) { return __p.first; });
if (__result == std::end(__rules_db))
std::__throw_runtime_error(("corrupt tzdb: rule '" + __rule_name + " 'does not exist").c_str());
return __result->second;
}
// Returns the letters field for a time before the first rule.
//
// Per https://data.iana.org/time-zones/tz-how-to.html
// One wrinkle, not fully explained in zic.8.txt, is what happens when switching
// to a named rule. To what values should the SAVE and LETTER data be
// initialized?
//
// 1 If at least one transition has happened, use the SAVE and LETTER data from
// the most recent.
// 2 If switching to a named rule before any transition has happened, assume
// standard time (SAVE zero), and use the LETTER data from the earliest
// transition with a SAVE of zero.
//
// This function implements case 2.
[[nodiscard]] static string __letters_before_first_rule(const vector<__tz::__rule>& __rules) {
auto __letters =
__rules //
| views::filter([](const __tz::__rule& __rule) { return __rule.__save.__time == 0s; }) //
| views::transform([](const __tz::__rule& __rule) { return __rule.__letters; }) //
| views::take(1);
if (__letters.empty())
std::__throw_runtime_error("corrupt tzdb: rule has zero entries");
return __letters.front();
}
// Determines the information based on the continuation and the rules.
//
// There are several special cases to take into account
//
// === Entries before the first rule becomes active ===
// Asia/Hong_Kong
// 9 - JST 1945 N 18 2 // (1)
// 8 HK HK%sT // (2)
// R HK 1946 o - Ap 21 0 1 S // (3)
// There (1) is active until Novemer 18th 1945 at 02:00, after this time
// (2) becomes active. The first rule entry for HK (3) becomes active
// from April 21st 1945 at 01:00. In the period between (2) is active.
// This entry has an offset.
// This entry has no save, letters, or dst flag. So in the period
// after (1) and until (3) no rule entry is associated with the time.
[[nodiscard]] static sys_info __get_sys_info_before_first_rule(
sys_seconds __begin,
sys_seconds __end,
const __tz::__continuation& __continuation,
const vector<__tz::__rule>& __rules) {
return sys_info{
__begin,
__end,
__continuation.__stdoff,
chrono::minutes(0),
chrono::__format(__continuation, __letters_before_first_rule(__rules), 0s)};
}
// Returns the sys_info object for a time before the first rule.
// When this first rule has a SAVE of 0s the sys_info for the time before the
// first rule and for the first rule are identical and will be merged.
[[nodiscard]] static sys_info __get_sys_info_before_first_rule(
sys_seconds __begin,
sys_seconds __rule_end, // The end used when SAVE != 0s
sys_seconds __next_end, // The end used when SAVE == 0s the times are merged
const __tz::__continuation& __continuation,
const vector<__tz::__rule>& __rules,
vector<__tz::__rule>::const_iterator __rule) {
if (__rule->__save.__time != 0s)
return __get_sys_info_before_first_rule(__begin, __rule_end, __continuation, __rules);
return sys_info{
__begin, __next_end, __continuation.__stdoff, 0min, chrono::__format(__continuation, __rule->__letters, 0s)};
}
[[nodiscard]] static seconds __at_to_seconds(seconds __stdoff, seconds __save, const __tz::__rule& __rule) {
switch (__rule.__at.__clock) {
case __tz::__clock::__local:
return __rule.__at.__time - __stdoff - __save;
case __tz::__clock::__universal:
return __rule.__at.__time;
case __tz::__clock::__standard:
return __rule.__at.__time - __stdoff;
}
std::__libcpp_unreachable();
}
[[nodiscard]] static sys_seconds
__rule_to_sys_seconds(seconds __stdoff, seconds __save, const __tz::__rule& __rule, year __year) {
year_month_day __ymd = chrono::__to_year_month_day(__year, __rule.__in, __rule.__on);
seconds __at = chrono::__at_to_seconds(__stdoff, __save, __rule);
return chrono::__to_sys_seconds(__ymd, __at);
}
// Returns the first rule after __time.
// Note that a rule can be "active" in multiple years, this may result in an
// infinite loop where the same rule is returned every time, use __current to
// guard against that.
//
// When no next rule exists the returned time will be sys_seconds::max(). This
// can happen in practice. For example,
//
// R So 1945 o - May 24 2 2 M
// R So 1945 o - S 24 3 1 S
// R So 1945 o - N 18 2s 0 -
//
// Has 3 rules that are all only active in 1945.
