Constexpr hypot (#721)

doc/sf/ccmath.qbk

@@ -143,6 +143,12 @@ All of the following functions require C++17 or greater.
         template <typename Arithmetic1, typename Arithmetic2>
         inline constexpr Promoted copysign(Arithmetic1 mag, Arithmetic2 sgn) noexcept
 
+        template <typename Real>
+        inline constexpr Real hypot(Real x, Real y) noexcept
+
+        template <typename Arithmetic1, typename Arithmetic2>
+        inline constexpr Promoted hypot(Arithmetic1 x, Arithmetic2 y) noexcept
+
     } // Namespaces
 
 [endsect] [/section:ccmath Constexpr CMath]

include/boost/math/ccmath/ccmath.hpp

@@ -29,5 +29,6 @@
 #include <boost/math/ccmath/fmod.hpp>
 #include <boost/math/ccmath/remainder.hpp>
 #include <boost/math/ccmath/copysign.hpp>
+#include <boost/math/ccmath/hypot.hpp>
 
 #endif // BOOST_MATH_CCMATH_HPP

include/boost/math/ccmath/detail/swap.hpp

@@ -0,0 +1,21 @@
+//  (C) Copyright Matt Borland 2021.
+//  Use, modification and distribution are subject to the
+//  Boost Software License, Version 1.0. (See accompanying file
+//  LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+
+#ifndef BOOST_MATH_CCMATH_DETAIL_SWAP_HPP
+#define BOOST_MATH_CCMATH_DETAIL_SWAP_HPP
+
+namespace boost::math::ccmath::detail {
+
+template <typename T>
+inline constexpr void swap(T& x, T& y) noexcept
+{
+    T temp = x;
+    x = y;
+    y = temp;
+}
+
+}
+
+#endif // BOOST_MATH_CCMATH_DETAIL_SWAP_HPP

include/boost/math/ccmath/hypot.hpp

@@ -0,0 +1,114 @@
+//  (C) Copyright John Maddock 2005-2021.
+//  (C) Copyright Matt Borland 2021.
+//  Use, modification and distribution are subject to the
+//  Boost Software License, Version 1.0. (See accompanying file
+//  LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+
+#ifndef BOOST_MATH_CCMATH_HYPOT_HPP
+#define BOOST_MATH_CCMATH_HYPOT_HPP
+
+#include <cmath>
+#include <array>
+#include <limits>
+#include <type_traits>
+#include <boost/math/tools/config.hpp>
+#include <boost/math/tools/is_constant_evaluated.hpp>
+#include <boost/math/ccmath/sqrt.hpp>
+#include <boost/math/ccmath/abs.hpp>
+#include <boost/math/ccmath/isinf.hpp>
+#include <boost/math/ccmath/isnan.hpp>
+#include <boost/math/ccmath/detail/swap.hpp>
+
+namespace boost::math::ccmath {
+
+namespace detail {
+
+template <typename T>
+inline constexpr T hypot_impl(T x, T y) noexcept
+{
+    x = boost::math::ccmath::abs(x);
+    y = boost::math::ccmath::abs(y);
+
+    if (y > x)
+    {
+        boost::math::ccmath::detail::swap(x, y);
+    }
+
+    if(x * std::numeric_limits<T>::epsilon() >= y)
+    {
+        return x;
+    }
+
+    T rat = y / x;
+    return x * boost::math::ccmath::sqrt(1 + rat * rat);
+}
+
+} // Namespace detail
+
+template <typename Real, std::enable_if_t<!std::is_integral_v<Real>, bool> = true>
+inline constexpr Real hypot(Real x, Real y) noexcept
+{
+    if(BOOST_MATH_IS_CONSTANT_EVALUATED(x))
+    {
+        return boost::math::ccmath::abs(x) == Real(0) ? boost::math::ccmath::abs(y) :
+               boost::math::ccmath::abs(y) == Real(0) ? boost::math::ccmath::abs(x) :
+               boost::math::ccmath::isinf(x) ? std::numeric_limits<Real>::infinity() :
+               boost::math::ccmath::isinf(y) ? std::numeric_limits<Real>::infinity() :
+               boost::math::ccmath::isnan(x) ? std::numeric_limits<Real>::quiet_NaN() :
+               boost::math::ccmath::isnan(y) ? std::numeric_limits<Real>::quiet_NaN() :
+               boost::math::ccmath::detail::hypot_impl(x, y);
+    }
+    else
+    {
+        using std::hypot;
+        return hypot(x, y);
+    }
+}
+
+template <typename T1, typename T2>
+inline constexpr auto hypot(T1 x, T2 y) noexcept
+{
+    if(BOOST_MATH_IS_CONSTANT_EVALUATED(x))
+    {
+        // If the type is an integer (e.g. epsilon == 0) then set the epsilon value to 1 so that type is at a minimum 
+        // cast to double
+        constexpr auto T1p = std::numeric_limits<T1>::epsilon() > 0 ? std::numeric_limits<T1>::epsilon() : 1;
+        constexpr auto T2p = std::numeric_limits<T2>::epsilon() > 0 ? std::numeric_limits<T2>::epsilon() : 1;
+        
+        using promoted_type = 
+                              #ifndef BOOST_MATH_NO_LONG_DOUBLE_MATH_FUNCTIONS
+                              std::conditional_t<T1p <= LDBL_EPSILON && T1p <= T2p, T1,
+                              std::conditional_t<T2p <= LDBL_EPSILON && T2p <= T1p, T2,
+                              #endif
+                              std::conditional_t<T1p <= DBL_EPSILON && T1p <= T2p, T1,
+                              std::conditional_t<T2p <= DBL_EPSILON && T2p <= T1p, T2, double
+                              #ifndef BOOST_MATH_NO_LONG_DOUBLE_MATH_FUNCTIONS
+                              >>>>;
+                              #else
+                              >>;
+                              #endif
+
+        return boost::math::ccmath::hypot(promoted_type(x), promoted_type(y));
+    }
+    else
+    {
+        using std::hypot;
+        return hypot(x, y);
+    }
+}
+
+inline constexpr float hypotf(float x, float y) noexcept
+{
+    return boost::math::ccmath::hypot(x, y);
+}
+
+#ifndef BOOST_MATH_NO_LONG_DOUBLE_MATH_FUNCTIONS
+inline constexpr long double hypotl(long double x, long double y) noexcept
+{
+    return boost::math::ccmath::hypot(x, y);
+}
+#endif
+
+} // Namespaces
+
+#endif // BOOST_MATH_CCMATH_HYPOT_HPP

