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libstdc++: Add [[nodiscard]] to chrono conversion functions

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Also add doxygen comments.

libstdc++-v3/ChangeLog:

	* include/bits/chrono.h (duration_cast, floor, round, abs, ceil)
	(time_point_cast): Add [[nodiscard]] attribute and doxygen
	comments.
	(treat_as_floating_point): Add doxygen commen.
This commit is contained in:
Jonathan Wakely 2022-11-28 11:22:24 +00:00
parent 7eec3114eb
commit 646e979c43
1 changed files with 123 additions and 16 deletions
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139
libstdc++-v3/include/bits/chrono.h
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@ -246,8 +246,18 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
/// @endcond
/// duration_cast
/** Convert a `duration` to type `ToDur`.
*
* If the duration cannot be represented accurately in the result type,
* returns the result of integer truncation (i.e., rounded towards zero).
*
* @tparam _ToDur The result type must be a `duration`.
* @param __d A duration.
* @return The value of `__d` converted to type `_ToDur`.
* @since C++11
*/
template<typename _ToDur, typename _Rep, typename _Period>
_GLIBCXX_NODISCARD
constexpr __enable_if_is_duration<_ToDur>
duration_cast(const duration<_Rep, _Period>& __d)
{
@ -260,7 +270,17 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
return __dc::__cast(__d);
}
/// treat_as_floating_point
/** Trait indicating whether to treat a type as a floating-point type.
*
* The chrono library uses this trait to tell whether a `duration` can
* represent fractional values of the given precision, or only integral
* values.
*
* You should specialize this trait for your own numeric types that are
* used with `duration` and can represent non-integral values.
*
* @since C++11
*/
template<typename _Rep>
struct treat_as_floating_point
: is_floating_point<_Rep>
@ -320,8 +340,18 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
#if __cplusplus >= 201703L
# define __cpp_lib_chrono 201611L
/** Convert a `duration` to type `ToDur` and round down.
*
* If the duration cannot be represented exactly in the result type,
* returns the closest value that is less than the argument.
*
* @tparam _ToDur The result type must be a `duration`.
* @param __d A duration.
* @return The value of `__d` converted to type `_ToDur`.
* @since C++17
*/
template<typename _ToDur, typename _Rep, typename _Period>
constexpr __enable_if_is_duration<_ToDur>
[[nodiscard]] constexpr __enable_if_is_duration<_ToDur>
floor(const duration<_Rep, _Period>& __d)
{
auto __to = chrono::duration_cast<_ToDur>(__d);
@ -330,8 +360,18 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
return __to;
}
/** Convert a `duration` to type `ToDur` and round up.
*
* If the duration cannot be represented exactly in the result type,
* returns the closest value that is greater than the argument.
*
* @tparam _ToDur The result type must be a `duration`.
* @param __d A duration.
* @return The value of `__d` converted to type `_ToDur`.
* @since C++17
*/
template<typename _ToDur, typename _Rep, typename _Period>
constexpr __enable_if_is_duration<_ToDur>
[[nodiscard]] constexpr __enable_if_is_duration<_ToDur>
ceil(const duration<_Rep, _Period>& __d)
{
auto __to = chrono::duration_cast<_ToDur>(__d);
@ -340,8 +380,20 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
return __to;
}
/** Convert a `duration` to type `ToDur` and round to the closest value.
*
* If the duration cannot be represented exactly in the result type,
* returns the closest value, rounding ties to even.
*
* @tparam _ToDur The result type must be a `duration` with a
* non-floating-point `rep` type.
* @param __d A duration.
* @return The value of `__d` converted to type `_ToDur`.
* @since C++17
*/
template <typename _ToDur, typename _Rep, typename _Period>
constexpr enable_if_t<
[[nodiscard]] constexpr
enable_if_t<
__and_<__is_duration<_ToDur>,
__not_<treat_as_floating_point<typename _ToDur::rep>>>::value,
_ToDur>
@ -352,18 +404,24 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
