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cppdraft/time/traits/duration/values.md

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+[time.traits.duration.values]
+
+# 30 Time library [[time]](./#time)
+
+## 30.4 Time-related traits [[time.traits]](time.traits#duration.values)
+
+### 30.4.2 duration_values [time.traits.duration.values]
+
+[🔗](#lib:duration_values)
+
+`template<class Rep>
+  struct duration_values {
+  public:
+    static constexpr Rep zero() noexcept;
+    static constexpr Rep min() noexcept;
+    static constexpr Rep max() noexcept;
+  };
+`
+
+[1](#1)
+
+[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/time.tex#L1098)
+
+The duration template uses the duration_values trait to
+construct special values of the duration's representation (Rep)[.](#1.sentence-1)
+
+This is
+done because the representation can be a class type with behavior that
+requires some other implementation to return these special values[.](#1.sentence-2)
+
+In that case,
+the author of that class type should specialize duration_values to
+return the indicated values[.](#1.sentence-3)
+
+[🔗](#lib:zero,duration_values)
+
+`static constexpr Rep zero() noexcept;
+`
+
+[2](#2)
+
+[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/time.tex#L1112)
+
+*Returns*: Rep(0)[.](#2.sentence-1)
+
+[*Note [1](#note-1)*:
+
+Rep(0) is specified instead ofRep() because Rep() can have some other meaning, such as an
+uninitialized value[.](#2.sentence-2)
+
+— *end note*]
+
+[3](#3)
+
+[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/time.tex#L1121)
+
+*Remarks*: The value returned shall be the additive identity[.](#3.sentence-1)
+
+[🔗](#lib:min,duration_values)
+
+`static constexpr Rep min() noexcept;
+`
+
+[4](#4)
+
+[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/time.tex#L1132)
+
+*Returns*: numeric_limits<Rep>​::​lowest()[.](#4.sentence-1)
+
+[5](#5)
+
+[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/time.tex#L1136)
+
+*Remarks*: The value returned shall compare less than or equal to zero()[.](#5.sentence-1)
+
+[🔗](#lib:max,duration_values)
+
+`static constexpr Rep max() noexcept;
+`
+
+[6](#6)
+
+[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/time.tex#L1147)
+
+*Returns*: numeric_limits<Rep>​::​max()[.](#6.sentence-1)
+
+[7](#7)
+
+[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/time.tex#L1151)
+
+*Remarks*: The value returned shall compare greater than zero()[.](#7.sentence-1)

cppdraft/time/traits/is/clock.md

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+[time.traits.is.clock]
+
+# 30 Time library [[time]](./#time)
+
+## 30.4 Time-related traits [[time.traits]](time.traits#is.clock)
+
+### 30.4.4 Class template is_clock [time.traits.is.clock]
+
+[🔗](#lib:is_clock)
+
+`template<class T> struct is_clock;
+`
+
+[1](#1)
+
+[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/time.tex#L1205)
+
+is_clock is a [*Cpp17UnaryTypeTrait*](meta.rqmts#:Cpp17UnaryTypeTrait "21.3.2 Requirements [meta.rqmts]") ([[meta.rqmts]](meta.rqmts "21.3.2 Requirements"))
+with a base characteristic of true_type if T meets the [*Cpp17Clock*](time.clock.req#:Cpp17Clock "30.3 Cpp17Clock requirements [time.clock.req]") requirements ([[time.clock.req]](time.clock.req "30.3 Cpp17Clock requirements")),
+otherwise false_type[.](#1.sentence-1)
+
+For the purposes of the specification of this trait,
+the extent to which an implementation determines
+that a type cannot meet the [*Cpp17Clock*](time.clock.req#:Cpp17Clock "30.3 Cpp17Clock requirements [time.clock.req]") requirements is unspecified,
+except that as a minimum
+a type T shall not qualify as a [*Cpp17Clock*](time.clock.req#:Cpp17Clock "30.3 Cpp17Clock requirements [time.clock.req]") unless it meets all of the following conditions:
+
+- [(1.1)](#1.1)
+
+the [*qualified-id*](expr.prim.id.qual#nt:qualified-id "7.5.5.3 Qualified names [expr.prim.id.qual]")*s*T​::​rep,T​::​period,T​::​duration, andT​::​time_point are valid and each denotes a type ([[temp.deduct]](temp.deduct "13.10.3 Template argument deduction")),
+
+- [(1.2)](#1.2)
+
+the expressionT​::​is_steady is well-formed when treated as an [unevaluated operand](expr.context#def:unevaluated_operand "7.2.3 Context dependence [expr.context]"),
+
+- [(1.3)](#1.3)
+
+the expressionT​::​now() is well-formed when treated as an unevaluated operand[.](#1.sentence-2)
+
+[2](#2)
+
+[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/time.tex#L1231)
+
+The behavior of a program that adds specializations for is_clock is undefined[.](#2.sentence-1)

