[libcxx] Add c++20 <numbers>

[kamleshbhalui]

Summary

Supporting
https://eel.is/c++draft/numbers
https://wg21.link/P0631

[kamleshbhalui]

Added test

[kamleshbhalui]

Cleanup and
Add one more test.

[zoecarver]

Thanks for implementing this.

Please update cxx2a_status.html.

libcxx/include/numbers

81

This needs to be mangled (__value).

85

Why not static_assert(false)? Wouldn't that be more clear?

libcxx/test/std/numerics/numbers/numbers.fail.cpp

19

What's this testing?

[kamleshbhalui]

libcxx/include/numbers

85

in that case static_assert will fail even when this template is not instantiated.

[kamleshbhalui]

libcxx/test/std/numerics/numbers/numbers.fail.cpp

19

this testing is that static assert should fail when other than floating type is used.

[kamleshbhalui]

Thanks for review.
added cxx2a _statu.html

[kamleshbhalui]

changed value to __value

[zoecarver]

Of course, thanks for working on this. LGTM.

(you'll still need a libc++ maintainer's review)

libcxx/include/numbers

85

You're right! I always forget :)

[kamleshbhalui]

ping?

[curdeius]

libcxx/include/numbers

81

Given that it's a C++20 addition, I think that you don't need to use _LIBCPP_CONSTEXPR and directly write constexpr. This remarks concerns other usages below.

82

It would be more readable to call it __false_value or alike, because __value seems too generic.

86

Why Using Capital Letters?

What about unifying a bit static assert messages to match other in libc++?

Examples:

static_assert(is_trivially_copyable<_Tp>::value, "std::atomic<Tp> requires that 'Tp' be a trivially copyable type");
static_assert(__is_cpp17_move_insertable<allocator_type>::value, "The specified type does not meet the requirements of Cpp17MoveInsertible");
static_assert(__bitop_unsigned_integer<_Tp>::value, "__rotl requires unsigned");

Maybe something like "<numbers> header requires a floating-point type" or mentioning the corresponding concept (floating_point)?

libcxx/utils/generate_feature_test_macro_components.py

596

It should be written as int(201907), otherwise it won't work on Python3.

[kamleshbhalui]

Thanks for the review @curdeius.
addressed your concerns.

[curdeius]

Thanks for the fast update!

libcxx/include/numbers

194

Where did you take all the values? Do you have a link to e.g. a math notebook online where you computed all those?

libcxx/test/std/numerics/numbers/numbers.pass.cpp

77

Have you clang-formatted your patch?

[kamleshbhalui]

Thanks for review @curdeius
clang-formatted the diff.
and used http://mpmath.org/ for calculating all constants.

[curdeius]

libcxx/test/std/language.support/support.limits/support.limits.general/version.version.pass.cpp

113

It seems that you formatted a bit too much. I think that you should avoid formatting auto-generated files.

[curdeius]

libcxx/include/numbers

186

Typo: gamma

[curdeius]

libcxx/include/numbers

189

For the verification of the numbers, I'd put links to each sequence, e.g. https://oeis.org/A001620 for gamma.
BTW, it seems to be a difference on the last 5 digits. It seems that the sequence 240240243 has incorrectly repeated 240.

[kamleshbhalui]

Incorporated @curdeius suggestion.

[curdeius]

I've just realized that there is already D77505. You should probably think about helping to incorporate your changes into this other PR and abandon this one.

[kamleshbhalui]

duplicate of D77505

libcxx/docs/FeatureTestMacroTable.rst

.. table:: Current Status
     ``__cpp_lib_generic_unordered_lookup``            *unimplemented*  
     ------------------------------------------------- -----------------
     ``__cpp_lib_interpolate``                         ``201902L``      
     ------------------------------------------------- -----------------
     ``__cpp_lib_is_constant_evaluated``               ``201811L``      
     ------------------------------------------------- -----------------
     ``__cpp_lib_list_remove_return_type``             ``201806L``      
     ------------------------------------------------- -----------------
+    ``__cpp_lib_math_constants``                      ``201907L``      
+    ------------------------------------------------- -----------------
     ``__cpp_lib_ranges``                              *unimplemented*  
     ------------------------------------------------- -----------------
     ``__cpp_lib_three_way_comparison``                *unimplemented*  
     ------------------------------------------------- -----------------
     ``__cpp_lib_to_array``                            ``201907L``      
     ================================================= =================
 
