Merge pull request #343 from cppalliance/nan

Add cmath nan function

Author: mborland

include/boost/decimal/cmath.hpp

@@ -52,6 +52,7 @@
 #include <boost/decimal/detail/cmath/tanh.hpp>
 #include <boost/decimal/detail/cmath/tgamma.hpp>
 #include <boost/decimal/detail/cmath/trunc.hpp>
+#include <boost/decimal/detail/cmath/nan.hpp>
 #include <boost/decimal/numbers.hpp>
 
 // Macros from 3.6.2

include/boost/decimal/detail/cmath/nan.hpp

@@ -0,0 +1,57 @@
+// Copyright 2023 Matt Borland
+// Distributed under the Boost Software License, Version 1.0.
+// https://www.boost.org/LICENSE_1_0.txt
+
+#ifndef BOOST_DECIMAL_DETAIL_CMATH_NAN_HPP
+#define BOOST_DECIMAL_DETAIL_CMATH_NAN_HPP
+
+#include <boost/decimal/fwd.hpp>
+#include <boost/decimal/detail/config.hpp>
+#include <boost/decimal/detail/type_traits.hpp>
+#include <boost/decimal/cstdlib.hpp>
+#include <limits>
+
+#if !defined(BOOST_DECIMAL_DISABLE_CLIB)
+
+namespace boost {
+namespace decimal {
+
+namespace detail {
+
+template <typename TargetDecimalType>
+constexpr auto nan_impl(const char* arg) noexcept -> TargetDecimalType
+{
+    char* endptr {};
+    const auto val {strtod_impl<TargetDecimalType>(arg, &endptr)};
+    return val & std::numeric_limits<TargetDecimalType>::quiet_NaN();
+}
+
+} //namespace detail
+
+constexpr auto nand32(const char* arg) noexcept -> decimal32
+{
+    return detail::nan_impl<decimal32>(arg);
+}
+
+template <typename Dec>
+constexpr auto nan(const char* arg) noexcept -> Dec
+{
+    return detail::nan_impl<Dec>(arg);
+}
+
+constexpr auto nand64(const char* arg) noexcept -> decimal64
+{
+    return detail::nan_impl<decimal64>(arg);
+}
+
+constexpr auto nand128(const char* arg) noexcept -> decimal128
+{
+    return detail::nan_impl<decimal128>(arg);
+}
+
+} //namespace decimal
+} //namespace boost
+
+#endif //#if !defined(BOOST_DECIMAL_DISABLE_CLIB)
+
+#endif //BOOST_DECIMAL_DETAIL_CMATH_NAN_HPP

test/test_cmath.cpp

@@ -1340,6 +1340,16 @@ void test_exp2()
     BOOST_TEST_EQ(exp2(-std::numeric_limits<T>::infinity()), T(0 * dist(rng)));
 }
 
+#if !defined(BOOST_DECIMAL_DISABLE_CLIB)
+template <typename T>
+void test_nan()
+{
+    BOOST_TEST(!isnan(nan<T>("1") & std::numeric_limits<T>::quiet_NaN()));
+    BOOST_TEST(!isnan(nan<T>("2") & std::numeric_limits<T>::quiet_NaN()));
+    BOOST_TEST(!isnan(nan<T>("-1") & std::numeric_limits<T>::quiet_NaN()));
+}
+#endif
+
 int main()
 {
     test_fmax<decimal32>();
@@ -1448,5 +1458,11 @@ int main()
     test_exp2<decimal32>();
     test_exp2<decimal64>();
 
+    #if !defined(BOOST_DECIMAL_DISABLE_CLIB)
+    test_nan<decimal32>();
+    test_nan<decimal64>();
+    test_nan<decimal128>();
+    #endif
+
     return boost::report_errors();
 }