Hello,The attached patch implements P2592, adding std::hash specializations for std::chrono classes.
One aspect I'm quite unhappy with is the hash combiner I've used. I'm not sure if there's some longer-term goal for libstdc++ here -- would you prefer to roll something à la Boost.HashCombine / P0814?
Not only it's likely to be cheaper, but it would also be more constexpr-friendly, in preparation of constexpr std::hash (P3372).
As usual, any feedback is appreciated :) Thank you, -- Giuseppe D'Angelo
From 7f1c88139c2b906982cb036f39bfa80db122c7af Mon Sep 17 00:00:00 2001
From: Giuseppe D'Angelo <giuseppe.dang...@kdab.com>
Date: Wed, 4 Sep 2024 12:57:51 +0200
Subject: [PATCH] libstdc++: hashing support for chrono value classes (P2592R2)
This commit implements [time.hash], added by P2592 for C++26.
The implementation of the various hash specializations is
mostly straightforward:
* duration hashes its representation (not the period);
* time_point hashes its duration;
* the calendaring classes (year, month, day, etc.) hash their
values;
* zoned_time hashes the time zone pointer and its time point.
There are however a couple of challenges:
* The noexcept specifications for hashing duration, time_point,
zoned_time are slightly more convoluted than expected, as
their getters are noexcept(false) (e.g. calling count() on a
duration will copy the representation and that may throw);
* [time.duration] says that "Rep shall be an arithmetic type or a
class emulating an arithmetic type". Technically speaking, this
means that `const int` is a valid Rep; but we can't use
hash<const int>.
I'm not sure if this is deliberate or not (cf. LWG951, LWG953),
but I've decided to support it nonetheless.
* zoned_time and the calendar classes that combine several
parts (e.g. month_day) need a hash combiner. The one
available in _Hash_impl works on objects representations,
not values, and given the nature of the calendar classes
I'm very afraid that I may accidentally be hashing padding
bits. Therefore, I've added a helper convenience combiner.
libstdc++-v3/ChangeLog:
* include/bits/functional_hash.h: Add a convenience hash
combiner.
* include/bits/version.def: Bump the feature-testing macro.
* include/bits/version.h: Regenerate.
* include/std/chrono: Add std::hash specializations for the
value classes in namespace chrono.
* testsuite/std/time/hash.cc: New test.
Signed-off-by: Giuseppe D'Angelo <giuseppe.dang...@kdab.com>
---
libstdc++-v3/include/bits/functional_hash.h | 31 ++
libstdc++-v3/include/bits/version.def | 6 +
libstdc++-v3/include/bits/version.h | 7 +-
libstdc++-v3/include/std/chrono | 299 ++++++++++++++++++++
libstdc++-v3/testsuite/std/time/hash.cc | 225 +++++++++++++++
5 files changed, 567 insertions(+), 1 deletion(-)
create mode 100644 libstdc++-v3/testsuite/std/time/hash.cc
diff --git a/libstdc++-v3/include/bits/functional_hash.h b/libstdc++-v3/include/bits/functional_hash.h
index 3626ebe816b..c0f82601b4b 100644
--- a/libstdc++-v3/include/bits/functional_hash.h
+++ b/libstdc++-v3/include/bits/functional_hash.h
@@ -235,6 +235,37 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
{ return hash(&__val, sizeof(__val), __hash); }
};
+#if __cplusplus >= 201103L // C++11
+ // A convenience hash combiner
+ struct _Hash_combiner
+ {
+ static void __hash_combine(size_t&) {}
+
+ template<typename _Arg, typename... _Args>
+ static void
+ __hash_combine(size_t& __result,
+ const _Arg& __arg,
+ const _Args&... __args)
+ {
+ const size_t __arg_hash = hash<_Arg>{}(__arg);
+ __result = _Hash_impl::__hash_combine(__arg_hash, __result);
+ __hash_combine(__result, __args...);
+ }
+
+ static size_t __hash()
+ { return 0; }
+
+ template<typename _Arg, typename... _Args>
+ static size_t __hash(const _Arg& __arg, const _Args&... __args)
+ {
+ const size_t __arg_hash = hash<_Arg>{}(__arg);
+ size_t __result = _Hash_impl::hash(__arg_hash);
+ __hash_combine(__result, __args...);
+ return __result;
+ }
+ };
+#endif // C++11
+
/// Specialization for float.