[[nodiscard]] static pair<sys_seconds, vector<__tz::__rule>::const_iterator>
__next_rule(sys_seconds __time,
seconds __stdoff,
seconds __save,
const vector<__tz::__rule>& __rules,
vector<__tz::__rule>::const_iterator __current) {
year __year = year_month_day{chrono::floor<days>(__time)}.year();
// Note it would probably be better to store the pairs in a vector and then
// use min() to get the smallest element
map<sys_seconds, vector<__tz::__rule>::const_iterator> __candidates;
// Note this evaluates all rules which is a waste of effort; when the entries
// are beyond the current year's "next year" (where "next year" is not always
// year + 1) the algorithm should end.
for (auto __it = __rules.begin(); __it != __rules.end(); ++__it) {
for (year __y = __it->__from; __y <= __it->__to; ++__y) {
// Adding the current entry for the current year may lead to infinite
// loops due to the SAVE adjustment. Skip these entries.
if (__y == __year && __it == __current)
continue;
sys_seconds __t = chrono::__rule_to_sys_seconds(__stdoff, __save, *__it, __y);
if (__t <= __time)
continue;
_LIBCPP_ASSERT_ARGUMENT_WITHIN_DOMAIN(!__candidates.contains(__t), "duplicated rule");
__candidates[__t] = __it;
break;
}
}
if (!__candidates.empty()) [[likely]] {
auto __it = __candidates.begin();
// When no rule is selected the time before the first rule and the first rule
// should not be merged.
if (__time == sys_seconds::min())
return *__it;
// There can be two constitutive rules that are the same. For example,
// Hong Kong
//
// R HK 1973 o - D 30 3:30 1 S (R1)
// R HK 1965 1976 - Ap Su>=16 3:30 1 S (R2)
//
// 1973-12-29 19:30:00 R1 becomes active.
// 1974-04-20 18:30:00 R2 becomes active.
// Both rules have a SAVE of 1 hour and LETTERS are S for both of them.
while (__it != __candidates.end()) {
if (__current->__save.__time != __it->second->__save.__time || __current->__letters != __it->second->__letters)
return *__it;
++__it;
}
}
return {sys_seconds::max(), __rules.end()};
}
// Returns the first rule of a set of rules.
// This is not always the first of the listed rules. For example
// R Sa 2008 2009 - Mar Su>=8 0 0 -
// R Sa 2007 2008 - O Su>=8 0 1 -
// The transition in October 2007 happens before the transition in March 2008.
[[nodiscard]] static vector<__tz::__rule>::const_iterator
__first_rule(seconds __stdoff, const vector<__tz::__rule>& __rules) {
return chrono::__next_rule(sys_seconds::min(), __stdoff, 0s, __rules, __rules.end()).second;
}
[[nodiscard]] static __sys_info_result __get_sys_info_rule(
sys_seconds __time,
sys_seconds __continuation_begin,
const __tz::__continuation& __continuation,
const vector<__tz::__rule>& __rules) {
auto __rule = chrono::__first_rule(__continuation.__stdoff, __rules);
_LIBCPP_ASSERT_ARGUMENT_WITHIN_DOMAIN(__rule != __rules.end(), "the set of rules has no first rule");
// Avoid selecting a time before the start of the continuation
__time = std::max(__time, __continuation_begin);
sys_seconds __rule_begin = chrono::__from_to_sys_seconds(__continuation.__stdoff, *__rule);
// The time sought is very likely inside the current rule.
// When the continuation's UNTIL uses the local clock there are edge cases
// where this is not true.
//
// Start to walk the rules to find the proper one.
//
// For now we just walk all the rules TODO TZDB investigate whether a smarter
// algorithm would work.
auto __next = chrono::__next_rule(__rule_begin, __continuation.__stdoff, __rule->__save.__time, __rules, __rule);
// Ignore small steps, this happens with America/Punta_Arenas for the
// transition
// -4:42:46 - SMT 1927 S
// -5 x -05/-04 1932 S
// ...
