33 Concurrency support library [thread]

33.5 Atomic operations [atomics]

33.5.7 Class template atomic_ref [atomics.ref.generic]

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

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There are specializations of the atomic_ref class template for all cv-unqualified 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.
namespace std { template<> struct atomic_ref<floating-point-type> { private: floating-point-type* ptr; // exposition only public: using value_type = 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; explicit atomic_ref(floating-point-type&); atomic_ref(const atomic_ref&) noexcept; atomic_ref& operator=(const atomic_ref&) = delete; void store(floating-point-type, memory_order = memory_order::seq_cst) const noexcept; floating-point-type operator=(floating-point-type) const noexcept; floating-point-type load(memory_order = memory_order::seq_cst) const noexcept; operator floating-point-type() const noexcept; floating-point-type exchange(floating-point-type, memory_order = memory_order::seq_cst) const noexcept; bool compare_exchange_weak(floating-point-type&, floating-point-type, memory_order, memory_order) const noexcept; bool compare_exchange_strong(floating-point-type&, floating-point-type, memory_order, memory_order) const noexcept; bool compare_exchange_weak(floating-point-type&, floating-point-type, memory_order = memory_order::seq_cst) const noexcept; bool compare_exchange_strong(floating-point-type&, floating-point-type, memory_order = memory_order::seq_cst) const noexcept; floating-point-type fetch_add(floating-point-type, memory_order = memory_order::seq_cst) const noexcept; floating-point-type fetch_sub(floating-point-type, memory_order = memory_order::seq_cst) const noexcept; floating-point-type operator+=(floating-point-type) const noexcept; floating-point-type operator-=(floating-point-type) const noexcept; void wait(floating-point-type, memory_order = memory_order::seq_cst) const noexcept; void notify_one() const noexcept; void notify_all() const noexcept; }; }
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Descriptions are provided below only for members that differ from the primary template.
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The following operations perform arithmetic computations.
The correspondence among key, operator, and computation is specified in Table 145.
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floating-point-type fetch_key(floating-point-type operand, memory_order order = memory_order::seq_cst) const noexcept;
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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]).
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Returns: Atomically, the value referenced by *ptr immediately before the effects.
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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<floating-point-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.
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floating-point-type operator op=(floating-point-type operand) const noexcept;
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Effects: Equivalent to: return fetch_key(operand) op operand;