From 824f03d5f5b4c01fa81e427b2f4f0902b86fb996 Mon Sep 17 00:00:00 2001
From: Matt Borland <matt@mattborland.com>
Date: Mon, 9 Jan 2023 07:38:14 -0800
Subject: [PATCH 1/2] Add 3-arg hypot

---
 include/boost/math/ccmath/hypot.hpp | 63 +++++++++++++++++++++++++++++
 test/ccmath_hypot_test.cpp          | 51 +++++++++++++++++++++++
 2 files changed, 114 insertions(+)

diff --git a/include/boost/math/ccmath/hypot.hpp b/include/boost/math/ccmath/hypot.hpp
index 613b2681ac..2a48a80c59 100644
--- a/include/boost/math/ccmath/hypot.hpp
+++ b/include/boost/math/ccmath/hypot.hpp
@@ -18,6 +18,7 @@
 #include <boost/math/ccmath/abs.hpp>
 #include <boost/math/ccmath/isinf.hpp>
 #include <boost/math/ccmath/isnan.hpp>
+#include <boost/math/ccmath/fmax.hpp>
 #include <boost/math/ccmath/detail/swap.hpp>
 
 namespace boost::math::ccmath {
@@ -44,6 +45,20 @@ constexpr T hypot_impl(T x, T y) noexcept
     return x * boost::math::ccmath::sqrt(1 + rat * rat);
 }
 
+template <typename T>
+constexpr T hypot_impl(T x, T y, T z) noexcept
+{
+    x = boost::math::ccmath::abs(x);
+    y = boost::math::ccmath::abs(y);
+    z = boost::math::ccmath::abs(z);
+
+    T a = boost::math::ccmath::fmax(boost::math::ccmath::fmax(x, y), z);
+
+    return a * boost::math::ccmath::sqrt((x / a) * (x / a) 
+                                       + (y / a) * (y / a) 
+                                       + (z / a) * (z / a));
+}
+
 } // Namespace detail
 
 template <typename Real, std::enable_if_t<!std::is_integral_v<Real>, bool> = true>
@@ -109,6 +124,54 @@ constexpr long double hypotl(long double x, long double y) noexcept
 }
 #endif
 
+template <typename Real, std::enable_if_t<!std::is_integral_v<Real>, bool> = true>
+constexpr auto hypot(Real x, Real y, Real z) noexcept
+{
+    if (BOOST_MATH_IS_CONSTANT_EVALUATED(x))
+    {
+        if (boost::math::ccmath::isinf(x) || boost::math::ccmath::isinf(y) || boost::math::ccmath::isinf(z))
+        {
+            return std::numeric_limits<Real>::infinity();
+        }
+        else if (boost::math::ccmath::isnan(x))
+        {
+            return x;
+        }
+        else if (boost::math::ccmath::isnan(y))
+        {
+            return y;
+        }
+        else if (boost::math::ccmath::isnan(z))
+        {
+            return z;
+        }
+
+        return detail::hypot_impl(x, y, z);
+    }
+    else
+    {
+        using std::hypot;
+        return hypot(x, y, z);
+    }
+}
+
+template <typename T1, typename T2, typename T3>
+constexpr auto hypot(T1 x, T2 y, T3 z) noexcept
+{
+    if (BOOST_MATH_IS_CONSTANT_EVALUATED(x))
+    {
+        using promoted_type = tools::promote_args_t<T1, T2, T3>;
+        return boost::math::ccmath::hypot(static_cast<promoted_type>(x), 
+                                          static_cast<promoted_type>(y), 
+                                          static_cast<promoted_type>(z));
+    }
+    else
+    {
+        using std::hypot;
+        return hypot(x, y, z);
+    }
+}
+
 } // Namespaces
 