template<>
struct hash<float> : public __hash_base<size_t, float>
diff --git a/libstdc++-v3/include/bits/version.def b/libstdc++-v3/include/bits/version.def
index 59b028c44af..2a2bbf54b3f 100644
--- a/libstdc++-v3/include/bits/version.def
+++ b/libstdc++-v3/include/bits/version.def
@@ -575,6 +575,12 @@ ftms = {
ftms = {
name = chrono;
+ values = {
+ v = 202306;
+ cxxmin = 26;
+ hosted = yes;
+ cxx11abi = yes;
+ };
values = {
v = 201907;
cxxmin = 20;
diff --git a/libstdc++-v3/include/bits/version.h b/libstdc++-v3/include/bits/version.h
index e465131d99b..c75cb009ada 100644
--- a/libstdc++-v3/include/bits/version.h
+++ b/libstdc++-v3/include/bits/version.h
@@ -644,7 +644,12 @@
#undef __glibcxx_want_boyer_moore_searcher
#if !defined(__cpp_lib_chrono)
-# if (__cplusplus >= 202002L) && _GLIBCXX_USE_CXX11_ABI && _GLIBCXX_HOSTED
+# if (__cplusplus > 202302L) && _GLIBCXX_USE_CXX11_ABI && _GLIBCXX_HOSTED
+# define __glibcxx_chrono 202306L
+# if defined(__glibcxx_want_all) || defined(__glibcxx_want_chrono)
+# define __cpp_lib_chrono 202306L
+# endif
+# elif (__cplusplus >= 202002L) && _GLIBCXX_USE_CXX11_ABI && _GLIBCXX_HOSTED
# define __glibcxx_chrono 201907L
# if defined(__glibcxx_want_all) || defined(__glibcxx_want_chrono)
# define __cpp_lib_chrono 201907L
diff --git a/libstdc++-v3/include/std/chrono b/libstdc++-v3/include/std/chrono
index 7ffa5360728..8c6b173bc5d 100644
--- a/libstdc++-v3/include/std/chrono
+++ b/libstdc++-v3/include/std/chrono
@@ -50,6 +50,10 @@
# include <bits/unique_ptr.h>
#endif
+#if __cplusplus > 202302L
+# include <bits/functional_hash.h>
+#endif
+
#define __glibcxx_want_chrono
#define __glibcxx_want_chrono_udls
#include <bits/version.h>
@@ -3329,6 +3333,301 @@ namespace __detail
#endif // C++20
} // namespace chrono
+#if __glibcxx_chrono >= 202306 // C++26
+ // Hash support [time.hash]
+
+ // duration
+ template<typename _Rep, typename _Period,
+ typename _ActualRep = remove_cv_t<_Rep>,
+ bool = __poison_hash<_ActualRep>::__enable_hash_call>
+ struct __chrono_duration_hash_base
+ {
+ size_t
+ operator()(const chrono::duration<_Rep, _Period>& __val) const
+ noexcept(
+ is_nothrow_copy_constructible_v<_Rep> &&
+ noexcept(hash<_ActualRep>{}(std::declval<_Rep>()))
+ )
+ {
+ return hash<_ActualRep>{}(__val.count());
+ }
+ };
+
+ template<typename _Rep, typename _Period, typename _ActualRep>
+ struct __chrono_duration_hash_base<_Rep, _Period, _ActualRep, false>
+ {};
+
+ template<typename _Rep, typename _Period>
+ struct hash<chrono::duration<_Rep, _Period>>
+ : private __poison_hash<remove_cv_t<_Rep>>,
+ public __chrono_duration_hash_base<_Rep, _Period>
+ {
+ using result_type [[__deprecated__]] = size_t;
+ using argument_type [[__deprecated__]] = chrono::duration<_Rep, _Period>;
+ };
+
+ template<typename _Rep, typename _Period>
+ struct __is_fast_hash<hash<chrono::duration<_Rep, _Period>>>
+ : __is_fast_hash<hash<_Rep>>
+ {};
+
+ // time_point
+ template<typename _Clock, typename _Dur,
+ bool = __poison_hash<_Dur>::__enable_hash_call>
+ struct __chrono_time_point_hash_base
+ {
+ size_t
+ operator()(const chrono::time_point<_Clock, _Dur>& __val) const