 

libcxx/include/CMakeLists.txt

set(files
   locale.h
   map
   math.h
   memory
   module.modulemap
   mutex
   new
   numeric
+  numbers
   optional
   ostream
   queue
   random
   ratio
   regex
   scoped_allocator
   semaphore

libcxx/include/module.modulemap

module std [system] {
   module new {
     header "new"
     export *
   }
   module numeric {
     header "numeric"
     export *
   }
+  module numbers {
+    header "numbers"
+    export *
+  }
   module optional {
     header "optional"
     export *
   }
   module ostream {
     header "ostream"
     // FIXME: should re-export ios, streambuf?
     export *

libcxx/include/numbers

+// -*- C++ -*-
+//===---------------------------- numbers ---------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef _LIBCPP_NUMBERS
+#define _LIBCPP_NUMBERS
+
+/*
+    numbers synopsis
+
+namespace std::numbers
+{
+  template<class T> inline constexpr T e_v          = unspecified;
+  template<class T> inline constexpr T log2e_v      = unspecified;
+  template<class T> inline constexpr T log10e_v     = unspecified;
+  template<class T> inline constexpr T pi_v         = unspecified;
+  template<class T> inline constexpr T inv_pi_v     = unspecified;
+  template<class T> inline constexpr T inv_sqrtpi_v = unspecified;
+  template<class T> inline constexpr T ln2_v        = unspecified;
+  template<class T> inline constexpr T ln10_v       = unspecified;
+  template<class T> inline constexpr T sqrt2_v      = unspecified;
+  template<class T> inline constexpr T sqrt3_v      = unspecified;
+  template<class T> inline constexpr T inv_sqrt3_v  = unspecified;
+  template<class T> inline constexpr T egamma_v     = unspecified;
+  template<class T> inline constexpr T phi_v        = unspecified;
+
+  template<floating_point T> inline constexpr T e_v<T>          = see below;
+  template<floating_point T> inline constexpr T log2e_v<T>      = see below;
+  template<floating_point T> inline constexpr T log10e_v<T>     = see below;
+  template<floating_point T> inline constexpr T pi_v<T>         = see below;
+  template<floating_point T> inline constexpr T inv_pi_v<T>     = see below;
+  template<floating_point T> inline constexpr T inv_sqrtpi_v<T> = see below;
+  template<floating_point T> inline constexpr T ln2_v<T>        = see below;
+  template<floating_point T> inline constexpr T ln10_v<T>       = see below;
+  template<floating_point T> inline constexpr T sqrt2_v<T>      = see below;
+  template<floating_point T> inline constexpr T sqrt3_v<T>      = see below;
+  template<floating_point T> inline constexpr T inv_sqrt3_v<T>  = see below;
+  template<floating_point T> inline constexpr T egamma_v<T>     = see below;
+  template<floating_point T> inline constexpr T phi_v<T>        = see below;
+
+  inline constexpr double e          = e_v<double>;
+  inline constexpr double log2e      = log2e_v<double>;
+  inline constexpr double log10e     = log10e_v<double>;
+  inline constexpr double pi         = pi_v<double>;
+  inline constexpr double inv_pi     = inv_pi_v<double>;
+  inline constexpr double inv_sqrtpi = inv_sqrtpi_v<double>;
+  inline constexpr double ln2        = ln2_v<double>;
+  inline constexpr double ln10       = ln10_v<double>;
+  inline constexpr double sqrt2      = sqrt2_v<double>;
+  inline constexpr double sqrt3      = sqrt3_v<double>;
+  inline constexpr double inv_sqrt3  = inv_sqrt3_v<double>;
+  inline constexpr double egamma     = egamma_v<double>;
+  inline constexpr double phi        = phi_v<double>;
+}  // std::numbers
+
+*/
+
+#include <__config>
+#include <type_traits>
+
+#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
+#pragma GCC system_header
+#endif
+
+_LIBCPP_PUSH_MACROS
+#include <__undef_macros>
+
+_LIBCPP_BEGIN_NAMESPACE_STD
+
+#if _LIBCPP_STD_VER > 17
+
+namespace numbers {
+
+template<class>
+inline constexpr bool __false_value = false;
+
+template<class T>
+constexpr T _AlwaysFalse() {
