math_constants.hpp

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#pragma once
 
#include "types.hpp"
#include <numbers>
 
namespace uni20
{
namespace detail
{
template <class T> struct math_constants
{};
 
template <class T>
  requires(std::same_as<T, float> || std::same_as<T, double> || std::same_as<T, long double>
#if UNI20_HAS_FLOAT128
           || std::same_as<T, float128>
#endif
           )
struct math_constants<T>
{
    static constexpr T pi = std::numbers::pi_v<T>;
    static constexpr T log_two = std::numbers::ln2_v<T>;
    static constexpr T euler_gamma = std::numbers::egamma_v<T>;
    // First 128 binary fractional bits, generated with a 512-bit oracle.
    // Integer chunks and binary scales avoid a narrower floating intermediate.
    // The resulting rounding is verified for every configured native format.
    static constexpr T catalan = T(0xea7cb89f409ae845ULL) * T(0x1p-64L) + T(0x215822e37d32d0c6ULL) * T(0x1p-128L);
};
} // namespace detail
 
template <class Real>
  requires requires { detail::math_constants<Real>::pi; }
inline constexpr auto pi = detail::math_constants<Real>::pi;
 
template <class Real>
  requires requires { detail::math_constants<Real>::log_two; }
inline constexpr auto log_two = detail::math_constants<Real>::log_two;
 
template <class Real>
  requires requires { detail::math_constants<Real>::euler_gamma; }
inline constexpr auto euler_gamma = detail::math_constants<Real>::euler_gamma;
 
template <class Real>
  requires requires { detail::math_constants<Real>::catalan; }
inline constexpr auto catalan = detail::math_constants<Real>::catalan;
} // namespace uni20