use stl numbers

Author: gouarin

include/xtensor/core/xmath.hpp

@@ -18,6 +18,7 @@
 #include <array>
 #include <cmath>
 #include <complex>
+#include <numbers>
 #include <type_traits>
 
 #include <xtl/xcomplex.hpp>
@@ -38,18 +39,18 @@ namespace xt
     template <class T = double>
     struct numeric_constants
     {
-        static constexpr T PI = 3.141592653589793238463;
-        static constexpr T PI_2 = 1.57079632679489661923;
-        static constexpr T PI_4 = 0.785398163397448309616;
-        static constexpr T D_1_PI = 0.318309886183790671538;
-        static constexpr T D_2_PI = 0.636619772367581343076;
-        static constexpr T D_2_SQRTPI = 1.12837916709551257390;
-        static constexpr T SQRT2 = 1.41421356237309504880;
-        static constexpr T SQRT1_2 = 0.707106781186547524401;
-        static constexpr T E = 2.71828182845904523536;
-        static constexpr T LOG2E = 1.44269504088896340736;
-        static constexpr T LOG10E = 0.434294481903251827651;
-        static constexpr T LN2 = 0.693147180559945309417;
+        static constexpr T PI = std::numbers::pi_v<T>;
+        static constexpr T PI_2 = 0.5*PI;
+        static constexpr T PI_4 = 0.25*PI;
+        static constexpr T D_1_PI = std::numbers::inv_pi_v<T>;
+        static constexpr T D_2_PI = 2*std::numbers::inv_pi_v<T>;
+        static constexpr T D_2_SQRTPI = 2*std::numbers::inv_sqrtpi_v<T>;
+        static constexpr T SQRT2 = std::numbers::sqrt2_v<T>;
+        static constexpr T SQRT1_2 = 0.5*std::numbers::sqrt2_v<T>;
+        static constexpr T E = std::numbers::e_v<T>;
+        static constexpr T LOG2E = std::numbers::log2e_v<T>;
+        static constexpr T LOG10E = std::numbers::log10e_v<T>;
+        static constexpr T LN2 = std::numbers::ln2_v<T>;
     };
 
     /***********