+   static_assert(__false_value<T>, "<numbers> header requires floating point types");
+   return T();
+}
+
+template<class T>
+inline constexpr T e_v          = _AlwaysFalse<T>();
+
+template<class T>
+inline constexpr T log2e_v      = _AlwaysFalse<T>();
+
+template<class T>
+inline constexpr T log10e_v     = _AlwaysFalse<T>();
+
+template<class T>
+inline constexpr T pi_v         = _AlwaysFalse<T>();
+
+template<class T>
+inline constexpr T inv_pi_v     = _AlwaysFalse<T>();
+
+template<class T>
+inline constexpr T inv_sqrtpi_v = _AlwaysFalse<T>();
+
+template<class T>
+inline constexpr T ln2_v        = _AlwaysFalse<T>();
+
+template<class T>
+inline constexpr T ln10_v       = _AlwaysFalse<T>();
+
+template<class T>
+inline constexpr T sqrt2_v      = _AlwaysFalse<T>();
+
+template<class T>
+inline constexpr T sqrt3_v      = _AlwaysFalse<T>();
+
+template<class T>
+inline constexpr T inv_sqrt3_v  = _AlwaysFalse<T>();
+
+template<class T>
+inline constexpr T egamma_v     = _AlwaysFalse<T>();
+
+template<class T>
+inline constexpr T phi_v        = _AlwaysFalse<T>();
+
+template<typename T>
+concept floating_point = is_floating_point_v<T>;
+
+// https://oeis.org/A001113
+// e
+template<floating_point T>
+inline constexpr
+T e_v<T> = T(2.718281828459045235360287471352662498L);
+
+// https://oeis.org/A007525
+// log2(e)
+template<floating_point T>
+inline constexpr
+T log2e_v<T> = T(1.442695040888963407359924681001892137L);
+
+// https://oeis.org/A002285
+// log10(e)
+template<floating_point T>
+inline constexpr
+T log10e_v<T> = T(0.434294481903251827651128918916605082L);
+
+// https://oeis.org/A000796
+// pi
+template<floating_point T>
+inline constexpr
+T pi_v<T> = T(3.141592653589793238462643383279502884L);
+
+// https://oeis.org/A049541
+// 1/pi
+template<floating_point T>
+inline constexpr
+T inv_pi_v<T> = T(0.318309886183790671537767526745028724L);
+
+// https://oeis.org/A087197
+// 1/sqrt(pi)
+template<floating_point T>
+inline constexpr
+T inv_sqrtpi_v<T> = T(0.564189583547756286948079451560772586L);
+
+// https://oeis.org/A002162
+// log_e(2)
+template<floating_point T>
+inline constexpr
+T ln2_v<T> = T(0.693147180559945309417232121458176568L);
+
+// https://oeis.org/A002392
+// log_e(10)
+template<floating_point T>
+inline constexpr
+T ln10_v<T> = T(2.3025850929940456840179914546843642087L);
+
+// https://oeis.org/A002193
+// sqrt(2)
+template<floating_point T>
+inline constexpr
+T sqrt2_v<T> = T(1.414213562373095048801688724209698078L);
+
+// https://oeis.org/A002194
+// sqrt(3)
+template<floating_point T>
+inline constexpr
+T sqrt3_v<T> = T(1.732050807568877293527446341505872366L);
+
+// https://oeis.org/A020760
+// 1/sqrt(3)
+template<floating_point T>
+inline constexpr
+T inv_sqrt3_v<T> = T(0.577350269189625764509148780501957456L);
+
+// https://oeis.org/A001620
+// Euler-Mascheroni gamma constant
+template<floating_point T>
+inline constexpr
+T egamma_v<T> = T(0.577215664901532860606512090082402431L);
+
+// https://oeis.org/A001622
+// Golden ratio phi constant
+template<floating_point T>
+inline constexpr
+T phi_v<T> = T(1.618033988749894848204586834365638117L);
+
+
+inline constexpr double e          = e_v<double>;
+inline constexpr double log2e      = log2e_v<double>;
+inline constexpr double log10e     = log10e_v<double>;
+inline constexpr double pi         = pi_v<double>;
+inline constexpr double inv_pi     = inv_pi_v<double>;
+inline constexpr double inv_sqrtpi = inv_sqrtpi_v<double>;
+inline constexpr double ln2        = ln2_v<double>;
+inline constexpr double ln10       = ln10_v<double>;
+inline constexpr double sqrt2      = sqrt2_v<double>;
+inline constexpr double sqrt3      = sqrt3_v<double>;
+inline constexpr double inv_sqrt3  = inv_sqrt3_v<double>;
+inline constexpr double egamma     = egamma_v<double>;
+inline constexpr double phi        = phi_v<double>;
+} //namespace numbers
+
+#endif //_LIBCPP_STD_VER > 17
+
+_LIBCPP_END_NAMESPACE_STD
+
+_LIBCPP_POP_MACROS
+
+#endif  //_LIBCPP_NUMBERS

