1   Motivation

This paper proposes an extension to the atomic operations library [atomics] for atomic addition on an object conforming to the atomic-view-concept (see P0019, Atomic View) instantiated for a floating point type. A class conforming to the atomic-view-concept shall also provide the following operations when T is a floating-point type. This capability is critical for high performance computing (HPC) applications.

2   Proposal

[Note: In 3.9.1p8 floating point types are also refered to as floating types. - end note]

Add to 29.5, Atomic Types, before 29.5p1.

template<> struct atomic< floating > {

floating fetch_add( floating operand , memory_order order = memory_order_seq_cst ) volatile noexcept;

floating fetch_add( floating operand , memory_order order = memory_order_seq_cst ) noexcept;

floating fetch_sub( floating operand , memory_order order = memory_order_seq_cst ) volatile noexcept;

floating fetch_sub( floating operand , memory_order order = memory_order_seq_cst ) noexcept;

floating operator+=( floating operand ) volatile noexcept;

floating operator+=( floating operand ) noexcept;

floating operator-=( floating operand ) volatile noexcept;

floating operator-=( floating operand ) noexcept;

};

template<> struct atomic-view-concept < floating > {

floating fetch_add( floating operand , memory_order order = memory_order_seq_cst ) const noexcept;

floating fetch_sub( floating operand , memory_order order = memory_order_seq_cst ) const noexcept;

floating operator+=( floating operand ) const noexcept;

floating operator-=( floating operand ) const noexcept;

};

Insert into the listed types in 29.5p5:

floating specializations

Insert new paragraph after 29.6.5p30.

Remark: For floating types atomic arithmatic operations should conform to std::numeric_limits< floating > (18.3.2) traits associated with the floating point type. The floating point environment (26.3) for these operations may be different that the calling thread's floating point environment.