+ noexcept(
+ is_nothrow_copy_constructible_v<_Dur> &&
+ noexcept(hash<_Dur>{}(std::declval<_Dur>()))
+ )
+ {
+ return hash<_Dur>{}(__val.time_since_epoch());
+ }
+ };
+
+ template<typename _Clock, typename _Dur>
+ struct __chrono_time_point_hash_base<_Clock, _Dur, false>
+ {};
+
+ template<typename _Clock, typename _Dur>
+ struct hash<chrono::time_point<_Clock, _Dur>>
+ : private __poison_hash<_Dur>,
+ public __chrono_time_point_hash_base<_Clock, _Dur>
+ {
+ using result_type [[__deprecated__]] = size_t;
+ using argument_type [[__deprecated__]] = chrono::time_point<_Clock, _Dur>;
+ };
+
+ template<typename _Clock, typename _Dur>
+ struct __is_fast_hash<hash<chrono::time_point<_Clock, _Dur>>>
+ : __is_fast_hash<hash<_Dur>>
+ {};
+
+ // day
+ template<>
+ struct hash<chrono::day>
+ : public __hash_base<size_t, chrono::day>
+ {
+ size_t operator()(chrono::day __val) const noexcept
+ { return static_cast<unsigned>(__val); }
+ };
+
+ // month
+ template<>
+ struct hash<chrono::month>
+ : public __hash_base<size_t, chrono::month>
+ {
+ size_t operator()(chrono::month __val) const noexcept
+ { return static_cast<unsigned>(__val); }
+ };
+
+ // year
+ template<>
+ struct hash<chrono::year>
+ : public __hash_base<size_t, chrono::year>
+ {
+ size_t operator()(chrono::year __val) const noexcept
+ {
+ const int __tmp = static_cast<int>(__val);
+ return static_cast<size_t>(__tmp);
+ }
+ };
+
+ // weekday
+ template<>
+ struct hash<chrono::weekday>
+ : public __hash_base<size_t, chrono::weekday>
+ {
+ size_t operator()(chrono::weekday __val) const noexcept
+ { return static_cast<size_t>(__val.c_encoding()); }
+ };
+
+ // weekday_indexed
+ template<>
+ struct hash<chrono::weekday_indexed>
+ : public __hash_base<size_t, chrono::weekday_indexed>
+ {
+ size_t operator()(chrono::weekday_indexed __val) const noexcept
+ {
+ return _Hash_combiner::__hash(__val.weekday(), __val.index());
+ }
+ };
+
+ // weekday_last
+ template<>
+ struct hash<chrono::weekday_last>
+ : public __hash_base<size_t, chrono::weekday_last>
+ {
+ size_t operator()(chrono::weekday_last __val) const noexcept
+ { return static_cast<size_t>(__val.weekday().c_encoding()); }
+ };
+
+ // month_day
+ template<>
+ struct hash<chrono::month_day>
+ : public __hash_base<size_t, chrono::month_day>
+ {
+ size_t operator()(chrono::month_day __val) const noexcept
+ {
+ return _Hash_combiner::__hash(__val.month(), __val.day());
+ }
+ };
+
+ // month_day_last
+ template<>
+ struct hash<chrono::month_day_last>
+ : public __hash_base<size_t, chrono::month_day_last>
+ {
+ size_t operator()(chrono::month_day_last __val) const noexcept
+ { return static_cast<unsigned>(__val.month()); }
+ };
+
+ // month_weekday
+ template<>
+ struct hash<chrono::month_weekday>
+ : public __hash_base<size_t, chrono::month_weekday>
+ {
+ size_t operator()(chrono::month_weekday __val) const noexcept
+ {
+ return _Hash_combiner::__hash(__val.month(), __val.weekday_indexed());
+ }
+ };
+
+ // month_weekday_last
+ template<>
+ struct hash<chrono::month_weekday_last>
+ : public __hash_base<size_t, chrono::month_weekday_last>
+ {
+ size_t