libcxx/include/version

 __cpp_lib_is_swappable                                  201603L <type_traits>
 __cpp_lib_launder                                       201606L <new>
 __cpp_lib_list_remove_return_type                       201806L <forward_list> <list>
 __cpp_lib_logical_traits                                201510L <type_traits>
 __cpp_lib_make_from_tuple                               201606L <tuple>
 __cpp_lib_make_reverse_iterator                         201402L <iterator>
 __cpp_lib_make_unique                                   201304L <memory>
 __cpp_lib_map_try_emplace                               201411L <map>
+__cpp_lib_math_constants                                201907L <numbers>
 __cpp_lib_math_special_functions                        201603L <cmath>
 __cpp_lib_memory_resource                               201603L <memory_resource>
 __cpp_lib_node_extract                                  201606L <map> <set> <unordered_map>
                                                                 <unordered_set>
 __cpp_lib_nonmember_container_access                    201411L <iterator> <array> <deque>
                                                                 <forward_list> <list> <map>
                                                                 <regex> <set> <string>
                                                                 <unordered_map> <unordered_set> <vector>

 # define __cpp_lib_endian                               201907L
 # define __cpp_lib_erase_if                             202002L
 // # define __cpp_lib_generic_unordered_lookup             201811L
 # define __cpp_lib_interpolate                          201902L
 # if !defined(_LIBCPP_HAS_NO_BUILTIN_IS_CONSTANT_EVALUATED)
 #   define __cpp_lib_is_constant_evaluated              201811L
 # endif
 # define __cpp_lib_list_remove_return_type              201806L
+# define __cpp_lib_math_constants                       201907L
 // # define __cpp_lib_ranges                               201811L
-# define __cpp_lib_to_array                                201907L
 // # define __cpp_lib_three_way_comparison                 201711L
+# define __cpp_lib_to_array                             201907L
 #endif
 
 #endif // _LIBCPP_VERSIONH

libcxx/test/libcxx/double_include.sh.cpp

 #include <map>
 #include <math.h>
 #include <memory>
 #ifndef _LIBCPP_HAS_NO_THREADS
 #include <mutex>
 #endif
 #include <new>
 #include <numeric>
+#include <numbers>
 #include <optional>
 #include <ostream>
 #include <queue>
 #include <random>
 #include <ratio>
 #include <regex>
 #include <scoped_allocator>
 #include <set>

libcxx/test/std/language.support/support.limits/support.limits.general/numbers.version.pass.cpp

