P1890 C++ Numerics Work In Progress Issues

[wg21bot]

P1890R0 C++ Numerics Work In Progress Issues (Antony Polukhin, Alexander Zaitsev)

[brycelelbach]

Belfast 2019-11 LEWGI Minutes

P1890R0 C++ Numerics Library Issues: Design Review

Chair: Bryce Adelstein Lelbach

Champion: Antony Polukhin

Minute Taker: Conor Hoekstra

Start Review: 11-08 13:41

POLL: An API that is source compatible with C should be a design priority for the overflow detecting functions (C currently does not have these functions and there is no proposal to add them yet).

Strongly For	Weakly For	Neutral	Weakly Against	Strongly Against
1	1	3	3	4

Attendance: 17

# of Authors: 2

Author Position: SF SA

That has consensus against.

// Option 0
constexpr T overflow_add(bool& overflow_occurred, T augend, T addend) noexcept;

// Option 1
constexpr bool overflow_add(T& summand, T augend, T addend) noexcept;

// Option 2 (consistent with the existing builtins modulo argument order)
constexpr bool overflow_add(T* summand, T augend, T addend) noexcept;

// Option 3
template <typename T>
struct overflow_result {
  bool overflow;
  T value;
  // Convertiblity to bool to be explored.
};
constexpr overflow_result<T> overflow_add(T augend, T addend) noexcept;

POLL: API design for the overflow detecting (vote once for your favorite option).

Option	Vote
0	0
1	0
2	2
3	4

Attendance: 17

# of Authors: 2

Author Position: 2 3

Lack of quorum; no consensus.

POLL: The overflow detecting functions should support only fundamental integer types.

Strongly For	Weakly For	Neutral	Weakly Against	Strongly Against
1	2	3	1	2

Attendance: 17

# of Authors: 1

Author Position: A

Lack of quorum; no consensus.

End: 15:27

CONSENSUS: Bring a revision of P1890R0 (C++ Numerics Library Issues), with the guidance below, to LEWGI for further design review.

• Explore modern C++ style APIs for the low-level interfaces such as the overflow detecting functions.
• Make the macros double_word_ops typedefs.
• Explore removing common_type specializations in place of making the types work with the ternary operator.

[brycelelbach]

Closing due to more than 1 year of inactivity. Please re-open if further work is expected.