32 Concurrency support library [thread]

32.5 Atomic operations [atomics]

32.5.7 Class template atomic_ref [atomics.ref.generic]

32.5.7.4 Specializations for floating-point types [atomics.ref.float]

There are specializations of the atomic_ref class template for all floating-point types.
For each such type floating-point-type, the specialization atomic_ref<floating-point> provides additional atomic operations appropriate to floating-point types.
The program is ill-formed if is_always_lock_free is false and is_volatile_v<T> is true.
namespace std { template<> struct atomic_ref<floating-point-type> { private: floating-point-type* ptr; // exposition only public: using value_type = remove_cv_t<floating-point-type>; using difference_type = value_type; static constexpr size_t required_alignment = implementation-defined; static constexpr bool is_always_lock_free = implementation-defined; bool is_lock_free() const noexcept; constexpr explicit atomic_ref(floating-point-type&); constexpr atomic_ref(const atomic_ref&) noexcept; atomic_ref& operator=(const atomic_ref&) = delete; constexpr void store(floating-point-type, memory_order = memory_order::seq_cst) const noexcept; constexpr value_type operator=(value_type) const noexcept; constexpr value_type load(memory_order = memory_order::seq_cst) const noexcept; constexpr operator floating-point-type() const noexcept; constexpr value_type exchange(floating-point-type, memory_order = memory_order::seq_cst) const noexcept; constexpr bool compare_exchange_weak(value_type&, floating-point-type, memory_order, memory_order) const noexcept; constexpr bool compare_exchange_strong(value_type&, floating-point-type, memory_order, memory_order) const noexcept; constexpr bool compare_exchange_weak(value_type&, floating-point-type, memory_order = memory_order::seq_cst) const noexcept; constexpr bool compare_exchange_strong(value_type&, floating-point-type, memory_order = memory_order::seq_cst) const noexcept; constexpr value_type fetch_add(floating-point-type, memory_order = memory_order::seq_cst) const noexcept; constexpr value_type fetch_sub(floating-point-type, memory_order = memory_order::seq_cst) const noexcept; constexpr value_type operator+=(value_type) const noexcept; constexpr value_type operator-=(value_type) const noexcept; constexpr void wait(floating-point-type, memory_order = memory_order::seq_cst) const noexcept; constexpr void notify_one() const noexcept; constexpr void notify_all() const noexcept; constexpr floating-point-type* address() const noexcept; }; }
Descriptions are provided below only for members that differ from the primary template.
The following operations perform arithmetic computations.
The correspondence among key, operator, and computation is specified in Table 150.
constexpr value_type fetch_key(value_type operand, memory_order order = memory_order::seq_cst) const noexcept;
Constraints: is_const_v<floating-point-type> is false.
Effects: Atomically replaces the value referenced by *ptr with the result of the computation applied to the value referenced by *ptr and the given operand.
Memory is affected according to the value of order.
These operations are atomic read-modify-write operations ([intro.races]).
Returns: Atomically, the value referenced by *ptr immediately before the effects.
Remarks: If the result is not a representable value for its type ([expr.pre]), the result is unspecified, but the operations otherwise have no undefined behavior.
Atomic arithmetic operations on floating-point-type should conform to the std​::​numeric_limits<value_type> traits associated with the floating-point type ([limits.syn]).
The floating-point environment ([cfenv]) for atomic arithmetic operations on floating-
point-type
may be different than the calling thread's floating-point environment.
constexpr value_type operator op=(value_type operand) const noexcept;
Constraints: is_const_v<floating-point-type> is false.
Effects: Equivalent to: return fetch_key(operand) op operand;