Index: libcxx/include/numeric
===================================================================
--- libcxx/include/numeric
+++ libcxx/include/numeric
@@ -145,6 +145,7 @@
 #include <iterator>
 #include <limits> // for numeric_limits
 #include <functional>
+#include <cmath> // for isnormal
 #include <version>
 
 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
@@ -552,6 +553,23 @@
 {
     return __a + _VSTD::midpoint(ptrdiff_t(0), __b - __a);
 }
+
+
+template <typename _Tp>
+int __sign(_Tp __val) {
+    return (_Tp(0) < __val) - (__val < _Tp(0));
+}
+
+template <class _Fp>
+_LIBCPP_INLINE_VISIBILITY constexpr
+enable_if_t<is_floating_point_v<_Fp>, _Fp>
+midpoint(_Fp __a, _Fp __b) noexcept
+{
+    return isnormal(__a) && isnormal(__b) 
+       && ((__sign(__a) != __sign(__b)) || ((numeric_limits<_Fp>::max() - abs(__a)) < abs(__b)))
+             ?  __a / 2 + __b / 2
+             : (__a + __b) / 2;
+}
 #endif
 
 _LIBCPP_END_NAMESPACE_STD
Index: libcxx/include/version
===================================================================
--- libcxx/include/version
+++ libcxx/include/version
@@ -58,6 +58,7 @@
 __cpp_lib_incomplete_container_elements                 201505L <forward_list> <list> <vector>
 __cpp_lib_integer_sequence                              201304L <utility>
 __cpp_lib_integral_constant_callable                    201304L <type_traits>
+__cpp_lib_interpolate                                   201902L <numeric>
 __cpp_lib_invoke                                        201411L <functional>
 __cpp_lib_is_aggregate                                  201703L <type_traits>
 __cpp_lib_is_constant_evaluated                         201811L <type_traits>
@@ -222,6 +223,7 @@
 // # define __cpp_lib_destroying_delete                    201806L
 # define __cpp_lib_erase_if                             201811L
 // # define __cpp_lib_generic_unordered_lookup             201811L
+#define __cpp_lib_interpolate                           201902L
 // # define __cpp_lib_is_constant_evaluated                201811L
 // # define __cpp_lib_list_remove_return_type              201806L
 // # define __cpp_lib_ranges                               201811L
Index: libcxx/test/std/language.support/support.limits/support.limits.general/numeric.version.pass.cpp
===================================================================
--- libcxx/test/std/language.support/support.limits/support.limits.general/numeric.version.pass.cpp
+++ libcxx/test/std/language.support/support.limits/support.limits.general/numeric.version.pass.cpp
@@ -16,6 +16,7 @@
 /*  Constant                        Value
     __cpp_lib_gcd_lcm               201606L [C++17]
     __cpp_lib_parallel_algorithm    201603L [C++17]
+    __cpp_lib_interpolate           201902L [C++20]
 */
 
 #include <numeric>
@@ -65,6 +66,13 @@
 
 #elif TEST_STD_VER > 17
 
+# ifndef __cpp_lib_interpolate
+#   error "__cpp_lib_interpolate should be defined in c++2a"
+# endif
+# if __cpp_lib_interpolate != 201902L
+#   error "__cpp_lib_interpolate should have the value 201902L in c++2a"
+# endif
+
 # ifndef __cpp_lib_gcd_lcm
 #   error "__cpp_lib_gcd_lcm should be defined in c++2a"
 # endif
Index: libcxx/test/std/language.support/support.limits/support.limits.general/version.version.pass.cpp
===================================================================
--- libcxx/test/std/language.support/support.limits/support.limits.general/version.version.pass.cpp
+++ libcxx/test/std/language.support/support.limits/support.limits.general/version.version.pass.cpp
@@ -50,6 +50,7 @@
     __cpp_lib_incomplete_container_elements        201505L [C++17]
     __cpp_lib_integer_sequence                     201304L [C++14]
     __cpp_lib_integral_constant_callable           201304L [C++14]
+    __cpp_lib_interpolate                          201902L [C++20]
     __cpp_lib_invoke                               201411L [C++17]
     __cpp_lib_is_aggregate                         201703L [C++17]
     __cpp_lib_is_constant_evaluated                201811L [C++2a]
@@ -1778,6 +1779,13 @@
 #   error "__cpp_lib_integral_constant_callable should have the value 201304L in c++2a"
 # endif
 
+# ifndef __cpp_lib_interpolate
+#   error "__cpp_lib_interpolate should be defined in c++2a"
+# endif
+# if __cpp_lib_interpolate != 201902L
+#   error "__cpp_lib_interpolate should have the value 201902L in c++2a"
+# endif
+
 # ifndef __cpp_lib_invoke
 #   error "__cpp_lib_invoke should be defined in c++2a"
 # endif