Implement, test, and document trunc (#695)

doc/sf/ccmath.qbk

@@ -103,6 +103,12 @@ All of the following functions require C++17 or greater.
         template <typename Integer>
         inline constexpr double ceil(Integer arg) noexcept
 
+        template <typename Real>
+        inline constexpr Real trunc(Real arg) noexcept
+
+        template <typename Integer>
+        inline constexpr double trunc(Integer arg) noexcept
+
     } // Namespaces
 
 [endsect] [/section:ccmath Constexpr CMath]

include/boost/math/ccmath/ccmath.hpp

@@ -23,5 +23,6 @@
 #include <boost/math/ccmath/scalbln.hpp>
 #include <boost/math/ccmath/floor.hpp>
 #include <boost/math/ccmath/ceil.hpp>
+#include <boost/math/ccmath/trunc.hpp>
 
 #endif // BOOST_MATH_CCMATH_HPP

include/boost/math/ccmath/trunc.hpp

@@ -0,0 +1,67 @@
+//  (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_TRUNC_HPP
+#define BOOST_MATH_CCMATH_TRUNC_HPP
+
+#include <cmath>
+#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/floor.hpp>
+#include <boost/math/ccmath/ceil.hpp>
+
+namespace boost::math::ccmath {
+
+namespace detail {
+
+template <typename T>
+inline constexpr T trunc_impl(T arg) noexcept
+{
+    return (arg > 0) ? boost::math::ccmath::floor(arg) : boost::math::ccmath::ceil(arg);
+}
+
+} // Namespace detail
+
+template <typename Real, std::enable_if_t<!std::is_integral_v<Real>, bool> = true>
+inline constexpr Real trunc(Real arg) noexcept
+{
+    if(BOOST_MATH_IS_CONSTANT_EVALUATED(arg))
+    {
+        return boost::math::ccmath::abs(arg) == Real(0) ? arg :
+               boost::math::ccmath::isinf(arg) ? arg :
+               boost::math::ccmath::isnan(arg) ? arg :
+               boost::math::ccmath::detail::trunc_impl(arg);
+    }
+    else
+    {
+        using std::trunc;
+        return trunc(arg);
+    }
+}
+
+template <typename Z, std::enable_if_t<std::is_integral_v<Z>, bool> = true>
+inline constexpr double trunc(Z arg) noexcept
+{
+    return boost::math::ccmath::trunc(static_cast<double>(arg));
+}
+
+inline constexpr float truncf(float arg) noexcept
+{
+    return boost::math::ccmath::trunc(arg);
+}
+
+#ifndef BOOST_MATH_NO_LONG_DOUBLE_MATH_FUNCTIONS
+inline constexpr long double truncl(long double arg) noexcept
+{
+    return boost::math::ccmath::trunc(arg);
+}
+#endif
+
+} // Namespaces
+
+#endif // BOOST_MATH_CCMATH_TRUNC_HPP

test/Jamfile.v2

@@ -137,6 +137,7 @@ test-suite special_fun :
    [ run ccmath_scalbln_test.cpp ../../test/build//boost_unit_test_framework : : : [ requires cxx17_if_constexpr ] ]
    [ run ccmath_floor_test.cpp ../../test/build//boost_unit_test_framework : : : [ requires cxx17_if_constexpr ] ]
    [ run ccmath_ceil_test.cpp ../../test/build//boost_unit_test_framework : : : [ requires cxx17_if_constexpr ] ]
+   [ run ccmath_trunc_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_trunc_test.cpp

@@ -0,0 +1,63 @@
+//  (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/trunc.hpp>
+#include <boost/math/ccmath/isnan.hpp>
+#include <boost/math/ccmath/isinf.hpp>
+
+#ifdef BOOST_HAS_FLOAT128
+#include <boost/multiprecision/float128.hpp>
+#endif
+
+template <typename T>
+constexpr void test()
+{
+    if constexpr (std::numeric_limits<T>::has_quiet_NaN)
+    {
+        static_assert(boost::math::ccmath::isnan(boost::math::ccmath::trunc(std::numeric_limits<T>::quiet_NaN())), "If x is NaN, NaN is returned");
+    }
+
+    static_assert(!boost::math::ccmath::trunc(T(0)), "If x is +- 0, it is returned, unmodified");
+    static_assert(!boost::math::ccmath::trunc(T(-0)), "If x is +- 0, it is returned, unmodified");
+    
+    static_assert(boost::math::ccmath::isinf(boost::math::ccmath::trunc(std::numeric_limits<T>::infinity())), 
+                  "If x is +- inf, it is returned, unmodified");
+    static_assert(boost::math::ccmath::isinf(boost::math::ccmath::trunc(-std::numeric_limits<T>::infinity())), 
+                  "If x is +- inf, it is returned, unmodified");
+
+    static_assert(boost::math::ccmath::trunc(T(2)) == T(2));
+    static_assert(boost::math::ccmath::trunc(T(2.4)) == T(2));
+    static_assert(boost::math::ccmath::trunc(T(2.9)) == T(2));
+    static_assert(boost::math::ccmath::trunc(T(-2.7)) == T(-2));
+    static_assert(boost::math::ccmath::trunc(T(-2)) == T(-2));
+}
+
+#if !defined(BOOST_MATH_NO_CONSTEXPR_DETECTION) && !defined(BOOST_MATH_USING_BUILTIN_CONSTANT_P)
+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

test/compile_test/ccmath_trunc_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/trunc.hpp>
+#include "test_compile_result.hpp"
+
+void compile_and_link_test()
+{
+   check_result<float>(boost::math::ccmath::trunc(1.0f));
+   check_result<double>(boost::math::ccmath::trunc(1.0));
+#ifndef BOOST_MATH_NO_LONG_DOUBLE_MATH_FUNCTIONS
+   check_result<long double>(boost::math::ccmath::trunc(1.0l));
+#endif
+}