Pad: add pad mode SYMMETRIC (#3229)

* Pad: add pad mode SYMMETRIC

* Style.

* Disable UT on unsupported backends.

src/ngraph/op/pad.hpp

@@ -34,7 +34,7 @@ namespace ngraph
             /// \param arg_pad_value The node producing the scalar value to be inserted for padding.
             /// \param padding_below The padding-below widths.
             /// \param padding_above The padding-above widths.
-            /// \param pad_mode The padding mode: CONSTANT(default), EDGE or REFLECT.
+            /// \param pad_mode The padding mode: CONSTANT(default), EDGE, REFLECT or SYMMETRIC.
             Pad(const std::shared_ptr<Node>& arg,
                 const std::shared_ptr<Node>& arg_pad_value,
                 const CoordinateDiff& padding_below,

src/ngraph/runtime/cpu/cpu_emitter.cpp

@@ -3027,7 +3027,9 @@ namespace ngraph
                     case ngraph::op::PadMode::REFLECT:
                         pad_mode_string = "ngraph::op::PadMode::REFLECT";
                         break;
-                    case ngraph::op::PadMode::SYMMETRIC: throw ngraph_error("Unsupported PadMode");
+                    case ngraph::op::PadMode::SYMMETRIC:
+                        pad_mode_string = "ngraph::op::PadMode::SYMMETRIC";
+                        break;
                     }
                     writer << "reference::pad<" << out[0].get_type() << ">(" << args[0].get_name()
                            << ",\n";

src/ngraph/runtime/gpu/unit_test.manifest

@@ -123,6 +123,7 @@ pad_reflect_1d_bottom_neg_bigger_than_tensor
 pad_reflect_1d_multi_reflect
 pad_reflect_2d
 pad_reflect_2d_with_neg
+pad_symmetric
 
 # Quantized operators are not supported on gpu backend
 model_dequantize_linear

src/ngraph/runtime/intelgpu/unit_test.manifest

@@ -40,6 +40,7 @@ pad_reflect_1d_bottom_neg_bigger_than_tensor
 pad_reflect_1d_multi_reflect
 pad_reflect_2d
 pad_reflect_2d_with_neg
+pad_symmetric
 
 # Not implemented
 batch_mat_mul_forward

src/ngraph/runtime/plaidml/unit_test.manifest

@@ -137,6 +137,7 @@ pad_reflect_2d_with_neg
 pad_negative_exterior_2d
 pad_negative_exterior_2d_all_negative
 pad_negative_exterior_4d
+pad_symmetric
 max_trivial_int8
 max_trivial_5d_int32
 max_3d_to_scalar_double

src/ngraph/runtime/reference/pad.hpp

@@ -164,8 +164,31 @@ namespace ngraph
                     }
                     case op::PadMode::SYMMETRIC:
                     {
-                        // TODO: Add support for Symmetric mode
-                        throw ngraph_error("Symmetric mode padding not supported");
+                        Coordinate c = in_coord; // have to copy because in_coord is const
+                        for (size_t i = 0; i < c.size(); i++)
+                        {
+                            ptrdiff_t pos = padding_below[i] - (c[i] + 1);
+                            if (pos >= 0)
+                            {
+                                c[i] = static_cast<size_t>(pos + padding_below[i]);
+                            }
+                            else
+                            {
+                                pos = -(pos + 1);
+                                ptrdiff_t src_dim = static_cast<ptrdiff_t>(arg0_shape[i]);
+                                if (pos < src_dim)
+                                {
+                                    c[i] = static_cast<size_t>(pos + padding_below[i]);
+                                }
+                                else
+                                {
+                                    c[i] = static_cast<size_t>(padding_below[i] + src_dim +
+                                                               padding_above[i] - pos);
+                                }
+                            }
+                        }
+                        v = arg0[input_transform.index(c)];
+                        break;
                     }
                     }
 

test/backend/pad.in.cpp

@@ -939,3 +939,36 @@ NGRAPH_TEST(${BACKEND_NAME}, pad_2channel_2image_asym)
                                   read_vector<float>(result),
                                   MIN_FLOAT_TOLERANCE_BITS));
 }
+
+NGRAPH_TEST(${BACKEND_NAME}, pad_symmetric)
+{
+    Shape shape_a{2, 3};
+    auto A = make_shared<op::Parameter>(element::f32, shape_a);
+    Shape shape_b{};
+    auto B = make_shared<op::Parameter>(element::f32, shape_b);
+    Shape shape_r{4, 7};
+    CoordinateDiff padding_below{1, 2};
+    CoordinateDiff padding_above{1, 2};
+    auto f = make_shared<Function>(
+        make_shared<op::Pad>(A, B, padding_below, padding_above, op::PadMode::SYMMETRIC),
+        ParameterVector{A, B});
+
+    auto backend = runtime::Backend::create("${BACKEND_NAME}");
+
+    // Create some tensors for input/output
+    auto a = backend->create_tensor(element::f32, shape_a);
+    copy_data(a, test::NDArray<float, 2>({{1, 2, 3}, {4, 5, 6}}).get_vector());
+    auto b = backend->create_tensor(element::f32, shape_b);
+    copy_data(b, vector<float>{2112});
+    auto result = backend->create_tensor(element::f32, shape_r);
+
+    auto handle = backend->compile(f);
+    handle->call_with_validate({result}, {a, b});
+    EXPECT_TRUE(test::all_close_f((test::NDArray<float, 2>({{2, 1, 1, 2, 3, 3, 2},
+                                                            {2, 1, 1, 2, 3, 3, 2},
+                                                            {5, 4, 4, 5, 6, 6, 5},
+                                                            {5, 4, 4, 5, 6, 6, 5}})
+                                       .get_vector()),
+                                  read_vector<float>(result),
+                                  MIN_FLOAT_TOLERANCE_BITS));
+}