Fix construction from negative infinity binary floats

include/boost/decimal/decimal128_t.hpp

@@ -1052,10 +1052,14 @@ BOOST_DECIMAL_CXX20_CONSTEXPR decimal128_t::decimal128_t(const Float val) noexce
     {
         *this = from_bits(detail::d128_nan_mask);
     }
-    else if (val == std::numeric_limits<Float>::infinity() || val == -std::numeric_limits<Float>::infinity())
+    else if (val == std::numeric_limits<Float>::infinity())
     {
         *this = from_bits(detail::d128_inf_mask);
     }
+    else if (val == -std::numeric_limits<Float>::infinity())
+    {
+        *this = -from_bits(detail::d128_inf_mask);
+    }
     else
     #endif
     {

include/boost/decimal/decimal32_t.hpp

@@ -1801,10 +1801,14 @@ BOOST_DECIMAL_CXX20_CONSTEXPR decimal32_t::decimal32_t(const Float val) noexcept
     {
         *this = boost::decimal::from_bits(boost::decimal::detail::d32_nan_mask);
     }
-    else if (val == std::numeric_limits<Float>::infinity() || val == -std::numeric_limits<Float>::infinity())
+    else if (val == std::numeric_limits<Float>::infinity())
     {
         *this = boost::decimal::from_bits(boost::decimal::detail::d32_inf_mask);
     }
+    else if (val == -std::numeric_limits<Float>::infinity())
+    {
+        *this = -boost::decimal::from_bits(boost::decimal::detail::d32_inf_mask);
+    }
     else
     #endif
     {

include/boost/decimal/decimal64_t.hpp

@@ -1006,10 +1006,14 @@ BOOST_DECIMAL_CXX20_CONSTEXPR decimal64_t::decimal64_t(const Float val) noexcept
     {
         *this = from_bits(detail::d64_nan_mask);
     }
-    else if (val == std::numeric_limits<Float>::infinity() || val == -std::numeric_limits<Float>::infinity())
+    else if (val == std::numeric_limits<Float>::infinity())
     {
         *this = from_bits(detail::d64_inf_mask);
     }
+    else if (val == -std::numeric_limits<Float>::infinity())
+    {
+        *this = -from_bits(detail::d64_inf_mask);
+    }
     else
     #endif
     {

include/boost/decimal/decimal_fast128_t.hpp

@@ -619,10 +619,15 @@ BOOST_DECIMAL_CXX20_CONSTEXPR decimal_fast128_t::decimal_fast128_t(const Float v
     {
         significand_ = detail::d128_fast_qnan;
     }
-    else if (val == std::numeric_limits<Float>::infinity() || val == -std::numeric_limits<Float>::infinity())
+    else if (val == std::numeric_limits<Float>::infinity())
     {
         significand_ = detail::d128_fast_inf;
     }
+    else if (val == -std::numeric_limits<Float>::infinity())
+    {
+        significand_ = detail::d128_fast_inf;
+        sign_ = true;
+    }
     else
     #endif
     {

include/boost/decimal/decimal_fast32_t.hpp

@@ -724,10 +724,15 @@ BOOST_DECIMAL_CXX20_CONSTEXPR decimal_fast32_t::decimal_fast32_t(const Float val
     {
         significand_ = detail::d32_fast_qnan;
     }
-    else if (val == std::numeric_limits<Float>::infinity() || val == -std::numeric_limits<Float>::infinity())
+    else if (val == std::numeric_limits<Float>::infinity())
     {
         significand_ = detail::d32_fast_inf;
     }
+    else if (val == -std::numeric_limits<Float>::infinity())
+    {
+        significand_ = detail::d32_fast_inf;
+        sign_ = true;
+    }
     else
     #endif
     {

include/boost/decimal/decimal_fast64_t.hpp

@@ -621,10 +621,15 @@ BOOST_DECIMAL_CXX20_CONSTEXPR decimal_fast64_t::decimal_fast64_t(const Float val
     {
         significand_ = detail::d64_fast_qnan;
     }
-    else if (val == std::numeric_limits<Float>::infinity() || val == -std::numeric_limits<Float>::infinity())
+    else if (val == std::numeric_limits<Float>::infinity())
     {
         significand_ = detail::d64_fast_inf;
     }
+    else if (val == -std::numeric_limits<Float>::infinity())
+    {
+        significand_ = detail::d64_fast_inf;
+        sign_ = true;
+    }
     else
     #endif
     {

test/Jamfile

@@ -96,6 +96,7 @@ run github_issue_1361.cpp ;
 run github_issue_1378.cpp ;
 run github_issue_1383.cpp ;
 run github_issue_1384.cpp ;
+run github_issue_1398.cpp ;
 
 run link_1.cpp link_2.cpp link_3.cpp ;
 run quick.cpp ;

test/github_issue_1384.cpp

@@ -1,3 +1,8 @@
+// Copyright 2026 Chris Kormanyos
+// Distributed under the Boost Software License, Version 1.0.
+// https://www.boost.org/LICENSE_1_0.txt
+//
+// See: https://github.com/boostorg/decimal/issues/1384
 
 #include <boost/core/lightweight_test.hpp>
 

test/github_issue_1398.cpp

@@ -0,0 +1,42 @@
+// Copyright 2026 Chris Kormanyos
+// Distributed under the Boost Software License, Version 1.0.
+// https://www.boost.org/LICENSE_1_0.txt
+//
+// See: https://github.com/boostorg/decimal/issues/1398
+
+#include <boost/decimal.hpp>
+#include <boost/core/lightweight_test.hpp>
+#include <limits>
+
+template <typename T, typename U>
+void test_driver()
+{
+    using namespace boost::decimal;
+
+    constexpr auto builtin_neg_inf = -std::numeric_limits<T>::infinity();
+
+    const auto val = U(builtin_neg_inf);
+    BOOST_TEST(isinf(val));
+    BOOST_TEST(val < 0);
+}
+
+template <typename T>
+void test()
+{
+    using namespace boost::decimal;
+
+    test_driver<T, decimal32_t>();
+    test_driver<T, decimal64_t>();
+    test_driver<T, decimal128_t>();
+    test_driver<T, decimal_fast32_t>();
+    test_driver<T, decimal_fast64_t>();
+    test_driver<T, decimal_fast128_t>();
+}
+
+int main()
+{
+    test<float>();
+    test<double>();
+
+    return boost::report_errors();
+}