cppdraft/time/traits/is/fp.md

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+[time.traits.is.fp]
+
+# 30 Time library [[time]](./#time)
+
+## 30.4 Time-related traits [[time.traits]](time.traits#is.fp)
+
+### 30.4.1 treat_as_floating_point [time.traits.is.fp]
+
+[🔗](#lib:treat_as_floating_point)
+
+`template<class Rep> struct treat_as_floating_point : is_floating_point<Rep> { };
+`
+
+[1](#1)
+
+[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/time.tex#L1071)
+
+The duration template uses the treat_as_floating_point trait to
+help determine if a duration object can be converted to anotherduration with a different tick period[.](#1.sentence-1)
+
+Iftreat_as_floating_point_v<Rep> is true, then implicit conversions
+are allowed among durations[.](#1.sentence-2)
+
+Otherwise, the implicit convertibility
+depends on the tick periods of the durations[.](#1.sentence-3)
+
+[*Note [1](#note-1)*:
+
+The intention of this trait is to indicate whether a given class behaves like a floating-point
+type, and thus allows division of one value by another with acceptable loss of precision[.](#1.sentence-4)
+
+Iftreat_as_floating_point_v<Rep> is false, Rep will be treated as
+if it behaved like an integral type for the purpose of these conversions[.](#1.sentence-5)
+
+— *end note*]

cppdraft/time/traits/specializations.md

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+[time.traits.specializations]
+
+# 30 Time library [[time]](./#time)
+
+## 30.4 Time-related traits [[time.traits]](time.traits#specializations)
+
+### 30.4.3 Specializations of common_type [time.traits.specializations]
+
+[🔗](#lib:common_type)
+
+`template<class Rep1, class Period1, class Rep2, class Period2>
+  struct common_type<chrono::duration<Rep1, Period1>, chrono::duration<Rep2, Period2>> {
+    using type = chrono::duration<common_type_t<Rep1, Rep2>, see below>;
+  };
+`
+
+[1](#1)
+
+[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/time.tex#L1166)
+
+The period of the duration indicated by this specialization ofcommon_type is the greatest common divisor of Period1 andPeriod2[.](#1.sentence-1)
+
+[*Note [1](#note-1)*:
+
+This can be computed by forming a ratio of the
+greatest common divisor of Period1​::​num and Period2​::​num and the
+least common multiple of Period1​::​den and Period2​::​den[.](#1.sentence-2)
+
+— *end note*]
+
+[2](#2)
+
+[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/time.tex#L1176)
+
+[*Note [2](#note-2)*:
+
+The typedef name type is a synonym for theduration with the largest tick period possible where bothduration arguments will convert to it without requiring a division
+operation[.](#2.sentence-1)
+
+The representation of this type is intended to be able to hold any
+value resulting from this conversion with no truncation error, although
+floating-point durations can have round-off errors[.](#2.sentence-2)
+
+— *end note*]
+
+[🔗](#lib:common_type,duration)
+
+`template<class Clock, class Duration1, class Duration2>
+  struct common_type<chrono::time_point<Clock, Duration1>, chrono::time_point<Clock, Duration2>> {
+    using type = chrono::time_point<Clock, common_type_t<Duration1, Duration2>>;
+  };
+`
+
+[3](#3)
+
+[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/time.tex#L1194)
+
+The common type of two time_point types is a time_point with the same
+clock as the two types and the common type of their two durations[.](#3.sentence-1)