 #endif // BOOST_MATH_CCMATH_HYPOT_HPP
diff --git a/test/ccmath_hypot_test.cpp b/test/ccmath_hypot_test.cpp
index bc85b65962..c4cbc32c5d 100644
--- a/test/ccmath_hypot_test.cpp
+++ b/test/ccmath_hypot_test.cpp
@@ -54,6 +54,46 @@ constexpr void test()
     static_assert(boost::math::ccmath::hypot(T(2), T(2)) == boost::math::ccmath::sqrt(T(8)));
 }
 
+template <typename T>
+constexpr void test_3_arg()
+{
+    constexpr T tol = 5 * std::numeric_limits<T>::epsilon();
+    
+    // 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), 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(), T(1))), "If y is NaN, NaN is returned");
+        static_assert(boost::math::ccmath::isnan(boost::math::ccmath::hypot(T(1), T(1), std::numeric_limits<T>::quiet_NaN())), "If z is NaN, NaN is returned");
+    }
+
+    static_assert(boost::math::ccmath::isinf(boost::math::ccmath::hypot(std::numeric_limits<T>::infinity(), T(1), T(1))));
+    static_assert(boost::math::ccmath::isinf(boost::math::ccmath::hypot(-std::numeric_limits<T>::infinity(), T(1), T(1))));
+    static_assert(boost::math::ccmath::isinf(boost::math::ccmath::hypot(T(1), std::numeric_limits<T>::infinity(), T(1))));
+    static_assert(boost::math::ccmath::isinf(boost::math::ccmath::hypot(T(1), -std::numeric_limits<T>::infinity(), T(1))));
+    static_assert(boost::math::ccmath::isinf(boost::math::ccmath::hypot(T(1), T(1), std::numeric_limits<T>::infinity())));
+    static_assert(boost::math::ccmath::isinf(boost::math::ccmath::hypot(T(1), 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), 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, 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), T(1)) == boost::math::ccmath::sqrt(T(3)));
+    static_assert(boost::math::ccmath::hypot(T(-1), T(1), T(1)) == boost::math::ccmath::sqrt(T(3)));
+    static_assert(boost::math::ccmath::hypot(T(2), T(2), T(1)) == T(3));
+    static_assert(boost::math::ccmath::hypot(T(2), T(-2), T(1)) == T(3));
+    static_assert(boost::math::ccmath::abs(boost::math::ccmath::hypot(T(1), T(2), T(3)) - boost::math::ccmath::sqrt(T(14))) < tol);
+}
+
 int main()
 {
     test<float>();
@@ -67,6 +107,17 @@ int main()
     test<boost::multiprecision::float128>();
     #endif
 
+    test_3_arg<float>();
+    test_3_arg<double>();
+
+    #ifndef BOOST_MATH_NO_LONG_DOUBLE_MATH_FUNCTIONS
+    test_3_arg<long double>();
+    #endif
+    
+    #ifdef BOOST_HAS_FLOAT128
+    test_3_arg<boost::multiprecision::float128>();
+    #endif
+
     return 0;
 }
 #else

From b298d71bfa8923a43d80938b69dc4ddd3682d55e Mon Sep 17 00:00:00 2001
From: Matt Borland <matt@mattborland.com>
Date: Tue, 10 Jan 2023 14:51:55 -0800
Subject: [PATCH 2/2] Remove float128 testing

---
 test/ccmath_hypot_test.cpp | 4 ----
 1 file changed, 4 deletions(-)

diff --git a/test/ccmath_hypot_test.cpp b/test/ccmath_hypot_test.cpp
index c4cbc32c5d..9015ed32a2 100644
--- a/test/ccmath_hypot_test.cpp
+++ b/test/ccmath_hypot_test.cpp
@@ -113,10 +113,6 @@ int main()
     #ifndef BOOST_MATH_NO_LONG_DOUBLE_MATH_FUNCTIONS
     test_3_arg<long double>();
     #endif
-    
-    #ifdef BOOST_HAS_FLOAT128
-    test_3_arg<boost::multiprecision::float128>();
-    #endif
 
     return 0;
 }