[BUGFIX] Fix numpy pad operator

src/api/operator/numpy/np_pad_op.cc

@@ -51,20 +51,70 @@ inline int String2MXNetPadType(const std::string& s) {
   return 0;
 }
 
+inline Tuple<Tuple<int>> BroadcastPadWidth(int ndim, runtime::ADT adt) {
+  std::vector<mxnet::Tuple<int>> temp;
+  int adt_size = adt.size();
+  if (const runtime::IntegerObj* pad = adt[0].as<runtime::IntegerObj>()) {
+    if (adt_size == 1) {
+      int pad_width = static_cast<int>(pad->value);
+      if (ndim == 1) {
+        temp.emplace_back(mxnet::Tuple<int>({pad_width}));
+        temp.emplace_back(mxnet::Tuple<int>({pad_width}));
+      } else {
+        for (int dim = 0; dim < ndim; dim++) {
+          temp.emplace_back(mxnet::Tuple<int>({pad_width, pad_width}));
+        }
+      }
+    } else {
+      CHECK_EQ(adt_size, 2) << "Invalid Input pad_width";
+      int pad_before = static_cast<int>(pad->value);
+      int pad_after = static_cast<int>(Downcast<runtime::Integer, ObjectRef>(adt[1])->value);
+      if (ndim == 1) {
+        temp.emplace_back(mxnet::Tuple<int>({pad_before}));
+        temp.emplace_back(mxnet::Tuple<int>({pad_after}));
+      } else {
+        for (int dim = 0; dim < ndim; dim++) {
+          temp.emplace_back(mxnet::Tuple<int>({pad_before, pad_after}));
+        }
+      }
+    }
+  } else {
+    if (adt_size == 1) {
+      if (ndim == 1) {
+        runtime::ADT pad_adt = Downcast<runtime::ADT, ObjectRef>(adt[0]);
+        int pad_before =
+            static_cast<int>(Downcast<runtime::Integer, ObjectRef>(pad_adt[0])->value);
+        int pad_after =
+            static_cast<int>(Downcast<runtime::Integer, ObjectRef>(pad_adt[1])->value);
+        temp.emplace_back(mxnet::Tuple<int>({pad_before}));
+        temp.emplace_back(mxnet::Tuple<int>({pad_after}));
+      } else {
+        for (int dim = 0; dim < ndim; dim++) {
+          temp.emplace_back(mxnet::Tuple<int>(adt[0]));
+        }
+      }
+    } else {
+      CHECK_EQ(adt_size, ndim) << "Invalid Input pad_width";
+      for (int dim = 0; dim < ndim; dim++) {
+        temp.emplace_back(mxnet::Tuple<int>(adt[dim]));
+      }
+    }
+  }
+  return Tuple<Tuple<int>>(temp.begin(), temp.end());
+}
+
 MXNET_REGISTER_API("_npi.pad")
 .set_body([](runtime::MXNetArgs args, runtime::MXNetRetValue* ret) {
   using namespace runtime;
   const nnvm::Op* op = Op::Get("_npi_pad");
   nnvm::NodeAttrs attrs;
   op::NumpyPadParam param;
+  NDArray* inputs[] = {args[0].operator mxnet::NDArray*()};
+  mxnet::TShape ashape = inputs[0]->shape();
+  int ndim = ashape.ndim();
   ADT adt = Downcast<ADT, ObjectRef>(args[1].operator ObjectRef());
-  int ndim = adt.size();
-  std::vector<mxnet::Tuple<int>> temp;
-  int counter = 0;
-  for (counter = 0; counter < ndim; counter++) {
-    temp.emplace_back(mxnet::Tuple<int>(adt[counter]));
-  }
-  param.pad_width = Tuple<Tuple<int>>(temp.begin(), temp.end());
+  // broadcast pad_width to (ndim, 2)
+  param.pad_width = BroadcastPadWidth(ndim, adt);
   param.mode = String2MXNetPadType(args[2].operator std::string());
   if (args[3].type_code() != kNull) {
     param.constant_values = args[3].operator double();
@@ -77,7 +127,6 @@ MXNET_REGISTER_API("_npi.pad")
   SetAttrDict<op::NumpyPadParam>(&attrs);
   int num_inputs = 1;
   int num_outputs = 0;
-  NDArray* inputs[] = {args[0].operator mxnet::NDArray*()};
   auto ndoutputs = Invoke(op, &attrs, num_inputs, inputs, &num_outputs, nullptr);
   *ret = reinterpret_cast<mxnet::NDArray*>(ndoutputs[0]);
 });

tests/python/unittest/test_numpy_op.py

@@ -8325,7 +8325,7 @@ def __init__(self, pad_width, mode='constant'):
         def hybrid_forward(self,F,A,**kwargs):
             return F.np.pad(A, self._pad_width, mode=self._mode, **kwargs)
 
-    shapes = [(1,5), (2,2), (2,2), (3,3), (2,3), (3,4,5)]
+    shapes = [6, (1,5), (2,2), (2,2), (3,3), (2,3), (3,4,5)]
     dtypes = [np.int8, np.uint8, np.int32, np.int64, np.float16, np.float32, np.float64]
     mode = ['constant', 'reflect', 'symmetric', 'edge', 'minimum', 'maximum']
     for hybridize, shape, dtype, in itertools.product([False,True], shapes, dtypes):