<numeric>: check for gcd / lcm overflows by AlexGuteniev · Pull Request #4776 · microsoft/STL (original) (raw)

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In compile time or in debug.

Fixes #2300

In compile time or in debug. Applies to C++20 and later mode.

_Mul_overflow is made to only handle non-bool integer types in C++17.

Backport overflow checking of lcm/gcd to C++17

I'm mirroring this to the MSVC-internal repo - please notify me if any further changes are pushed.

numeric: Add a static_cast when dividing _Common_unsigned by _Common_unsigned, due to the usual arithmetic conversions which will emit sign conversion warnings for tiny types.

utility:

• Move _Is_standard_integer down to the _HAS_CXX20 region. (It's also used by <mdspan>.)
• Relax the internal _Cmp_equal, _Cmp_less, and _In_range to accept nonbool integrals.
  • Because they're internal, we can _STL_INTERNAL_STATIC_ASSERT.
  • Comment that this "allows character types".
• Enforce _Is_standard_integer at the user-visible layer.

P0295R0_gcd_lcm: Add test coverage, because gcd/lcm are required to accept nonbool integrals. (An MSVC-internal test found this by using char.)

I pushed a commit:

Fix gcd/lcm to work with all nonbool integrals.

numeric: Add a static_cast when dividing _Common_unsigned by _Common_unsigned, due to the usual arithmetic conversions which will emit sign conversion warnings for tiny types.

utility:

• Move _Is_standard_integer down to the _HAS_CXX20 region. (It's also used by <mdspan>.)
• Relax the internal _Cmp_equal, _Cmp_less, and _In_range to accept nonbool integrals.
  • Because they're internal, we can _STL_INTERNAL_STATIC_ASSERT.
  • Comment that this "allows character types".
• Enforce _Is_standard_integer at the user-visible layer.

P0295R0_gcd_lcm: Add test coverage, because gcd/lcm are required to accept nonbool integrals. (An MSVC-internal test found this by using char.)

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Could be useful to comment that this can be used to test for standard and extended integer types, because there are no extended integer types (probably in a subsequent change)

Thanks for implementing these checks! My internal branch was dev/stl/least-common-meowtiple 😹 🧮 📈