Fix erroneous cast to unrepresentable values

include/boost/decimal/detail/to_integral.hpp

@@ -38,6 +38,7 @@ BOOST_DECIMAL_CUDA_CONSTEXPR auto to_integral(Decimal val) noexcept
 
     constexpr Decimal max_target_type { (std::numeric_limits<TargetType>::max)() };
     constexpr Decimal min_target_type { (std::numeric_limits<TargetType>::min)() };
+    constexpr Decimal one {1};
 
     if (isnan(val))
     {
@@ -49,6 +50,13 @@ BOOST_DECIMAL_CUDA_CONSTEXPR auto to_integral(Decimal val) noexcept
         }
         return static_cast<TargetType>(std::numeric_limits<TargetType>::max());
     }
+
+    // Anything in [0, 1) should be flushed to 0
+    if (abs(val) < one)
+    {
+        return static_cast<TargetType>(0);
+    }
+
     if (val > max_target_type || val < min_target_type)
     {
         #if defined(__clang__) && __clang_major__ >= 20
@@ -98,6 +106,7 @@ constexpr auto to_integral_128(Decimal val) noexcept
 {
     constexpr Decimal max_target_type { (std::numeric_limits<TargetType>::max)() };
     constexpr Decimal min_target_type { (std::numeric_limits<TargetType>::min)() };
+    constexpr Decimal one {1};
 
     if (isnan(val))
     {
@@ -110,6 +119,13 @@ constexpr auto to_integral_128(Decimal val) noexcept
 
         return static_cast<TargetType>(std::numeric_limits<TargetType>::max());
     }
+
+    // Anything in [0, 1) should be flushed to 0
+    if (abs(val) < one)
+    {
+        return static_cast<TargetType>(0);
+    }
+
     if (val > max_target_type || val < min_target_type)
     {
         #if defined(__clang__) && __clang_major__ >= 20

test/Jamfile

@@ -91,6 +91,7 @@ run github_issue_1306.cpp ;
 run github_issue_1312.cpp ;
 run github_issue_1319.cpp ;
 run github_issue_1329.cpp ;
+run github_issue_1361.cpp ;
 
 run link_1.cpp link_2.cpp link_3.cpp ;
 run quick.cpp ;

test/github_issue_1361.cpp

@@ -0,0 +1,55 @@
+// Copyright 2026 Matt Borland
+// Distributed under the Boost Software License, Version 1.0.
+// https://www.boost.org/LICENSE_1_0.txt
+//
+// See: https://github.com/boostorg/decimal/issues/1319
+
+#include <boost/decimal.hpp>
+#include <boost/core/lightweight_test.hpp>
+#include <limits>
+
+using namespace boost::decimal;
+
+#if !(defined(__clang__) && __clang_major__ < 9)
+
+template <typename T>
+void test()
+{
+    constexpr T zero {0};
+    constexpr T numerator {1, -20};
+    constexpr T res {"3.1830988618379067153776752674502872406891929148091289749533e-21"}; // Wolfram
+    const auto val {numerator / numbers::pi_v<T>};
+    BOOST_TEST_NE(zero, val);
+    BOOST_TEST_EQ(val, res);
+    const auto res_as_unsigned {static_cast<unsigned>(res)};
+    BOOST_TEST_EQ(0U, res_as_unsigned);
+    BOOST_TEST_EQ(0U, static_cast<unsigned>(val));
+
+    constexpr T small_angle {1, -4};
+    const T sin_small_angle {sin(small_angle)};
+    // Approx: 0.00009999999983333334
+    BOOST_TEST_GE(small_angle, sin_small_angle);
+    BOOST_TEST_LE(small_angle / 10U, sin_small_angle);
+
+    constexpr T smaller_angle {1, -20};
+    BOOST_TEST_EQ(smaller_angle, sin(smaller_angle));
+}
+
+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();
+}
+
+#else
+
+int main() { return 0; }
+
+#endif