Merge pull request #1295 from cppalliance/1294

Fix conditional logic in `round` family

Author: mborland

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

@@ -43,11 +43,11 @@ constexpr auto round(const T num) noexcept
     T iptr {};
     const auto x {modf(num, &iptr)};
 
-    if (x >= half && iptr > 0)
+    if (x >= half)
     {
         ++iptr;
     }
-    else if (abs(x) >= half && iptr < 0)
+    else if (x <= -half)
     {
         --iptr;
     }

test/Jamfile

@@ -82,6 +82,7 @@ run github_issue_1110.cpp ;
 run github_issue_1112.cpp ;
 run github_issue_1174.cpp ;
 run github_issue_1260.cpp ;
+run github_issue_1294.cpp ;
 
 run link_1.cpp link_2.cpp link_3.cpp ;
 run quick.cpp ;

test/github_issue_1294.cpp

@@ -0,0 +1,59 @@
+// Copyright 2025 Matt Borland
+// Distributed under the Boost Software License, Version 1.0.
+// https://www.boost.org/LICENSE_1_0.txt
+//
+// See: https://github.com/cppalliance/decimal/issues/1294
+
+#include <boost/decimal.hpp>
+#include <boost/core/lightweight_test.hpp>
+
+using namespace boost::decimal;
+
+template <typename T>
+void test_round_down()
+{
+    const T val {"0.499"};
+    constexpr T ref_1 {1};
+    constexpr T ref_0 {0};
+
+    BOOST_TEST_EQ(ceil(val), ref_1);
+    BOOST_TEST_EQ(floor(val), ref_0);
+    BOOST_TEST_EQ(trunc(val), ref_0);
+    BOOST_TEST_EQ(round(val), ref_0);
+    BOOST_TEST_EQ(lround(val), 0L);
+    BOOST_TEST_EQ(nearbyint(val), 0);
+    BOOST_TEST_EQ(lrint(val), 0L);
+    BOOST_TEST_EQ(llrint(val), 0LL);
+}
+
+template <typename T>
+void test()
+{
+    const T val {"0.999"};
+    constexpr T ref_1 {1};
+    constexpr T ref_0 {0};
+
+    BOOST_TEST_EQ(ceil(val), ref_1);
+    BOOST_TEST_EQ(floor(val), ref_0);
+    BOOST_TEST_EQ(trunc(val), ref_0);
+    BOOST_TEST_EQ(round(val), ref_1);
+    BOOST_TEST_EQ(lround(val), 1L);
+    BOOST_TEST_EQ(nearbyint(val), 1);
+    BOOST_TEST_EQ(lrint(val), 1L);
+    BOOST_TEST_EQ(llrint(val), 1LL);
+
+    test_round_down<T>();
+}
+
+int main()
+{
+    test<decimal32_t>();
+    test<decimal64_t>();
+    test<decimal128_t>();
+
+    test<decimal_fast32_t>();
+    test<decimal_fast64_t>();
+    test<decimal_fast128_t>();
+
+    return boost::report_errors();
+}