+//===----------------------------------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+//
+// WARNING: This test was generated by generate_feature_test_macro_components.py
+// and should not be edited manually.
+
+// <numbers>
+
+// Test the feature test macros defined by <numbers>
+
+/*  Constant                    Value
+    __cpp_lib_math_constants    201907L [C++2a]
+*/
+
+#include <numbers>
+#include "test_macros.h"
+
+#if TEST_STD_VER < 14
+
+# ifdef __cpp_lib_math_constants
+#   error "__cpp_lib_math_constants should not be defined before c++2a"
+# endif
+
+#elif TEST_STD_VER == 14
+
+# ifdef __cpp_lib_math_constants
+#   error "__cpp_lib_math_constants should not be defined before c++2a"
+# endif
+
+#elif TEST_STD_VER == 17
+
+# ifdef __cpp_lib_math_constants
+#   error "__cpp_lib_math_constants should not be defined before c++2a"
+# endif
+
+#elif TEST_STD_VER > 17
+
+# ifndef __cpp_lib_math_constants
+#   error "__cpp_lib_math_constants should be defined in c++2a"
+# endif
+# if __cpp_lib_math_constants != 201907L
+#   error "__cpp_lib_math_constants should have the value 201907L in c++2a"
+# endif
+
+#endif // TEST_STD_VER > 17
+
+int main(int, char**) { return 0; }

libcxx/test/std/language.support/support.limits/support.limits.general/version.version.pass.cpp

/*  Constant                                       Value
     __cpp_lib_is_swappable                         201603L [C++17]
     __cpp_lib_launder                              201606L [C++17]
     __cpp_lib_list_remove_return_type              201806L [C++2a]
     __cpp_lib_logical_traits                       201510L [C++17]
     __cpp_lib_make_from_tuple                      201606L [C++17]
     __cpp_lib_make_reverse_iterator                201402L [C++14]
     __cpp_lib_make_unique                          201304L [C++14]
     __cpp_lib_map_try_emplace                      201411L [C++17]
+    __cpp_lib_math_constants                       201907L [C++2a]
     __cpp_lib_math_special_functions               201603L [C++17]
     __cpp_lib_memory_resource                      201603L [C++17]
     __cpp_lib_node_extract                         201606L [C++17]
     __cpp_lib_nonmember_container_access           201411L [C++17]
     __cpp_lib_not_fn                               201603L [C++17]
     __cpp_lib_null_iterators                       201304L [C++14]
     __cpp_lib_optional                             201606L [C++17]
     __cpp_lib_parallel_algorithm                   201603L [C++17]

 
 #include <version>
 #include "test_macros.h"
 
 #if TEST_STD_VER < 14
 
 # ifdef __cpp_lib_addressof_constexpr
 #   error "__cpp_lib_addressof_constexpr should not be defined before c++17"
 # endif
 
 # ifdef __cpp_lib_allocator_traits_is_always_equal
 #   error "__cpp_lib_allocator_traits_is_always_equal should not be defined before c++17"
 # endif
 
 # ifdef __cpp_lib_any
 #   error "__cpp_lib_any should not be defined before c++17"
 # endif

 # ifdef __cpp_lib_make_unique
 #   error "__cpp_lib_make_unique should not be defined before c++14"
 # endif
 
 # ifdef __cpp_lib_map_try_emplace
 #   error "__cpp_lib_map_try_emplace should not be defined before c++17"
 # endif
 
+# ifdef __cpp_lib_math_constants
+#   error "__cpp_lib_math_constants should not be defined before c++2a"
+# endif
+
 # ifdef __cpp_lib_math_special_functions
 #   error "__cpp_lib_math_special_functions should not be defined before c++17"
 # endif
 
 # ifdef __cpp_lib_memory_resource
 #   error "__cpp_lib_memory_resource should not be defined before c++17"
 # endif
 

 # if __cpp_lib_make_unique != 201304L
 #   error "__cpp_lib_make_unique should have the value 201304L in c++14"
 # endif
 
 # ifdef __cpp_lib_map_try_emplace
 #   error "__cpp_lib_map_try_emplace should not be defined before c++17"
 # endif
 
+# ifdef __cpp_lib_math_constants
+#   error "__cpp_lib_math_constants should not be defined before c++2a"
+# endif
+
 # ifdef __cpp_lib_math_special_functions
 #   error "__cpp_lib_math_special_functions should not be defined before c++17"
 # endif
 
