constexpr remainder (#700)

boostorg · Oct 6, 2021 · 8e8f6ec · 8e8f6ec
1 parent 6d5aeb0
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diff --git a/doc/sf/ccmath.qbk b/doc/sf/ccmath.qbk
@@ -131,6 +131,12 @@ All of the following functions require C++17 or greater.
         inline constexpr Promoted fmod(Arithmetic1 x, Arithmetic2 y) noexcept
         The Promoted return type will have at least double prescision, but be up to the highest precision argument.
 
+        template <typename Real>
+        inline constexpr Real remainder(Real x, Real y) noexcept
+
+        template <typename Arithmetic1, typename Arithmetic2>
+        inline constexpr Promoted remainder(Arithmetic1 x, Arithmetic2 y) noexcept
+
     } // Namespaces
 
 [endsect] [/section:ccmath Constexpr CMath]
diff --git a/include/boost/math/ccmath/ccmath.hpp b/include/boost/math/ccmath/ccmath.hpp
@@ -27,5 +27,6 @@
 #include <boost/math/ccmath/modf.hpp>
 #include <boost/math/ccmath/round.hpp>
 #include <boost/math/ccmath/fmod.hpp>
+#include <boost/math/ccmath/remainder.hpp>
 
 #endif // BOOST_MATH_CCMATH_HPP
diff --git a/include/boost/math/ccmath/remainder.hpp b/include/boost/math/ccmath/remainder.hpp
@@ -0,0 +1,107 @@
+//  (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_REMAINDER_HPP
+#define BOOST_MATH_CCMATH_REMAINDER_HPP
+
+#include <cmath>
+#include <cstdint>
+#include <limits>
+#include <type_traits>
+#include <boost/math/tools/is_constant_evaluated.hpp>
+#include <boost/math/ccmath/abs.hpp>
+#include <boost/math/ccmath/isinf.hpp>
+#include <boost/math/ccmath/isnan.hpp>
+#include <boost/math/ccmath/isfinite.hpp>
+#include <boost/math/ccmath/modf.hpp>
+
+namespace boost::math::ccmath {
+
+namespace detail {
+
+template <typename T>
+inline constexpr T remainder_impl(const T x, const T y) noexcept
+{
+    T n = 0;
+    const T fractional_part = boost::math::ccmath::modf((x / y), &n);
+
+    if(fractional_part > T(1.0/2))
+    {
+        ++n;
+    }
+    else if(fractional_part < T(-1.0/2))
+    {
+        --n;
+    }
+
+    return x - n*y;
+}
+
+} // Namespace detail
+
+template <typename Real, std::enable_if_t<!std::is_integral_v<Real>, bool> = true>
+inline constexpr Real remainder(Real x, Real y) noexcept
+{
+    if(BOOST_MATH_IS_CONSTANT_EVALUATED(x))
+    {
+        return boost::math::ccmath::isinf(x) && !boost::math::ccmath::isnan(y) ? std::numeric_limits<Real>::quiet_NaN() :
+               boost::math::ccmath::abs(y) == Real(0) && !boost::math::ccmath::isnan(x) ? std::numeric_limits<Real>::quiet_NaN() :
+               boost::math::ccmath::isnan(x) || boost::math::ccmath::isnan(y) ? std::numeric_limits<Real>::quiet_NaN() :
+               boost::math::ccmath::detail::remainder_impl<Real>(x, y);
+    }
+    else
+    {
+        using std::remainder;
+        return remainder(x, y);
+    }
+}
+
+template <typename T1, typename T2>
+inline constexpr auto remainder(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::remainder(promoted_type(x), promoted_type(y));
+    }
+    else
+    {
+        using std::remainder;
+        return remainder(x, y);
+    }
+}
+
+inline constexpr float remainderf(float x, float y) noexcept
+{
+    return boost::math::ccmath::remainder(x, y);
+}
+
+#ifndef BOOST_MATH_NO_LONG_DOUBLE_MATH_FUNCTIONS
+inline constexpr long double remainderl(long double x, long double y) noexcept
+{
+    return boost::math::ccmath::remainder(x, y);
+}
+#endif
+
+} // Namespaces
+
+#endif // BOOST_MATH_CCMATH_REMAINDER_HPP
diff --git a/test/Jamfile.v2 b/test/Jamfile.v2
@@ -141,6 +141,7 @@ test-suite special_fun :
    [ run ccmath_modf_test.cpp ../../test/build//boost_unit_test_framework : : : [ requires cxx17_if_constexpr ] ]
    [ run ccmath_round_test.cpp ../../test/build//boost_unit_test_framework : : : [ requires cxx17_if_constexpr ] ]
    [ 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 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  ]

