tmp/tmpue02dke5/{from.md → to.md}
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| 1 |
+
### Specializations for floating-point types <a id="atomics.types.float">[[atomics.types.float]]</a>
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| 2 |
+
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| 3 |
+
There are specializations of the `atomic` class template for the
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| 4 |
+
floating-point types `float`, `double`, and `long double`. For each such
|
| 5 |
+
type `floating-point`, the specialization `atomic<floating-point>`
|
| 6 |
+
provides additional atomic operations appropriate to floating-point
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| 7 |
+
types.
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| 8 |
+
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| 9 |
+
``` cpp
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| 10 |
+
namespace std {
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| 11 |
+
template<> struct atomic<floating-point> {
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| 12 |
+
using value_type = floating-point;
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| 13 |
+
using difference_type = value_type;
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| 14 |
+
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| 15 |
+
static constexpr bool is_always_lock_free = implementation-defined // whether a given atomic type's operations are always lock free;
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| 16 |
+
bool is_lock_free() const volatile noexcept;
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| 17 |
+
bool is_lock_free() const noexcept;
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| 18 |
+
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| 19 |
+
constexpr atomic() noexcept;
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| 20 |
+
constexpr atomic(floating-point) noexcept;
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| 21 |
+
atomic(const atomic&) = delete;
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| 22 |
+
atomic& operator=(const atomic&) = delete;
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| 23 |
+
atomic& operator=(const atomic&) volatile = delete;
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| 24 |
+
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| 25 |
+
void store(floating-point, memory_order = memory_order::seq_cst) volatile noexcept;
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| 26 |
+
void store(floating-point, memory_order = memory_order::seq_cst) noexcept;
|
| 27 |
+
floating-point operator=(floating-point) volatile noexcept;
|
| 28 |
+
floating-point operator=(floating-point) noexcept;
|
| 29 |
+
floating-point load(memory_order = memory_order::seq_cst) volatile noexcept;
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| 30 |
+
floating-point load(memory_order = memory_order::seq_cst) noexcept;
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| 31 |
+
operator floating-point() volatile noexcept;
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| 32 |
+
operator floating-point() noexcept;
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| 33 |
+
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| 34 |
+
floating-point exchange(floating-point,
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| 35 |
+
memory_order = memory_order::seq_cst) volatile noexcept;
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| 36 |
+
floating-point exchange(floating-point,
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| 37 |
+
memory_order = memory_order::seq_cst) noexcept;
|
| 38 |
+
bool compare_exchange_weak(floating-point&, floating-point,
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| 39 |
+
memory_order, memory_order) volatile noexcept;
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| 40 |
+
bool compare_exchange_weak(floating-point&, floating-point,
|
| 41 |
+
memory_order, memory_order) noexcept;
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| 42 |
+
bool compare_exchange_strong(floating-point&, floating-point,
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| 43 |
+
memory_order, memory_order) volatile noexcept;
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| 44 |
+
bool compare_exchange_strong(floating-point&, floating-point,
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| 45 |
+
memory_order, memory_order) noexcept;
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| 46 |
+
bool compare_exchange_weak(floating-point&, floating-point,
|
| 47 |
+
memory_order = memory_order::seq_cst) volatile noexcept;
|
| 48 |
+
bool compare_exchange_weak(floating-point&, floating-point,
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| 49 |
+
memory_order = memory_order::seq_cst) noexcept;
|
| 50 |
+
bool compare_exchange_strong(floating-point&, floating-point,
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| 51 |
+
memory_order = memory_order::seq_cst) volatile noexcept;
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| 52 |
+
bool compare_exchange_strong(floating-point&, floating-point,
|
| 53 |
+
memory_order = memory_order::seq_cst) noexcept;
|
| 54 |
+
|
| 55 |
+
floating-point fetch_add(floating-point,
|
| 56 |
+
memory_order = memory_order::seq_cst) volatile noexcept;
|
| 57 |
+
floating-point fetch_add(floating-point,
|
| 58 |
+
memory_order = memory_order::seq_cst) noexcept;
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| 59 |
+
floating-point fetch_sub(floating-point,
|
| 60 |
+
memory_order = memory_order::seq_cst) volatile noexcept;
|
| 61 |
+
floating-point fetch_sub(floating-point,
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| 62 |
+
memory_order = memory_order::seq_cst) noexcept;
|
| 63 |
+
|
| 64 |
+
floating-point operator+=(floating-point) volatile noexcept;
|
| 65 |
+
floating-point operator+=(floating-point) noexcept;
|
| 66 |
+
floating-point operator-=(floating-point) volatile noexcept;
|
| 67 |
+
floating-point operator-=(floating-point) noexcept;
|
| 68 |
+
|
| 69 |
+
void wait(floating-point, memory_order = memory_order::seq_cst) const volatile noexcept;
|
| 70 |
+
void wait(floating-point, memory_order = memory_order::seq_cst) const noexcept;
|
| 71 |
+
void notify_one() volatile noexcept;
|
| 72 |
+
void notify_one() noexcept;
|
| 73 |
+
void notify_all() volatile noexcept;
|
| 74 |
+
void notify_all() noexcept;
|
| 75 |
+
};
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| 76 |
+
}
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| 77 |
+
```
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| 78 |
+
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| 79 |
+
The atomic floating-point specializations are standard-layout structs.