auto __diff0 = __d - __t0;
auto __diff1 = __t1 - __d;
if (__diff0 == __diff1)
{
{
if (__t0.count() & 1)
return __t1;
return __t1;
return __t0;
}
}
else if (__diff0 < __diff1)
return __t0;
return __t0;
return __t1;
}
/** The absolute (non-negative) value of a duration.
*
* @param __d A duration with a signed `rep` type.
* @return A duration of the same type as the argument, with value |d|.
* @since C++17
*/
template<typename _Rep, typename _Period>
constexpr
[[nodiscard]] constexpr
enable_if_t<numeric_limits<_Rep>::is_signed, duration<_Rep, _Period>>
abs(duration<_Rep, _Period> __d)
{
@ -925,10 +983,21 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
duration __d;
};
/// time_point_cast
/** Convert a `time_point` to use `duration` type `ToDur`.
*
* The result is the same time point as measured by the same clock, but
* using the specified `duration` to represent the time.
* If the time point cannot be represented accurately in the result type,
* returns the result of integer truncation (i.e., rounded towards zero).
*
* @tparam _ToDur The `duration` type to use for the result.
* @param __t A time point.
* @return The value of `__t` converted to use type `_ToDur`.
* @since C++11
*/
template<typename _ToDur, typename _Clock, typename _Dur>
constexpr typename enable_if<__is_duration<_ToDur>::value,
time_point<_Clock, _ToDur>>::type
_GLIBCXX_NODISCARD constexpr
__enable_if_t<__is_duration<_ToDur>::value, time_point<_Clock, _ToDur>>
time_point_cast(const time_point<_Clock, _Dur>& __t)
{
typedef time_point<_Clock, _ToDur> __time_point;
@ -936,8 +1005,20 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
}
#if __cplusplus > 201402L
/** Convert a `time_point` to type `ToDur` and round down.
*
* The result is the same time point as measured by the same clock, but
* using the specified `duration` to represent the time.
* If the time point cannot be represented exactly in the result type,
* returns the closest value that is less than the argument.
*
* @tparam _ToDur The `duration` type to use for the result.
* @param __t A time point.
* @return The value of `__d` converted to type `_ToDur`.
* @since C++17
*/
template<typename _ToDur, typename _Clock, typename _Dur>
constexpr
[[nodiscard]] constexpr
enable_if_t<__is_duration<_ToDur>::value, time_point<_Clock, _ToDur>>
floor(const time_point<_Clock, _Dur>& __tp)
{
@ -945,8 +1026,20 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
chrono::floor<_ToDur>(__tp.time_since_epoch())};
}
/** Convert a `time_point` to type `ToDur` and round up.
*
* The result is the same time point as measured by the same clock, but
* using the specified `duration` to represent the time.
* If the time point cannot be represented exactly in the result type,
* returns the closest value that is greater than the argument.
*
* @tparam _ToDur The `duration` type to use for the result.
* @param __t A time point.
* @return The value of `__d` converted to type `_ToDur`.
* @since C++17
*/
template<typename _ToDur, typename _Clock, typename _Dur>
constexpr
[[nodiscard]] constexpr
enable_if_t<__is_duration<_ToDur>::value, time_point<_Clock, _ToDur>>
ceil(const time_point<_Clock, _Dur>& __tp)
{
@ -954,8 +1047,22 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
chrono::ceil<_ToDur>(__tp.time_since_epoch())};
}
/** Convert a `time_point` to type `ToDur` and round to the closest value.
*
* The result is the same time point as measured by the same clock, but
* using the specified `duration` to represent the time.
* If the time point cannot be represented exactly in the result type,
* returns the closest value, rounding ties to even.
*
* @tparam _ToDur The `duration` type to use for the result,
* which must have a non-floating-point `rep` type.
* @param __t A time point.
* @return The value of `__d` converted to type `_ToDur`.
* @since C++17
*/
template<typename _ToDur, typename _Clock, typename _Dur>
constexpr enable_if_t<
[[nodiscard]] constexpr
enable_if_t<
__and_<__is_duration<_ToDur>,
__not_<treat_as_floating_point<typename _ToDur::rep>>>::value,
time_point<_Clock, _ToDur>>