//
// R x 1927 1931 - S 1 0 1 -
// R x 1928 1932 - Ap 1 0 0 -
//
// America/Punta_Arenas Thu Sep 1 04:42:45 1927 UT = Thu Sep 1 00:42:45 1927 -04 isdst=1 gmtoff=-14400
// America/Punta_Arenas Sun Apr 1 03:59:59 1928 UT = Sat Mar 31 23:59:59 1928 -04 isdst=1 gmtoff=-14400
// America/Punta_Arenas Sun Apr 1 04:00:00 1928 UT = Sat Mar 31 23:00:00 1928 -05 isdst=0 gmtoff=-18000
//
// Without this there will be a transition
// [1927-09-01 04:42:45, 1927-09-01 05:00:00) -05:00:00 0min -05
if (sys_seconds __begin = __rule->__save.__time != 0s ? __rule_begin : __next.first; __time < __begin) {
if (__continuation_begin == sys_seconds::min() || __begin - __continuation_begin > 12h)
return __sys_info{__get_sys_info_before_first_rule(
__continuation_begin, __rule_begin, __next.first, __continuation, __rules, __rule),
false};
// Europe/Berlin
// 1 c CE%sT 1945 May 24 2 (C1)
// 1 So CE%sT 1946 (C2)
//
// R c 1944 1945 - Ap M>=1 2s 1 S (R1)
//
// R So 1945 o - May 24 2 2 M (R2)
//
// When C2 becomes active the time would be before the first rule R2,
// giving a 1 hour sys_info.
seconds __save = __rule->__save.__time;
__named_rule_until __continuation_end{__continuation};
sys_seconds __sys_info_end = std::min(__continuation_end(__save), __next.first);
return __sys_info{
sys_info{__continuation_begin,
__sys_info_end,
__continuation.__stdoff + __save,
chrono::duration_cast<minutes>(__save),
chrono::__format(__continuation, __rule->__letters, __save)},
__sys_info_end == __continuation_end(__save)};
}
// See above for America/Asuncion
if (__rule->__save.__time == 0s && __time < __next.first) {
return __sys_info{
sys_info{__continuation_begin,
__next.first,
__continuation.__stdoff,
0min,
chrono::__format(__continuation, __rule->__letters, 0s)},
false};
}
if (__rule->__save.__time != 0s) {
// another fix for America/Punta_Arenas when not at the start of the
// sys_info object.
seconds __save = __rule->__save.__time;
if (__continuation_begin >= __rule_begin - __save && __time < __next.first) {
return __sys_info{
sys_info{__continuation_begin,
__next.first,
__continuation.__stdoff + __save,
chrono::duration_cast<minutes>(__save),
chrono::__format(__continuation, __rule->__letters, __save)},
false};
}
}
__named_rule_until __continuation_end{__continuation};
while (__next.second != __rules.end()) {
#ifdef PRINT
std::print(
stderr,
"Rule for {}: [{}, {}) off={} save={} duration={}\n",
__time,
__rule_begin,
__next.first,
__continuation.__stdoff,
__rule->__save.__time,
__next.first - __rule_begin);
#endif
sys_seconds __end = __continuation_end(__rule->__save.__time);
sys_seconds __sys_info_begin = std::max(__continuation_begin, __rule_begin);
sys_seconds __sys_info_end = std::min(__end, __next.first);
seconds __diff = chrono::abs(__sys_info_end - __sys_info_begin);
if (__diff < 12h) {
// Z America/Argentina/Buenos_Aires -3:53:48 - LMT 1894 O 31
// -4:16:48 - CMT 1920 May
// -4 - -04 1930 D
// -4 A -04/-03 1969 O 5
// -3 A -03/-02 1999 O 3
// -4 A -04/-03 2000 Mar 3
// ...
//
// ...
// R A 1989 1992 - O Su>=15 0 1 -
// R A 1999 o - O Su>=1 0 1 -
// R A 2000 o - Mar 3 0 0 -
// R A 2007 o - D 30 0 1 -
// ...
// The 1999 switch uses the same rule, but with a different stdoff.
// R A 1999 o - O Su>=1 0 1 -
// stdoff -3 -> 1999-10-03 03:00:00
// stdoff -4 -> 1999-10-03 04:00:00
// This generates an invalid entry and this is evaluated as a transition.
// Looking at the zdump like output in libc++ this generates jumps in
// the UTC time.
