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[libc++][math] Add constexpr for std::abs() #146633

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[libc++][math] Add constexpr for std::abs() #146633

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5c135a1
Update abs test
arjunUpatel Jul 2, 2025
32d133a
Make abs traits constexpr
arjunUpatel Jul 2, 2025
c843467
Update clang cpp23 constexpr tests
arjunUpatel Jul 2, 2025
4f49c87
Update gcc cpp23 constexpr tests
arjunUpatel Jul 2, 2025
c07b0d8
Check constexpr builtins for clang
arjunUpatel Jul 2, 2025
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12 changes: 6 additions & 6 deletions libcxx/include/__math/abs.h
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Expand Up @@ -41,25 +41,25 @@ template <class _A1, __enable_if_t<is_integral<_A1>::value, int> = 0>

// abs

[[__nodiscard__]] _LIBCPP_HIDE_FROM_ABI inline float abs(float __x) _NOEXCEPT { return __builtin_fabsf(__x); }
[[__nodiscard__]] _LIBCPP_HIDE_FROM_ABI inline double abs(double __x) _NOEXCEPT { return __builtin_fabs(__x); }
[[__nodiscard__]] _LIBCPP_CONSTEXPR_SINCE_CXX23 _LIBCPP_HIDE_FROM_ABI inline float abs(float __x) _NOEXCEPT { return __builtin_fabsf(__x); }
[[__nodiscard__]] _LIBCPP_CONSTEXPR_SINCE_CXX23 _LIBCPP_HIDE_FROM_ABI inline double abs(double __x) _NOEXCEPT { return __builtin_fabs(__x); }

[[__nodiscard__]] _LIBCPP_HIDE_FROM_ABI inline long double abs(long double __x) _NOEXCEPT {
[[__nodiscard__]] _LIBCPP_CONSTEXPR_SINCE_CXX23 _LIBCPP_HIDE_FROM_ABI inline long double abs(long double __x) _NOEXCEPT {
return __builtin_fabsl(__x);
}

template <class = int>
[[__nodiscard__]] _LIBCPP_HIDE_FROM_ABI inline int abs(int __x) _NOEXCEPT {
[[__nodiscard__]] _LIBCPP_CONSTEXPR_SINCE_CXX23 _LIBCPP_HIDE_FROM_ABI inline int abs(int __x) _NOEXCEPT {
return __builtin_abs(__x);
}

template <class = int>
[[__nodiscard__]] _LIBCPP_HIDE_FROM_ABI inline long abs(long __x) _NOEXCEPT {
[[__nodiscard__]] _LIBCPP_CONSTEXPR_SINCE_CXX23 _LIBCPP_HIDE_FROM_ABI inline long abs(long __x) _NOEXCEPT {
return __builtin_labs(__x);
}

template <class = int>
[[__nodiscard__]] _LIBCPP_HIDE_FROM_ABI inline long long abs(long long __x) _NOEXCEPT {
[[__nodiscard__]] _LIBCPP_CONSTEXPR_SINCE_CXX23 _LIBCPP_HIDE_FROM_ABI inline long long abs(long long __x) _NOEXCEPT {
return __builtin_llabs(__x);
}

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37 changes: 31 additions & 6 deletions libcxx/test/libcxx/numerics/c.math/constexpr-cxx23-clang.pass.cpp
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Expand Up @@ -40,12 +40,37 @@ int main(int, char**) {
double DummyDouble;
long double DummyLongDouble;

ASSERT_NOT_CONSTEXPR_CXX23(std::abs(-1) == 1);
ASSERT_NOT_CONSTEXPR_CXX23(std::abs(-1L) == 1L);
ASSERT_NOT_CONSTEXPR_CXX23(std::abs(-1LL) == 1LL);
ASSERT_NOT_CONSTEXPR_CXX23(std::abs(-1.0f) == 1.0f);
ASSERT_NOT_CONSTEXPR_CXX23(std::abs(-1.0) == 1.0);
ASSERT_NOT_CONSTEXPR_CXX23(std::abs(-1.0L) == 1.0L);
// TODO(LLVM 22): Remove `__has_constexpr_builtin` conditional once support for Clang 19 is dropped.
#if __has_constexpr_builtin(__builtin_abs)
ASSERT_CONSTEXPR_CXX23(std::abs(-1) == 1);
#else
ASSERT_NOT_CONSTEXPR_CXX23(std::abs(-1) == 1);
#endif
#if __has_constexpr_builtin(__builtin_labs)
ASSERT_CONSTEXPR_CXX23(std::abs(-1L) == 1L);
#else
ASSERT_NOT_CONSTEXPR_CXX23(std::abs(-1L) == 1L);
#endif
#if __has_constexpr_builtin(__builtin_llabs)
ASSERT_CONSTEXPR_CXX23(std::abs(-1LL) == 1LL);
#else
ASSERT_NOT_CONSTEXPR_CXX23(std::abs(-1LL) == 1LL);
#endif
#if __has_constexpr_builtin(__builtin_fabsf)
ASSERT_CONSTEXPR_CXX23(std::abs(-1.0f) == 1.0f);
#else
ASSERT_NOT_CONSTEXPR_CXX23(std::abs(-1.0f) == 1.0f);
#endif
#if __has_constexpr_builtin(__builtin_fabs)
ASSERT_CONSTEXPR_CXX23(std::abs(-1.0) == 1.0);
#else
ASSERT_NOT_CONSTEXPR_CXX23(std::abs(-1.0) == 1.0);
#endif
#if __has_constexpr_builtin(__builtin_fabsl)
ASSERT_CONSTEXPR_CXX23(std::abs(-1.0L) == 1.0L);
#else
ASSERT_NOT_CONSTEXPR_CXX23(std::abs(-1.0L) == 1.0L);
#endif