 # ifdef __cpp_lib_memory_resource
 #   error "__cpp_lib_memory_resource should not be defined before c++17"
 # endif
 

 
 # ifndef __cpp_lib_map_try_emplace
 #   error "__cpp_lib_map_try_emplace should be defined in c++17"
 # endif
 # if __cpp_lib_map_try_emplace != 201411L
 #   error "__cpp_lib_map_try_emplace should have the value 201411L in c++17"
 # endif
 
+# ifdef __cpp_lib_math_constants
+#   error "__cpp_lib_math_constants should not be defined before c++2a"
+# endif
+
 # if !defined(_LIBCPP_VERSION)
 #   ifndef __cpp_lib_math_special_functions
 #     error "__cpp_lib_math_special_functions should be defined in c++17"
 #   endif
 #   if __cpp_lib_math_special_functions != 201603L
 #     error "__cpp_lib_math_special_functions should have the value 201603L in c++17"
 #   endif
 # else // _LIBCPP_VERSION

 
 # ifndef __cpp_lib_map_try_emplace
 #   error "__cpp_lib_map_try_emplace should be defined in c++2a"
 # endif
 # if __cpp_lib_map_try_emplace != 201411L
 #   error "__cpp_lib_map_try_emplace should have the value 201411L in c++2a"
 # endif
 
+# ifndef __cpp_lib_math_constants
+#   error "__cpp_lib_math_constants should be defined in c++2a"
+# endif
+# if __cpp_lib_math_constants != 201907L
+#   error "__cpp_lib_math_constants should have the value 201907L in c++2a"
+# endif
+
 # if !defined(_LIBCPP_VERSION)
 #   ifndef __cpp_lib_math_special_functions
 #     error "__cpp_lib_math_special_functions should be defined in c++2a"
 #   endif
 #   if __cpp_lib_math_special_functions != 201603L
 #     error "__cpp_lib_math_special_functions should have the value 201603L in c++2a"
 #   endif
 # else // _LIBCPP_VERSION

libcxx/test/std/numerics/numbers/numbers.fail.cpp

+//===----------------------------------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+// UNSUPPORTED: c++98, c++03, c++11, c++14, c++17
+
+#include <numbers>
+#include "test_macros.h"
+struct S1 {};
+int main() {
+
+  constexpr int d = std::numbers::e_v<
+      int>; // expected-error-re@numbers:* {{static_assert failed{{( due to requirement '.*')?}}}}
+  constexpr S1 s = std::numbers::e_v<
+      S1>; // expected-error-re@numbers:* {{static_assert failed{{( due to requirement '.*')?}}}}
+  return 0;
+}