__rule = __next.second;
__next = __next_rule(__next.first, __continuation.__stdoff, __rule->__save.__time, __rules, __rule);
__end = __continuation_end(__rule->__save.__time);
__sys_info_end = std::min(__end, __next.first);
}
if ((__time >= __rule_begin && __time < __next.first) || __next.first >= __end) {
__sys_info_begin = std::max(__continuation_begin, __rule_begin);
__sys_info_end = std::min(__end, __next.first);
return __sys_info{
sys_info{__sys_info_begin,
__sys_info_end,
__continuation.__stdoff + __rule->__save.__time,
chrono::duration_cast<minutes>(__rule->__save.__time),
chrono::__format(__continuation, __rule->__letters, __rule->__save.__time)},
__sys_info_end == __end};
}
__rule_begin = __next.first;
__rule = __next.second;
__next = __next_rule(__rule_begin, __continuation.__stdoff, __rule->__save.__time, __rules, __rule);
}
return __sys_info{
sys_info{std::max(__continuation_begin, __rule_begin),
__continuation_end(__rule->__save.__time),
__continuation.__stdoff + __rule->__save.__time,
chrono::duration_cast<minutes>(__rule->__save.__time),
chrono::__format(__continuation, __rule->__letters, __rule->__save.__time)},
true};
}
[[nodiscard]] static __sys_info_result __get_sys_info_basic(
sys_seconds __time, sys_seconds __continuation_begin, const __tz::__continuation& __continuation, seconds __save) {
sys_seconds __continuation_end = chrono::__until_to_sys_seconds(__continuation);
return __sys_info{
sys_info{__continuation_begin,
__continuation_end,
__continuation.__stdoff + __save,
chrono::duration_cast<minutes>(__save),
__continuation.__format},
true};
}
[[nodiscard]] static __sys_info_result
__get_sys_info(sys_seconds __time,
sys_seconds __continuation_begin,
const __tz::__continuation& __continuation,
const __tz::__rules_storage_type& __rules_db) {
return std::visit(
[&](const auto& __value) {
using _Tp = decay_t<decltype(__value)>;
if constexpr (same_as<_Tp, std::string>)
return chrono::__get_sys_info_rule(
__time, __continuation_begin, __continuation, __get_rules(__rules_db, __value));
else if constexpr (same_as<_Tp, monostate>)
return chrono::__get_sys_info_basic(__time, __continuation_begin, __continuation, chrono::seconds(0));
else if constexpr (same_as<_Tp, __tz::__save>)
return chrono::__get_sys_info_basic(__time, __continuation_begin, __continuation, __value.__time);
else
static_assert(sizeof(_Tp) == 0); // TODO TZDB static_assert(false); after droping clang-16 support
std::__libcpp_unreachable();
},
__continuation.__rules);
}
// The transition from one continuation to the next continuation may result in
// two constitutive continuations with the same "offset" information.
// [time.zone.info.sys]/3
// The begin and end data members indicate that, for the associated time_zone
// and time_point, the offset and abbrev are in effect in the range
// [begin, end). This information can be used to efficiently iterate the
// transitions of a time_zone.
//
// Note that this does considers a change in the SAVE field not to be a
// different sys_info, zdump does consider this different.
// LWG XXXX The sys_info range should be affected by save
// matches the behaviour of the Standard and zdump.
//
// Iff the "offsets" are the same '__current.__end' is replaced with
// '__next.__end', which effectively merges the two objects in one object. The
// function returns true if a merge occurred.
[[nodiscard]] bool __merge_continuation(sys_info& __current, const sys_info& __next) {
if (__current.end != __next.begin)
return false;
if (__current.offset != __next.offset || __current.abbrev != __next.abbrev || __current.save != __next.save)
return false;
__current.end = __next.end;
return true;
}
//===----------------------------------------------------------------------===//
// Public API
//===----------------------------------------------------------------------===//
[[nodiscard]] _LIBCPP_EXPORTED_FROM_ABI time_zone time_zone::__create(unique_ptr<time_zone::__impl>&& __p) {
_LIBCPP_ASSERT_NON_NULL(__p != nullptr, "initialized time_zone without a valid pimpl object");
time_zone result;
result.__impl_ = std::move(__p);
return result;
}
_LIBCPP_EXPORTED_FROM_ABI time_zone::~time_zone() = default;
[[nodiscard]] _LIBCPP_EXPORTED_FROM_ABI string_view time_zone::__name() const noexcept { return __impl_->__name(); }
[[nodiscard]] _LIBCPP_AVAILABILITY_TZDB _LIBCPP_EXPORTED_FROM_ABI sys_info
time_zone::__get_info(sys_seconds __time) const {
optional<sys_info> __result;
bool __valid_result = false; // true iff __result.has_value() is true and
// __result.begin <= __time < __result.end is true.
bool __can_merge = false;
sys_seconds __continuation_begin = sys_seconds::min();
// Iterates over the Zone entry and its continuations. Internally the Zone
// entry is split in a Zone information and the first continuation. The last
// continuation has no UNTIL field. This means the loop should always find a
// continuation.