+ operator()(chrono::month_weekday_last __val) const noexcept
+ {
+ return _Hash_combiner::__hash(__val.month(), __val.weekday_last());
+ }
+ };
+
+ // year_month
+ template<>
+ struct hash<chrono::year_month>
+ : public __hash_base<size_t, chrono::year_month>
+ {
+ size_t operator()(chrono::year_month __val) const noexcept
+ {
+ return _Hash_combiner::__hash(__val.year(), __val.month());
+ }
+ };
+
+ // year_month_day
+ template<>
+ struct hash<chrono::year_month_day>
+ : public __hash_base<size_t, chrono::year_month_day>
+ {
+ size_t operator()(chrono::year_month_day __val) const noexcept
+ {
+ return _Hash_combiner::__hash(__val.year(),
+ __val.month(),
+ __val.day());
+ }
+ };
+
+ // year_month_day_last
+ template<>
+ struct hash<chrono::year_month_day_last>
+ : public __hash_base<size_t, chrono::year_month_day_last>
+ {
+ size_t
+ operator()(chrono::year_month_day_last __val) const noexcept
+ {
+ return _Hash_combiner::__hash(__val.year(),
+ __val.month_day_last());
+ }
+ };
+
+ // year_month_weekday
+ template<>
+ struct hash<chrono::year_month_weekday>
+ : public __hash_base<size_t, chrono::year_month_weekday>
+ {
+ size_t operator()(chrono::year_month_weekday __val) const noexcept
+ {
+ return _Hash_combiner::__hash(__val.year(),
+ __val.month(),
+ __val.weekday_indexed());
+ }
+ };
+
+ // year_month_weekday_last
+ template<>
+ struct hash<chrono::year_month_weekday_last>
+ : public __hash_base<size_t, chrono::year_month_weekday_last>
+ {
+ size_t
+ operator()(chrono::year_month_weekday_last __val) const noexcept
+ {
+ return _Hash_combiner::__hash(__val.year(),
+ __val.month(),
+ __val.weekday_last());
+ }
+ };
+
+ // zoned_time
+ template<typename _Duration, typename _TimeZonePtr,
+ typename _ActualDuration =
+ typename chrono::zoned_time<_Duration, _TimeZonePtr>::duration,
+ bool = (__poison_hash<_ActualDuration>::__enable_hash_call &&
+ __poison_hash<_TimeZonePtr>::__enable_hash_call)>
+ struct __chrono_zoned_time_hash_base
+ {
+ size_t
+ operator()
+ (const chrono::zoned_time<_Duration, _TimeZonePtr>& __val)
+ const
+ noexcept(
+ is_nothrow_copy_constructible_v<_ActualDuration> &&
+ noexcept(hash<_ActualDuration>{}(std::declval<_ActualDuration>())) &&
+ is_nothrow_copy_constructible_v<_TimeZonePtr> &&
+ noexcept(hash<_TimeZonePtr>{}(std::declval<_TimeZonePtr>()))
+ )
+ {
+ return _Hash_combiner::__hash(__val.get_sys_time(),
+ __val.get_time_zone());
+ }
+ };
+
+ template<typename _Duration, typename _TimeZonePtr,
+ typename _ActualDuration>
+ struct __chrono_zoned_time_hash_base
+ <_Duration, _TimeZonePtr, _ActualDuration, false>
+ {};
+
+ template<typename _Duration, typename _TimeZonePtr>
+ struct hash<chrono::zoned_time<_Duration, _TimeZonePtr>>
+ : private __poison_hash<_Duration>,
+ private __poison_hash<_TimeZonePtr>,
+ public __chrono_zoned_time_hash_base<_Duration, _TimeZonePtr>
+ {
+ using result_type [[__deprecated__]] = size_t;
+ using argument_type [[__deprecated__]] =
+ chrono::zoned_time<_Duration, _TimeZonePtr>;
+ };
+
+ template<typename _Duration, typename _TimeZonePtr>
+ struct __is_fast_hash<hash<chrono::zoned_time<_Duration, _TimeZonePtr>>>