ASSERT_NOT_CONSTEXPR_CXX23(std::labs(-1L) == 1L);
ASSERT_NOT_CONSTEXPR_CXX23(std::llabs(-1LL) == 1LL);
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10 changes: 5 additions & 5 deletions libcxx/test/libcxx/numerics/c.math/constexpr-cxx23-gcc.pass.cpp
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Expand Up @@ -38,11 +38,11 @@ int main(int, char**) {
long double DummyLongDouble;

ASSERT_CONSTEXPR_CXX23(std::abs(-1) == 1);
ASSERT_NOT_CONSTEXPR_CXX23(std::abs(-1L) == 1L);
ASSERT_NOT_CONSTEXPR_CXX23(std::abs(-1LL) == 1LL);
ASSERT_NOT_CONSTEXPR_CXX23(std::abs(-1.0f) == 1.0f);
ASSERT_NOT_CONSTEXPR_CXX23(std::abs(-1.0) == 1.0);
ASSERT_NOT_CONSTEXPR_CXX23(std::abs(-1.0L) == 1.0L);
ASSERT_CONSTEXPR_CXX23(std::abs(-1L) == 1L);
ASSERT_CONSTEXPR_CXX23(std::abs(-1LL) == 1LL);
ASSERT_CONSTEXPR_CXX23(std::abs(-1.0f) == 1.0f);
ASSERT_CONSTEXPR_CXX23(std::abs(-1.0) == 1.0);
ASSERT_CONSTEXPR_CXX23(std::abs(-1.0L) == 1.0L);

ASSERT_CONSTEXPR_CXX23(std::labs(-1L) == 1L);
ASSERT_CONSTEXPR_CXX23(std::llabs(-1LL) == 1LL);
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30 changes: 19 additions & 11 deletions libcxx/test/std/numerics/c.math/abs.pass.cpp
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Expand Up @@ -20,21 +20,29 @@ struct correct_size_int {
};

template <class Source, class Result>
void test_abs() {
Source neg_val = -5;
Source pos_val = 5;
Result res = 5;
TEST_CONSTEXPR_CXX23 void test_abs() {
TEST_CONSTEXPR_CXX23 Source neg_val = -5;
TEST_CONSTEXPR_CXX23 Source pos_val = 5;
TEST_CONSTEXPR_CXX23 Result res = 5;

ASSERT_SAME_TYPE(decltype(std::abs(neg_val)), Result);

assert(std::abs(neg_val) == res);
assert(std::abs(pos_val) == res);
#if TEST_STD_VER >= 23
static_assert(std::abs(neg_val) == res);
static_assert(std::abs(pos_val) == res);
#else
assert(std::abs(neg_val) == res);
assert(std::abs(pos_val) == res);
#endif
}

void test_big() {
long long int big_value = std::numeric_limits<long long int>::max(); // a value too big for ints to store
long long int negative_big_value = -big_value;
assert(std::abs(negative_big_value) == big_value); // make sure it doesn't get casted to a smaller type
TEST_CONSTEXPR_CXX23 void test_big() {
TEST_CONSTEXPR_CXX23 long long int big_value = std::numeric_limits<long long int>::max(); // a value too big for ints to store
TEST_CONSTEXPR_CXX23 long long int negative_big_value = -big_value;
#if TEST_STD_VER >= 23
static_assert(std::abs(negative_big_value) == big_value); // make sure it doesn't get casted to a smaller type
#else
assert(std::abs(negative_big_value) == big_value); // make sure it doesn't get casted to a smaller type
#endif
}

// The following is helpful to keep in mind:
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