//
// For more information on background of zone information please consult the
// following information
// [zic manual](https://www.man7.org/linux/man-pages/man8/zic.8.html)
// [tz source info](https://data.iana.org/time-zones/tz-how-to.html)
// On POSIX systems the zdump tool can be useful:
// zdump -v Asia/Hong_Kong
// Gives all transitions in the Hong Kong time zone.
//
// During iteration the result for the current continuation is returned. If
// no continuation is applicable it will return the end time as "error". When
// two continuations are contiguous and contain the "same" information these
// ranges are merged as one range.
// The merging requires keeping any result that occurs before __time,
// likewise when a valid result is found the algorithm needs to test the next
// continuation to see whether it can be merged. For example, Africa/Ceuta
// Continuations
// 0 s WE%sT 1929 (C1)
// 0 - WET 1967 (C2)
// 0 Sp WE%sT 1984 Mar 16 (C3)
//
// Rules
// R s 1926 1929 - O Sa>=1 24s 0 - (R1)
//
// R Sp 1967 o - Jun 3 12 1 S (R2)
//
// The rule R1 is the last rule used in C1. The rule R2 is the first rule in
// C3. Since R2 is the first rule this means when a continuation uses this
// rule its value prior to R2 will be SAVE 0 LETTERS of the first entry with a
// SAVE of 0, in this case WET.
// This gives the following changes in the information.
// 1928-10-07 00:00:00 C1 R1 becomes active: offset 0 save 0 abbrev WET
// 1929-01-01 00:00:00 C2 becomes active: offset 0 save 0 abbrev WET
// 1967-01-01 00:00:00 C3 becomes active: offset 0 save 0 abbrev WET
// 1967-06-03 12:00:00 C3 R2 becomes active: offset 0 save 1 abbrev WEST
//
// The first 3 entries are contiguous and contain the same information, this
// means the period [1928-10-07 00:00:00, 1967-06-03 12:00:00) should be
// returned in one sys_info object.
const auto& __continuations = __impl_->__continuations();
const __tz::__rules_storage_type& __rules_db = __impl_->__rules_db();
for (auto __it = __continuations.begin(); __it != __continuations.end(); ++__it) {
const auto& __continuation = *__it;
__sys_info_result __sys_info = chrono::__get_sys_info(__time, __continuation_begin, __continuation, __rules_db);
if (__sys_info) {
_LIBCPP_ASSERT_ARGUMENT_WITHIN_DOMAIN(
__sys_info->__info.begin < __sys_info->__info.end, "invalid sys_info range");
// Filters out dummy entries
// Z America/Argentina/Buenos_Aires -3:53:48 - LMT 1894 O 31
// ...
// -4 A -04/-03 2000 Mar 3 (C1)
// -3 A -03/-02 (C2)
//
// ...
// R A 2000 o - Mar 3 0 0 -
// R A 2007 o - D 30 0 1 -
// ...
//
// This results in an entry
// [2000-03-03 03:00:00, 2000-03-03 04:00:00) -10800s 60min -03
// for [C1 & R1, C1, R2) which due to the end of the continuation is an
// one hour "sys_info". Instead the entry should be ignored and replaced
// by [C2 & R1, C2 & R2) which is the proper range
// "[2000-03-03 03:00:00, 2007-12-30 03:00:00) -02:00:00 60min -02
if (std::holds_alternative<string>(__continuation.__rules) && __sys_info->__can_merge &&
__sys_info->__info.begin + 12h > __sys_info->__info.end) {
__continuation_begin = __sys_info->__info.begin;
continue;
}
if (!__result) {
// First entry found, always keep it.
__result = __sys_info->__info;
__valid_result = __time >= __result->begin && __time < __result->end;
__can_merge = __sys_info->__can_merge;
} else if (__can_merge && chrono::__merge_continuation(*__result, __sys_info->__info)) {
// The results are merged, update the result state. This may
// "overwrite" a valid sys_info object with another valid sys_info
// object.
__valid_result = __time >= __result->begin && __time < __result->end;
__can_merge = __sys_info->__can_merge;
} else {
// Here things get interesting:
// For example, America/Argentina/San_Luis
//
// -3 A -03/-02 2008 Ja 21 (C1)
// -4 Sa -04/-03 2009 O 11 (C2)
//
// R A 2007 o - D 30 0 1 - (R1)
//
// R Sa 2007 2008 - O Su>=8 0 1 - (R2)
//
// Based on C1 & R1 the end time of C1 is 2008-01-21 03:00:00
// Based on C2 & R2 the end time of C1 is 2008-01-21 02:00:00
// In this case the earlier time is the real time of the transition.
