Add signbit function
diff --git a/test/array_cwise.cpp b/test/array_cwise.cpp
index a7e0ff4..94c9451 100644
--- a/test/array_cwise.cpp
+++ b/test/array_cwise.cpp
@@ -219,7 +219,7 @@
   for (Exponent exponent = min_exponent; exponent < max_exponent; ++exponent) {
     test_exponent<Base, Exponent>(exponent);
   }
-};
+}
 
 void mixed_pow_test() {
   // The following cases will test promoting a smaller exponent type
@@ -260,6 +260,81 @@
   unary_pow_test<long long, int>();
 }
 
+namespace Eigen {
+namespace internal {
+template <typename Scalar>
+struct test_signbit_op {
+  Scalar constexpr operator()(const Scalar& a) const { return numext::signbit(a); }
+  template <typename Packet>
+  inline Packet packetOp(const Packet& a) const {
+    return psignbit(a);
+  }
+};
+template <typename Scalar>
+struct functor_traits<test_signbit_op<Scalar>> {
+  enum { Cost = 1, PacketAccess = true }; //todo: define HasSignbit flag
+};
+}  // namespace internal
+}  // namespace Eigen
+
+template <typename T, bool IsInteger = NumTraits<T>::IsInteger>
+struct ref_signbit_func_impl {
+    static bool run(const T& x) { return std::signbit(x); }
+};
+template <typename T>
+struct ref_signbit_func_impl<T, true> {
+    // MSVC (perhaps others) does not have a std::signbit overload for integers
+    static bool run(const T& x) { return x < T(0); }
+};
+template <typename T>
+bool ref_signbit_func(const T& x) {
+    return ref_signbit_func_impl<T>::run(x);
+}
+
+template <typename Scalar>
+void signbit_test() {
+  Scalar true_mask;
+  std::memset(static_cast<void*>(&true_mask), 0xff, sizeof(Scalar));
+  Scalar false_mask;
+  std::memset(static_cast<void*>(&false_mask), 0x00, sizeof(Scalar));
+
+  const size_t size = 100 * internal::packet_traits<Scalar>::size;
+  ArrayX<Scalar> x(size), y(size);
+  x.setRandom();
+  std::vector<Scalar> special_vals = special_values<Scalar>();
+  for (size_t i = 0; i < special_vals.size(); i++) {
+    x(2 * i + 0) = special_vals[i];
+    x(2 * i + 1) = -special_vals[i];
+  }
+  y = x.unaryExpr(internal::test_signbit_op<Scalar>());
+
+  bool all_pass = true;
+  for (size_t i = 0; i < size; i++) {
+    const Scalar ref_val = ref_signbit_func(x(i)) ? true_mask : false_mask;
+    bool not_same = internal::predux_any(internal::bitwise_helper<Scalar>::bitwise_xor(ref_val, y(i)));
+    if (not_same) std::cout << "signbit(" << x(i) << ") != " << y(i) << "\n";
+    all_pass = all_pass && !not_same;
+  }
+
+  VERIFY(all_pass);
+}
+void signbit_tests() {
+  signbit_test<float>();
+  signbit_test<double>();
+  signbit_test<Eigen::half>();
+  signbit_test<Eigen::bfloat16>();
+
+  signbit_test<uint8_t>();
+  signbit_test<uint16_t>();
+  signbit_test<uint32_t>();
+  signbit_test<uint64_t>();
+
+  signbit_test<int8_t>();
+  signbit_test<int16_t>();
+  signbit_test<int32_t>();
+  signbit_test<int64_t>();
+}
+
 template<typename ArrayType> void array(const ArrayType& m)
 {
   typedef typename ArrayType::Scalar Scalar;
@@ -855,6 +930,35 @@
   VERIFY( (m2 == m1.unaryExpr(arithmetic_shift_right<9>())).all() );
 }
 
+template <typename ArrayType>
+struct signed_shift_test_impl {
+  typedef typename ArrayType::Scalar Scalar;
+  static constexpr size_t Size = sizeof(Scalar);
+  static constexpr size_t MaxShift = (CHAR_BIT * Size) - 1;
+
+  template <size_t N = 0>
+  static inline std::enable_if_t<(N >  MaxShift), void> run(const ArrayType&  ) {}
+  template <size_t N = 0>
+  static inline std::enable_if_t<(N <= MaxShift), void> run(const ArrayType& m) {
+    const Index rows = m.rows();
+    const Index cols = m.cols();
+
+    ArrayType m1 = ArrayType::Random(rows, cols), m2(rows, cols);
+
+    m2 = m1.unaryExpr([](const Scalar& x) { return x >> N; });
+    VERIFY((m2 == m1.unaryExpr(internal::scalar_shift_right_op<Scalar, N>())).all());
+
+    m2 = m1.unaryExpr([](const Scalar& x) { return x << N; });
+    VERIFY((m2 == m1.unaryExpr( internal::scalar_shift_left_op<Scalar, N>())).all());
+
+    run<N + 1>(m);
+  }
+};
+template <typename ArrayType>
+void signed_shift_test(const ArrayType& m) {
+    signed_shift_test_impl<ArrayType>::run(m);
+}
+
 EIGEN_DECLARE_TEST(array_cwise)
 {
   for(int i = 0; i < g_repeat; i++) {
@@ -867,6 +971,9 @@
     CALL_SUBTEST_6( array(Array<Index,Dynamic,Dynamic>(internal::random<int>(1,EIGEN_TEST_MAX_SIZE), internal::random<int>(1,EIGEN_TEST_MAX_SIZE))) );
     CALL_SUBTEST_6( array_integer(ArrayXXi(internal::random<int>(1,EIGEN_TEST_MAX_SIZE), internal::random<int>(1,EIGEN_TEST_MAX_SIZE))) );
     CALL_SUBTEST_6( array_integer(Array<Index,Dynamic,Dynamic>(internal::random<int>(1,EIGEN_TEST_MAX_SIZE), internal::random<int>(1,EIGEN_TEST_MAX_SIZE))) );
+    CALL_SUBTEST_7( signed_shift_test(ArrayXXi(internal::random<int>(1, EIGEN_TEST_MAX_SIZE), internal::random<int>(1, EIGEN_TEST_MAX_SIZE))));
+    CALL_SUBTEST_7( signed_shift_test(Array<Index, Dynamic, Dynamic>(internal::random<int>(1, EIGEN_TEST_MAX_SIZE), internal::random<int>(1, EIGEN_TEST_MAX_SIZE))));
+
   }
   for(int i = 0; i < g_repeat; i++) {
     CALL_SUBTEST_1( comparisons(Array<float, 1, 1>()) );
@@ -897,6 +1004,7 @@
   for(int i = 0; i < g_repeat; i++) {
     CALL_SUBTEST_6( int_pow_test() );
     CALL_SUBTEST_7( mixed_pow_test() );
+    CALL_SUBTEST_8( signbit_tests() );
   }
 
   VERIFY((internal::is_same< internal::global_math_functions_filtering_base<int>::type, int >::value));