There are specializations of the atomic
class template for the floating-point types
float,
double, and
long double.

For each such type floating-point,
the specialization atomic<floating-point>
provides additional atomic operations appropriate to floating-point types.

namespace std { template<> struct atomic<floating-point> { using value_type = floating-point; using difference_type = value_type; static constexpr bool is_always_lock_free = implementation-defined; bool is_lock_free() const volatile noexcept; bool is_lock_free() const noexcept; void store(floating-point, memory_order = memory_order_seq_cst) volatile noexcept; void store(floating-point, memory_order = memory_order_seq_cst) noexcept; floating-point load(memory_order = memory_order_seq_cst) volatile noexcept; floating-point load(memory_order = memory_order_seq_cst) noexcept; operator floating-point() volatile noexcept; operator floating-point() noexcept; floating-point exchange(floating-point, memory_order = memory_order_seq_cst) volatile noexcept; floating-point exchange(floating-point, memory_order = memory_order_seq_cst) noexcept; bool compare_exchange_weak(floating-point&, floating-point, memory_order, memory_order) volatile noexcept; bool compare_exchange_weak(floating-point&, floating-point, memory_order, memory_order) noexcept; bool compare_exchange_strong(floating-point&, floating-point, memory_order, memory_order) volatile noexcept; bool compare_exchange_strong(floating-point&, floating-point, memory_order, memory_order) noexcept; bool compare_exchange_weak(floating-point&, floating-point, memory_order = memory_order_seq_cst) volatile noexcept; bool compare_exchange_weak(floating-point&, floating-point, memory_order = memory_order_seq_cst) noexcept; bool compare_exchange_strong(floating-point&, floating-point, memory_order = memory_order_seq_cst) volatile noexcept; bool compare_exchange_strong(floating-point&, floating-point, memory_order = memory_order_seq_cst) noexcept; floating-point fetch_add(floating-point, memory_order = memory_order_seq_cst) volatile noexcept; floating-point fetch_add(floating-point, memory_order = memory_order_seq_cst) noexcept; floating-point fetch_sub(floating-point, memory_order = memory_order_seq_cst) volatile noexcept; floating-point fetch_sub(floating-point, memory_order = memory_order_seq_cst) noexcept; atomic() noexcept = default; constexpr atomic(floating-point) noexcept; atomic(const atomic&) = delete; atomic& operator=(const atomic&) = delete; atomic& operator=(const atomic&) volatile = delete; floating-point operator=(floating-point) volatile noexcept; floating-point operator=(floating-point) noexcept; floating-point operator+=(floating-point) volatile noexcept; floating-point operator+=(floating-point) noexcept; floating-point operator-=(floating-point) volatile noexcept; floating-point operator-=(floating-point) noexcept; }; }

The atomic floating-point specializations
are standard-layout structs.

They each have a trivial default constructor
and a trivial destructor.

The following operations perform arithmetic addition and subtraction computations.

The key, operator, and computation correspondence are identified in
[tab:atomic.arithmetic.computations]Table *tab:atomic.arithmetic.computations.

```
T A::fetch_key(T operand, memory_order order = memory_order_seq_cst) volatile noexcept;
T A::fetch_key(T operand, memory_order order = memory_order_seq_cst) noexcept;
```

Effects:
Atomically replaces the value pointed to by this
with the result of the computation applied to the value pointed
to by this and the given operand.

Memory is affected according to the value of order.

These operations are atomic read-modify-write operations ([intro.multithread]).

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
should conform to the std::numeric_limits<floating-point>
traits associated with the floating-point type ([limits.syn]).

```
T operator op=(T operand) volatile noexcept;
T operator op=(T operand) noexcept;
```

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
should conform to the std::numeric_limits<floating-point>
traits associated with the floating-point type ([limits.syn]).