test/Jamfile.v2

@@ -143,6 +143,7 @@ test-suite special_fun :
    [ run ccmath_fmod_test.cpp ../../test/build//boost_unit_test_framework : : : [ requires cxx17_if_constexpr ] ]
    [ run ccmath_remainder_test.cpp ../../test/build//boost_unit_test_framework : : : [ requires cxx17_if_constexpr ] ]
    [ run ccmath_copysign_test.cpp ../../test/build//boost_unit_test_framework : : : [ requires cxx17_if_constexpr ] ]
+   [ run ccmath_hypot_test.cpp ../../test/build//boost_unit_test_framework : : : [ requires cxx17_if_constexpr ] ]
    [ run log1p_expm1_test.cpp test_instances//test_instances pch_light ../../test/build//boost_unit_test_framework  ]
    [ run powm1_sqrtp1m1_test.cpp test_instances//test_instances pch_light ../../test/build//boost_unit_test_framework  ]
    [ run special_functions_test.cpp ../../test/build//boost_unit_test_framework  ]

test/ccmath_hypot_test.cpp

@@ -0,0 +1,77 @@
+//  (C) Copyright Matt Borland 2021.
+//  Use, modification and distribution are subject to the
+//  Boost Software License, Version 1.0. (See accompanying file
+//  LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+
+#include <cmath>
+#include <cfloat>
+#include <cstdint>
+#include <limits>
+#include <type_traits>
+#include <boost/math/ccmath/hypot.hpp>
+#include <boost/math/ccmath/isnan.hpp>
+#include <boost/math/ccmath/isinf.hpp>
+#include <boost/math/ccmath/sqrt.hpp>
+
+#ifdef BOOST_HAS_FLOAT128
+#include <boost/multiprecision/float128.hpp>
+#endif
+
+#if !defined(BOOST_MATH_NO_CONSTEXPR_DETECTION) && !defined(BOOST_MATH_USING_BUILTIN_CONSTANT_P)
+template <typename T>
+constexpr void test()
+{
+    // Error Handling
+    if constexpr (std::numeric_limits<T>::has_quiet_NaN)
+    {
+        static_assert(boost::math::ccmath::isnan(boost::math::ccmath::hypot(std::numeric_limits<T>::quiet_NaN(), T(1))), "If x is NaN, NaN is returned");
+        static_assert(boost::math::ccmath::isnan(boost::math::ccmath::hypot(T(1), std::numeric_limits<T>::quiet_NaN())), "If y is NaN, NaN is returned");
+    }
+
+    static_assert(boost::math::ccmath::isinf(boost::math::ccmath::hypot(std::numeric_limits<T>::infinity(), T(1))));
+    static_assert(boost::math::ccmath::isinf(boost::math::ccmath::hypot(-std::numeric_limits<T>::infinity(), T(1))));
+    static_assert(boost::math::ccmath::isinf(boost::math::ccmath::hypot(T(1), std::numeric_limits<T>::infinity())));
+    static_assert(boost::math::ccmath::isinf(boost::math::ccmath::hypot(T(1), -std::numeric_limits<T>::infinity())));
+
+    // Correct promoted types
+    if constexpr (!std::is_same_v<T, float>)
+    {
+        constexpr auto test_type = boost::math::ccmath::hypot(T(1), 1.0f);
+        static_assert(std::is_same_v<T, std::remove_cv_t<decltype(test_type)>>);
+    }
+    else
+    {
+        constexpr auto test_type = boost::math::ccmath::hypot(1.0f, 1);
+        static_assert(std::is_same_v<double, std::remove_cv_t<decltype(test_type)>>);
+    }
+
+    // Functionality
+    static_assert(boost::math::ccmath::hypot(T(1), T(1)) == boost::math::ccmath::sqrt(T(2)));
+    static_assert(boost::math::ccmath::hypot(T(-1), T(1)) == boost::math::ccmath::sqrt(T(2)));
+    static_assert(boost::math::ccmath::hypot(T(-1), T(-1)) == boost::math::ccmath::sqrt(T(2)));
+    static_assert(boost::math::ccmath::hypot(T(1), T(-1)) == boost::math::ccmath::sqrt(T(2)));
+    static_assert(boost::math::ccmath::hypot(T(1), T(2)) == boost::math::ccmath::sqrt(T(5)));
+    static_assert(boost::math::ccmath::hypot(T(2), T(2)) == boost::math::ccmath::sqrt(T(8)));
+}
+
+int main()
+{
+    test<float>();
+    test<double>();
+
+    #ifndef BOOST_MATH_NO_LONG_DOUBLE_MATH_FUNCTIONS
+    test<long double>();
+    #endif
+    
+    #ifdef BOOST_HAS_FLOAT128
+    test<boost::multiprecision::float128>();
+    #endif
+
+    return 0;
+}
+#else
+int main()
+{
+    return 0;
+}
+#endif