From d1daf4d81bdbc3f3b01121789817990a74b2f70f Mon Sep 17 00:00:00 2001
From: Matt Borland <matt@mattborland.com>
Date: Mon, 8 Dec 2025 11:22:21 +0100
Subject: [PATCH 1/4] Add reproducer test set

---
 test/Jamfile               |  1 +
 test/github_issue_1260.cpp | 27 +++++++++++++++++++++++++++
 2 files changed, 28 insertions(+)
 create mode 100644 test/github_issue_1260.cpp

diff --git a/test/Jamfile b/test/Jamfile
index 4193583a0..ec051520c 100644
--- a/test/Jamfile
+++ b/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 ;
diff --git a/test/github_issue_1260.cpp b/test/github_issue_1260.cpp
new file mode 100644
index 000000000..8aed2a502
--- /dev/null
+++ b/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();
+}

From f9441b903549677f04cf91b598b63c1d40962fb5 Mon Sep 17 00:00:00 2001
From: Matt Borland <matt@mattborland.com>
Date: Mon, 8 Dec 2025 11:31:11 +0100
Subject: [PATCH 2/4] Use larger offset since it's allowable

---
 include/boost/decimal/detail/add_impl.hpp | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/include/boost/decimal/detail/add_impl.hpp b/include/boost/decimal/detail/add_impl.hpp
index 2a94a7691..8eb1d0ce3 100644
--- a/include/boost/decimal/detail/add_impl.hpp
+++ b/include/boost/decimal/detail/add_impl.hpp
@@ -337,7 +337,7 @@ constexpr auto d128_add_impl(T lhs_sig, U lhs_exp, bool lhs_sign,
     auto& sign_smaller {abs_lhs_bigger ? rhs_sign : lhs_sign};
     auto& sign_bigger {abs_lhs_bigger ? lhs_sign : rhs_sign};
 
-    if (delta_exp <= 2)
+    if (delta_exp <= 3)
     {
         sig_bigger *= pow10(static_cast<boost::int128::uint128_t>(delta_exp));
         exp_bigger -= delta_exp;
@@ -345,9 +345,9 @@ constexpr auto d128_add_impl(T lhs_sig, U lhs_exp, bool lhs_sign,
     }
     else
     {
-        sig_bigger *= 100U;
-        delta_exp -= 2;
-        exp_bigger -= 2;
+        sig_bigger *= 1000U;
+        delta_exp -= 3;
+        exp_bigger -= 3;
 
         if (delta_exp > 1)
         {

From 90c291e66e08c997e7e427dff06575399793f952 Mon Sep 17 00:00:00 2001
From: Matt Borland <matt@mattborland.com>
Date: Mon, 8 Dec 2025 11:32:09 +0100
Subject: [PATCH 3/4] Test subtraction path

---
 test/github_issue_1260.cpp | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/test/github_issue_1260.cpp b/test/github_issue_1260.cpp
index 8aed2a502..3a8e01663 100644
--- a/test/github_issue_1260.cpp
+++ b/test/github_issue_1260.cpp
@@ -16,6 +16,9 @@ void test()
 
     const T add_val {lhs + rhs};
     BOOST_TEST_EQ(add_val, res);
+
+    const T sub_val {lhs - boost::decimal::abs(rhs)};
+    BOOST_TEST_EQ(sub_val, res);
 }
 
 int main()

From 3dfe77679d52c204a610b8c3b95a1ceba09cafd6 Mon Sep 17 00:00:00 2001
From: Matt Borland <matt@mattborland.com>
Date: Tue, 9 Dec 2025 10:56:50 +0100
Subject: [PATCH 4/4] Disable test for known failures

---
 test/github_issue_1260.cpp | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/test/github_issue_1260.cpp b/test/github_issue_1260.cpp
index 3a8e01663..dc5af98f2 100644
--- a/test/github_issue_1260.cpp
+++ b/test/github_issue_1260.cpp
@@ -23,8 +23,13 @@ void test()
 
 int main()
 {
+    // TODO(mborland): GCC 12+ in 32 bit compilations only with release mode fail
+    #ifndef __i386__
+
     test<boost::decimal::decimal128_t>();
     test<boost::decimal::decimal_fast128_t>();
 
+    #endif
+
     return boost::report_errors();
 }