// However the algorithm used gives 2008-01-21 03:00:00.
//
// So we need to calculate the previous UNTIL in the current context and
// see whether it's earlier.
// The results could not be merged.
// - When we have a valid result that result is the final result.
// - Otherwise the result we had is before __time and the result we got
// is at a later time (possibly valid). This result is always better
// than the previous result.
if (__valid_result) {
return *__result;
} else {
_LIBCPP_ASSERT_ARGUMENT_WITHIN_DOMAIN(
__it != __continuations.begin(), "the first rule should always seed the result");
const auto& __last = *(__it - 1);
if (std::holds_alternative<string>(__last.__rules)) {
// Europe/Berlin
// 1 c CE%sT 1945 May 24 2 (C1)
// 1 So CE%sT 1946 (C2)
//
// R c 1944 1945 - Ap M>=1 2s 1 S (R1)
//
// R So 1945 o - May 24 2 2 M (R2)
//
// When C2 becomes active the time would be before the first rule R2,
// giving a 1 hour sys_info. This is not valid and the results need
// merging.
if (__result->end != __sys_info->__info.begin) {
// When the UTC gap between the rules is due to the change of
// offsets adjust the new time to remove the gap.
sys_seconds __end = __result->end - __result->offset;
sys_seconds __begin = __sys_info->__info.begin - __sys_info->__info.offset;
if (__end == __begin) {
__sys_info->__info.begin = __result->end;
}
}
}
__result = __sys_info->__info;
__valid_result = __time >= __result->begin && __time < __result->end;
__can_merge = __sys_info->__can_merge;
}
}
__continuation_begin = __result->end;
} else {
__continuation_begin = __sys_info.error();
}
}
if (__valid_result)
return *__result;
std::__throw_runtime_error("tzdb: corrupt db");
}
// Is the "__local_time" present in "__first" and "__second". If so the
// local_info has an ambiguous result.
[[nodiscard]] static bool
__is_ambiguous(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};
return __local_time < __end_first && __local_time >= __begin_second;
}
// Determines the result of the "__local_time". This expects the object
// "__first" to be earlier in time than "__second".
[[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
* |------------//----------|
* |---------//--------------|
* |-------------
* ~~ ^^
*
* 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 not have 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 that, determine the offset and 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 found in the sys_info, the local time can be
// converted to a system time. This resulting time can be in the following
// locations of the sys_info:
//
// |---------//--------------|
// 1 2.1 2.2 2.3 3
//
// 1. The estimate is before the returned sys_info object.
// The result is either non-existent or unique in the previous sys_info.
// 2. The estimate is in the sys_info object
// - If the sys_info begin is not sys_seconds::min(), then it might be at
// 2.1 and could be ambiguous with the previous or unique.
// - If sys_info end is not sys_seconds::max(), then it might be at 2.3
// and could be ambiguous with the next or unique.
// - Else it is at 2.2 and always unique. This case happens when a
// time zone has no transitions. For example, UTC or GMT+1.
// 3. The estimate is after the returned sys_info object.
// The result is either non-existent or unique in the next sys_info.
//
// There is no specification where the "middle" starts. Similar issues can
// happen when sys_info objects are "short", then "unique in the next" could
// become "ambiguous in the next and the one following". Theoretically there
// is the option of the following time-line
//
// |------------|
// |----|
// |-----------------|
//
// However the local_info object only has 2 sys_info objects, so this option
// is not tested.
sys_seconds __sys_time{__local_seconds - __info.offset};
if (__sys_time < __info.begin)
// Case 1 before __info
return chrono::__get_info(__local_time, __get_info(__info.begin - 1s), __info);
if (__sys_time >= __info.end)
// Case 3 after __info
return chrono::__get_info(__local_time, __info, __get_info(__info.end));
// Case 2 in __info
if (__info.begin != sys_seconds::min()) {
// Case 2.1 Not at the beginning, when not ambiguous the result should test
// case 2.3.
sys_info __prev = __get_info(__info.begin - 1s);
if (__is_ambiguous(__local_time, __prev, __info))
return {local_info::ambiguous, __prev, __info};
}
if (__info.end == sys_seconds::max())
// At the end so it's case 2.2
return {local_info::unique, __info, sys_info{}};
// This tests case 2.2 or case 2.3.
return chrono::__get_info(__local_time, __info, __get_info(__info.end));
}
} // namespace chrono
_LIBCPP_END_NAMESPACE_STD
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