diff --git a/test/ccmath_remainder_test.cpp b/test/ccmath_remainder_test.cpp
@@ -0,0 +1,85 @@
+//  (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/remainder.hpp>
+#include <boost/math/ccmath/isnan.hpp>
+#include <boost/math/ccmath/isinf.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::remainder(std::numeric_limits<T>::quiet_NaN(), T(1))), "If x is NaN, NaN is returned");
+        static_assert(boost::math::ccmath::isnan(boost::math::ccmath::remainder(T(1), std::numeric_limits<T>::quiet_NaN())), "If y is NaN, NaN is returned");
+    }
+
+    static_assert(boost::math::ccmath::isnan(boost::math::ccmath::remainder(std::numeric_limits<T>::infinity(), T(1))));
+    static_assert(boost::math::ccmath::isnan(boost::math::ccmath::remainder(-std::numeric_limits<T>::infinity(), T(1))));
+    static_assert(boost::math::ccmath::isnan(boost::math::ccmath::remainder(T(1), T(0))));
+    static_assert(boost::math::ccmath::isnan(boost::math::ccmath::remainder(T(1), T(-0))));
+
+    // Functionality
+    static_assert(boost::math::ccmath::remainder(T(6), T(2)) == T(0));
+    static_assert(boost::math::ccmath::remainder(T(3.0/2), T(1.0) == T(3.0/2)));
+    static_assert(boost::math::ccmath::remainder(T(7.0/3), T(2.0) == T(1.0/3)));
+    static_assert(boost::math::ccmath::remainder(T(-8.0/3), T(2.0) == T(-2.0/3)));
+    static_assert(boost::math::ccmath::remainder(T(-0), T(1)) == T(-0));
+
+    // Not exact values but pulled from https://en.cppreference.com/w/cpp/numeric/math/remainder as general functionality tests so allow for some error
+    // std::is_floating_point_v excludes multi-precision types
+    if constexpr (std::is_floating_point_v<T>)
+    {
+        static_assert(boost::math::ccmath::abs(boost::math::ccmath::remainder(T(5.1l), T(3.0l)) - T(-0.9l)) < 2*std::numeric_limits<T>::epsilon());
+        static_assert(boost::math::ccmath::abs(boost::math::ccmath::remainder(T(-5.1l), T(3.0l)) - T(0.9l)) < 2*std::numeric_limits<T>::epsilon());
+        static_assert(boost::math::ccmath::abs(boost::math::ccmath::remainder(T(5.1l), T(-3.0l)) - T(-0.9l)) < 2*std::numeric_limits<T>::epsilon());
+        static_assert(boost::math::ccmath::abs(boost::math::ccmath::remainder(T(-5.1l), T(-3.0l)) - T(0.9l)) < 2*std::numeric_limits<T>::epsilon());
+    }
+
+    // Correct promoted types
+    if constexpr (!std::is_same_v<T, float>)
+    {
+        constexpr auto test_type = boost::math::ccmath::remainder(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::remainder(1.0f, 1);
+        static_assert(std::is_same_v<double, std::remove_cv_t<decltype(test_type)>>);
+    }
+}
+
+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
diff --git a/test/compile_test/ccmath_remainder_incl_test.cpp b/test/compile_test/ccmath_remainder_incl_test.cpp
@@ -0,0 +1,16 @@
+//  (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 <boost/math/ccmath/remainder.hpp>
+#include "test_compile_result.hpp"
+
+void compile_and_link_test()
+{
+   check_result<float>(boost::math::ccmath::remainder(1.0f, 1.0f));
+   check_result<double>(boost::math::ccmath::remainder(1.0, 1.0));
+#ifndef BOOST_MATH_NO_LONG_DOUBLE_MATH_FUNCTIONS
+   check_result<long double>(boost::math::ccmath::remainder(1.0l, 1.0l));
+#endif
+}