+ : bool_constant<__is_fast_hash<hash<_Duration>>::value &&
+ __is_fast_hash<hash<_TimeZonePtr>>::value>
+ {};
+
+ // leap_second
+ template<>
+ struct hash<chrono::leap_second>
+ : public __hash_base<size_t, chrono::leap_second>
+ {
+ size_t operator()(chrono::leap_second __val) const noexcept
+ { return hash<chrono::seconds>{}(__val.value()); }
+ };
+#endif // __glibcxx_chrono >= 202306
+
#if __cplusplus >= 202002L
inline namespace literals
{
diff --git a/libstdc++-v3/testsuite/std/time/hash.cc b/libstdc++-v3/testsuite/std/time/hash.cc
new file mode 100644
index 00000000000..bbc7699bf68
--- /dev/null
+++ b/libstdc++-v3/testsuite/std/time/hash.cc
@@ -0,0 +1,225 @@
+// { dg-do run { target c++26 } }
+// { dg-require-effective-target tzdb }
+
+#include <chrono>
+#include <unordered_set>
+#include <limits.h>
+#include <testsuite_hooks.h>
+
+#if !defined(__cpp_lib_chrono)
+#error "__cpp_lib_chrono not defined"
+#elif __cpp_lib_chrono < 202306L
+#error "Wrong value for __cpp_lib_chrono"
+#endif
+
+template <typename T>
+struct arithmetic_wrapper
+{
+ arithmetic_wrapper() = default;
+ arithmetic_wrapper(T t) : t(t) {}
+ friend bool operator==(arithmetic_wrapper, arithmetic_wrapper) = default;
+ T t;
+};
+
+template <typename T>
+struct std::hash<arithmetic_wrapper<T>>
+{
+ size_t operator()(arithmetic_wrapper<T> val) const noexcept
+ { return std::hash<T>{}(val.t); }
+};
+
+template <typename T>
+void test_unordered_set(const T& t)
+{
+ std::unordered_set<T> set;
+
+ set.insert(t);
+ VERIFY(set.size() == 1);
+ VERIFY(set.contains(t));
+
+ set.erase(t);
+ VERIFY(set.size() == 0);
+ VERIFY(!set.contains(t));
+}
+
+template <typename T>
+void test_hash(const T& t)
+{
+ static_assert(noexcept(std::hash<T>{}(t)));
+ test_unordered_set(t);
+}
+
+void test01()
+{
+ using namespace std::chrono;
+ using namespace std::literals::chrono_literals;
+
+ // duration
+ test_hash(-999s);
+ test_hash(1234ms);
+ test_hash(duration<double>(123.45));
+ using AWint = arithmetic_wrapper<int>;
+ test_hash(duration<AWint>(AWint(1234)));
+ using AWdouble = arithmetic_wrapper<double>;
+ test_hash(duration<AWdouble>(AWdouble(123.45)));
+
+ // time_point
+ test_hash(sys_seconds(1234s));
+ test_hash(sys_time<duration<double>>(duration<double>(123.45)));
+ test_hash(utc_seconds(1234s));
+ test_hash(local_days(days(1234)));
+ test_hash(system_clock::now());
+ test_hash(steady_clock::now());
+ test_hash(utc_clock::now());
+ test_hash(gps_clock::now());
+
+ // day
+ test_hash(1d);
+ test_hash(0d);
+ test_hash(255d);
+ test_hash(1234d);
+ test_hash(day(UINT_MAX));
+
+ // month
+ test_hash(January);
+ test_hash(September);
+ test_hash(month(0u));
+ test_hash(month(255u));
+ test_hash(month(1234u));
+ test_hash(month(UINT_MAX));
+
+ // year
+ test_hash(2024y);
+ test_hash(0y);
+ test_hash(year::min());
+ test_hash(year::max());
+ test_hash(year(INT_MAX));
+ test_hash(year(INT_MIN));
+
+ // weekday
+ test_hash(Monday);
+ test_hash(Thursday);
+ test_hash(weekday(255u));
+ test_hash(weekday(UINT_MAX));
+
+ // weekday_indexed
+ test_hash(Monday[0u]);
+ test_hash(Monday[7u]);
+ test_hash(Monday[1234u]);
