Add reproducer test set

Author: mborland

test/Jamfile

@@ -76,6 +76,7 @@ run github_issue_1107.cpp ;
 run github_issue_1110.cpp ;
 run github_issue_1112.cpp ;
 run github_issue_1174.cpp ;
+run github_issue_1260.cpp ;
 
 run link_1.cpp link_2.cpp link_3.cpp ;
 run quick.cpp ;

test/github_issue_1260.cpp

@@ -0,0 +1,27 @@
+// 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/1260
+
+#include <boost/decimal.hpp>
+#include <boost/core/lightweight_test.hpp>
+
+template <typename T>
+void test()
+{
+    const T lhs {"1E34"};
+    const T rhs {"-0.51"};
+    const T res {"9999999999999999999999999999999999"};
+
+    const T add_val {lhs + rhs};
+    BOOST_TEST_EQ(add_val, res);
+}
+
+int main()
+{
+    test<boost::decimal::decimal128_t>();
+    test<boost::decimal::decimal_fast128_t>();
+
+    return boost::report_errors();
+}