|
| 80 |
+
They each have a trivial destructor.
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| 81 |
+
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| 82 |
+
Descriptions are provided below only for members that differ from the
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| 83 |
+
primary template.
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| 84 |
+
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| 85 |
+
The following operations perform arithmetic addition and subtraction
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| 86 |
+
computations. The key, operator, and computation correspondence are
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| 87 |
+
identified in [[atomic.types.int.comp]].
|
| 88 |
+
|
| 89 |
+
``` cpp
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| 90 |
+
T fetch_key(T operand, memory_order order = memory_order::seq_cst) volatile noexcept;
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| 91 |
+
T fetch_key(T operand, memory_order order = memory_order::seq_cst) noexcept;
|
| 92 |
+
```
|
| 93 |
+
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| 94 |
+
*Constraints:* For the `volatile` overload of this function,
|
| 95 |
+
`is_always_lock_free` is `true`.
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| 96 |
+
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| 97 |
+
*Effects:* Atomically replaces the value pointed to by `this` with the
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| 98 |
+
result of the computation applied to the value pointed to by `this` and
|
| 99 |
+
the given `operand`. Memory is affected according to the value of
|
| 100 |
+
`order`. These operations are atomic read-modify-write
|
| 101 |
+
operations [[intro.multithread]].
|
| 102 |
+
|
| 103 |
+
*Returns:* Atomically, the value pointed to by `this` immediately before
|
| 104 |
+
the effects.
|
| 105 |
+
|
| 106 |
+
*Remarks:* If the result is not a representable value for its
|
| 107 |
+
type [[expr.pre]] the result is unspecified, but the operations
|
| 108 |
+
otherwise have no undefined behavior. Atomic arithmetic operations on
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| 109 |
+
*`floating-point`* should conform to the
|
| 110 |
+
`std::numeric_limits<`*`floating-point`*`>` traits associated with the
|
| 111 |
+
floating-point type [[limits.syn]]. The floating-point
|
| 112 |
+
environment [[cfenv]] for atomic arithmetic operations on
|
| 113 |
+
*`floating-point`* may be different than the calling thread’s
|
| 114 |
+
floating-point environment.
|
| 115 |
+
|
| 116 |
+
``` cpp
|
| 117 |
+
T operator op=(T operand) volatile noexcept;
|
| 118 |
+
T operator op=(T operand) noexcept;
|
| 119 |
+
```
|
| 120 |
+
|
| 121 |
+
*Constraints:* For the `volatile` overload of this function,
|
| 122 |
+
`is_always_lock_free` is `true`.
|
| 123 |
+
|
| 124 |
+
*Effects:* Equivalent to:
|
| 125 |
+
`return fetch_`*`key`*`(operand) `*`op`*` operand;`
|
| 126 |
+
|
| 127 |
+
*Remarks:* If the result is not a representable value for its
|
| 128 |
+
type [[expr.pre]] the result is unspecified, but the operations
|
| 129 |
+
otherwise have no undefined behavior. Atomic arithmetic operations on
|
| 130 |
+
*`floating-point`* should conform to the
|
| 131 |
+
`std::numeric_limits<`*`floating-point`*`>` traits associated with the
|
| 132 |
+
floating-point type [[limits.syn]]. The floating-point
|
| 133 |
+
environment [[cfenv]] for atomic arithmetic operations on
|
| 134 |
+
*`floating-point`* may be different than the calling thread’s
|
| 135 |
+
floating-point environment.
|
| 136 |
+
|