+ test_hash(weekday(1234u)[0u]);
+
+ // weekday_last
+ test_hash(Monday[last]);
+ test_hash(Friday[last]);
+ test_hash(weekday(1234u)[last]);
+
+ // month_day
+ test_hash(March / 3);
+ test_hash(March / 31);
+ test_hash(February / 31);
+ test_hash(February / 1234);
+ test_hash(month(1234u) / 1);
+
+ // month_day_last
+ test_hash(March / last);
+ test_hash(month(1234u) / last);
+
+ // month_weekday
+ test_hash(March / Tuesday[2u]);
+ test_hash(month(1234u) / Tuesday[2u]);
+ test_hash(March / weekday(1234u)[2u]);
+ test_hash(March / Tuesday[1234u]);
+
+ // month_weekday_last
+ test_hash(April / Sunday[last]);
+ test_hash(month(1234u) / Tuesday[last]);
+ test_hash(April / weekday(1234u)[last]);
+
+ // year_month
+ test_hash(2024y / August);
+ test_hash(1'000'000y / August);
+ test_hash(2024y / month(1234u));
+
+ // year_month_day
+ test_hash(2024y / August / 31);
+ test_hash(-10y / March / 5);
+ test_hash(2024y / February / 31);
+ test_hash(1'000'000y / March / 5);
+ test_hash(2024y / month(1234u) / 5);
+ test_hash(2024y / March / 1234);
+
+ // year_month_day_last
+ test_hash(2024y / August / last);
+ test_hash(1'000'000y / August / last);
+ test_hash(2024y / month(1234u) / last);
+
+ // year_month_weekday
+ test_hash(2024y / August / Tuesday[2u]);
+ test_hash(-10y / August / Tuesday[2u]);
+ test_hash(1'000'000y / August / Tuesday[2u]);
+ test_hash(2024y / month(1234u) / Tuesday[2u]);
+ test_hash(2024y / August / weekday(1234u)[2u]);
+ test_hash(2024y / August / Tuesday[1234u]);
+
+ // year_month_weekday_last
+ test_hash(2024y / August / Tuesday[last]);
+ test_hash(-10y / August / Tuesday[last]);
+ test_hash(1'000'000y / August / Tuesday[last]);
+ test_hash(2024y / month(1234u) / Tuesday[last]);
+ test_hash(2024y / August / weekday(1234u)[last]);
+
+ // zoned_time
+ test_hash(zoned_seconds("Europe/Rome", sys_seconds(1234s)));
+ test_hash(zoned_time("Europe/Rome", system_clock::now()));
+
+ // leap_second
+ for (leap_second l : get_tzdb().leap_seconds)
+ test_hash(l);
+}
+
+void test02()
+{
+ using namespace std::chrono;
+ using namespace std::literals::chrono_literals;
+
+ {
+ std::unordered_set<milliseconds> set;
+ set.insert(2000ms);
+ VERIFY(set.contains(2000ms));
+ VERIFY(set.contains(2s));
+ VERIFY(!set.contains(1234ms));
+ VERIFY(!set.contains(1234s));
+ }
+ {
+ using TP = sys_time<milliseconds>;
+ std::unordered_set<TP> set;
+ set.insert(TP(2000ms));
+ VERIFY(set.contains(TP(2000ms)));
+ VERIFY(set.contains(sys_seconds(2s)));
+ VERIFY(!set.contains(TP(1234ms)));
+ VERIFY(!set.contains(sys_seconds(1234s)));
+ }
+}
+
+void test03()
+{
+ using namespace std::chrono;
+
+ const auto test = []<typename T>(const T& t)
+ {
+ static_assert(noexcept(std::hash<T>{}(t)));
+ };
+
+ test(duration<const int>(123));
+ test(duration<const int, std::ratio<1, 1000>>(123));
+ test(duration<const int, std::ratio<1000, 1>>(123));
+ test(duration<const volatile double>(123.456));
+ test(duration<const arithmetic_wrapper<int>>(arithmetic_wrapper<int>(123)));
+}
+
+int main()
+{
+ test01();
+ test02();
+ test03();
+}
--
2.34.1
smime.p7s
Description: S/MIME Cryptographic Signature
