Minimal implementation of ccmath

[CI SKIP]

.gitignore

@@ -20,3 +20,7 @@ Makefile
 **/CMakeFiles/**
 **CTestTestfile.cmake
 DartConfiguration.tcl
+
+# Modules
+*.gcm
+*.out

include/boost/math/ccmath/ccmath.cpp

@@ -0,0 +1,142 @@
+//  (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)
+//
+//  A module containing all of the constexpr implementation of <cmath>
+
+// Global module fragment required for non-module preprocessing
+module;
+
+#include <boost/math/tools/config.hpp>
+#include <boost/math/tools/is_constant_evaluated.hpp>
+#include <cmath>
+#include <cstdint>
+#include <cstdlib>
+#include <cinttypes>
+#include <type_traits>
+#include <limits>
+#include <stdexcept>
+
+export module boost_math_ccmath;
+
+// Forward Declarations
+export namespace boost::math::ccmath {
+
+template <typename T>
+inline constexpr bool isnan(T x);
+
+template <typename T>
+inline constexpr bool isinf(T x);
+
+template <typename T, std::enable_if_t<!std::is_unsigned_v<T>, bool> = true>
+inline constexpr T abs(T x) noexcept;
+
+template <typename T, std::enable_if_t<std::is_unsigned_v<T>, bool> = true>
+inline constexpr T abs(T x) noexcept;
+
+}
+
+namespace boost::math::ccmath::detail {
+
+template <typename T> 
+inline constexpr T abs_impl(T x) noexcept
+{
+    return boost::math::ccmath::isnan(x) ? std::numeric_limits<T>::quiet_NaN() : 
+           boost::math::ccmath::isinf(x) ? std::numeric_limits<T>::infinity() : 
+           x == -0 ? T(0) :
+           x == (std::numeric_limits<T>::min)() ? std::numeric_limits<T>::quiet_NaN() : 
+           x > 0 ? x : -x;
+}
+
+}
+
+// Useable Functions
+
+export namespace boost::math::ccmath {
+
+template <typename T>
+inline constexpr bool isnan(T x)
+{
+    if(BOOST_MATH_IS_CONSTANT_EVALUATED(x))
+    {
+        return x != x;
+    }
+    else
+    {
+        using std::isnan;
+
+        if constexpr (!std::is_integral_v<T>)
+        {
+            return isnan(x);
+        }
+        else
+        {
+            return isnan(static_cast<double>(x));
+        }
+    }
+}
+
+template <typename T>
+inline constexpr bool isinf(T x)
+{
+    if(BOOST_MATH_IS_CONSTANT_EVALUATED(x))
+    {
+        return x == std::numeric_limits<T>::infinity() || -x == std::numeric_limits<T>::infinity();
+    }
+    else
+    {
+        using std::isinf;
+
+        if constexpr (!std::is_integral_v<T>)
+        {
+            return isinf(x);
+        }
+        else
+        {
+            return isinf(static_cast<double>(x));
+        }
+    }
+}
+
+template <typename T, std::enable_if_t<!std::is_unsigned_v<T>, bool> = true>
+inline constexpr T abs(T x) noexcept
+{
+    if(BOOST_MATH_IS_CONSTANT_EVALUATED(x))
+    {
+        return detail::abs_impl<T>(x);
+    }
+    else
+    {
+        using std::abs;
+        return abs(x);
+    }
+}
+
+// If abs() is called with an argument of type X for which is_unsigned_v<X> is true and if X
+// cannot be converted to int by integral promotion (7.3.7), the program is ill-formed.
+template <typename T, std::enable_if_t<std::is_unsigned_v<T>, bool> = true>
+inline constexpr T abs(T x) noexcept
+{
+    if constexpr (std::is_convertible_v<T, int>)
+    {
+        return detail::abs_impl<int>(static_cast<int>(x));
+    }
+    else
+    {
+        static_assert(sizeof(T) == 0, "Taking the absolute value of an unsigned value not covertible to int is UB.");
+        return T(0); // Unreachable, but suppresses warnings
+    }
+}
+
+inline constexpr long int labs(long int j) noexcept
+{
+    return boost::math::ccmath::abs(j);
+}
+
+inline constexpr long long int llabs(long long int j) noexcept
+{
+    return boost::math::ccmath::abs(j);
+}
+
+}

test/ccmath_module_test.cpp

@@ -0,0 +1,12 @@
+//  (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)
+
+import boost_math_ccmath;
+
+int main()
+{
+    constexpr double test = boost::math::ccmath::abs(-2.0);
+    static_assert(test == 2.0);
+}