libcxx/test/std/numerics/numbers/numbers.pass.cpp

+//===----------------------------------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+// UNSUPPORTED: c++98, c++03, c++11, c++14, c++17
+
+#include <numbers>
+#include "test_macros.h"
+
+int main() {
+
+  // float
+  constexpr float f = std::numbers::e_v<float>;
+  constexpr float f1 = std::numbers::log2e_v<float>;
+  constexpr float f2 = std::numbers::log10e_v<float>;
+  constexpr float f3 = std::numbers::pi_v<float>;
+  constexpr float f4 = std::numbers::inv_pi_v<float>;
+  constexpr float f5 = std::numbers::inv_sqrtpi_v<float>;
+  constexpr float f6 = std::numbers::ln2_v<float>;
+  constexpr float f7 = std::numbers::ln10_v<float>;
+  constexpr float f8 = std::numbers::sqrt2_v<float>;
+  constexpr float f9 = std::numbers::sqrt3_v<float>;
+  constexpr float f10 = std::numbers::inv_sqrt3_v<float>;
+  constexpr float f11 = std::numbers::egamma_v<float>;
+  constexpr float f12 = std::numbers::phi_v<float>;
+
+  // double
+  constexpr double d = std::numbers::e_v<double>;
+  constexpr double d1 = std::numbers::log2e_v<double>;
+  constexpr double d2 = std::numbers::log10e_v<double>;
+  constexpr double d3 = std::numbers::pi_v<double>;
+  constexpr double d4 = std::numbers::inv_pi_v<double>;
+  constexpr double d5 = std::numbers::inv_sqrtpi_v<double>;
+  constexpr double d6 = std::numbers::ln2_v<double>;
+  constexpr double d7 = std::numbers::ln10_v<double>;
+  constexpr double d8 = std::numbers::sqrt2_v<double>;
+  constexpr double d9 = std::numbers::sqrt3_v<double>;
+  constexpr double d10 = std::numbers::inv_sqrt3_v<double>;
+  constexpr double d11 = std::numbers::egamma_v<double>;
+  constexpr double d12 = std::numbers::phi_v<double>;
+  // static assert checks
+  static_assert(d == std::numbers::e, "d != std::numbers::e ");
+  static_assert(d1 == std::numbers::log2e, "d1 != std::numbers::log2e");
+  static_assert(d2 == std::numbers::log10e, "d2 != std::numbers::log10e");
+  static_assert(d3 == std::numbers::pi, "d3 != std::numbers::pi");
+  static_assert(d4 == std::numbers::inv_pi, "d4 != std::numbers::inv_pi");
+  static_assert(d5 == std::numbers::inv_sqrtpi,
+                "d5 != std::numbers::inv_sqrtpi");
+  static_assert(d6 == std::numbers::ln2, "d6 != std::numbers::ln2");
+  static_assert(d7 == std::numbers::ln10, "d7 != std::numbers::ln10");
+  static_assert(d8 == std::numbers::sqrt2, "d8 != std::numbers::sqrt2");
+  static_assert(d9 == std::numbers::sqrt3, "d9 != std::numbers::sqrt3");
+  static_assert(d10 == std::numbers::inv_sqrt3,
+                "d10 != std::numbers::inv_sqrt3");
+  static_assert(d11 == std::numbers::egamma, "d11 != std::numbers::egamma");
+  static_assert(d12 == std::numbers::phi, "d12 != std::numbers::phi");
+  // long oduble
+  constexpr long double ld = std::numbers::e_v<long double>;
+  constexpr long double ld1 = std::numbers::log2e_v<long double>;
+  constexpr long double ld2 = std::numbers::log10e_v<long double>;
+  constexpr long double ld3 = std::numbers::pi_v<long double>;
+  constexpr long double ld4 = std::numbers::inv_pi_v<long double>;
+  constexpr long double ld5 = std::numbers::inv_sqrtpi_v<long double>;
+  constexpr long double ld6 = std::numbers::ln2_v<long double>;
+  constexpr long double ld7 = std::numbers::ln10_v<long double>;
+  constexpr long double ld8 = std::numbers::sqrt2_v<long double>;
+  constexpr long double ld9 = std::numbers::sqrt3_v<long double>;
+  constexpr long double ld10 = std::numbers::inv_sqrt3_v<long double>;
+  constexpr long double ld11 = std::numbers::egamma_v<long double>;
+  constexpr long double ld12 = std::numbers::phi_v<long double>;
+
+  return 0;
+}

libcxx/utils/generate_feature_test_macro_components.py

feature_test_macros = sorted([ add_version_header(x) for x in [
    "headers": ["bit"],
    },
   {"name": "__cpp_lib_to_array",
    "values": {
      "c++2a": int(201907),
    },
    "headers": ["array"],
    },
+  {"name": "__cpp_lib_math_constants",
+   "values": {
+     "c++2a": int(201907),
+   },
+   "headers": ["numbers"],
+   },
 ]], key=lambda tc: tc["name"])
 
 def get_std_dialects():
   std_dialects = ['c++14', 'c++17', 'c++2a']
   return list(std_dialects)
 
 def get_first_std(d):
     for s in get_std_dialects():

libcxx/www/cxx2a_status.html

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