Implement Round for lower opsets (#1589)

Signed-off-by: Tom Wildenhain <[email protected]>

Co-authored-by: Guenther Schmuelling <[email protected]>

Author: TomWildenhain-Microsoft

tests/test_backend.py

@@ -4349,6 +4349,14 @@ def func(x):
             return tf.identity(x_, name=_TFOUTPUT)
         self._run_test_case(func, [_OUTPUT], {_INPUT: x_val})
 
+    def test_round_approx(self):
+        # In lower opsets there is no Round, but we can approximate it forgoing nearest even
+        x_val = np.array([-0.7, -0.5, -0.0, 0.0, +0.0, 0.3, 1.5, 0.7, float('nan')], dtype=np.float32)
+        def func(x):
+            x_ = tf.round(x)
+            return tf.identity(x_, name=_TFOUTPUT)
+        self._run_test_case(func, [_OUTPUT], {_INPUT: x_val})
+
     @check_opset_min_version(11, "Det")
     @unittest.skip("unclear how this is called in tf-2, fix later")
     def test_determinant(self):

tf2onnx/onnx_opset/math.py

@@ -535,6 +535,15 @@ def version_11(cls, ctx, node, **kwargs):
 
 @tf_op("Round")
 class Round:
+    @classmethod
+    def version_1(cls, ctx, node, **kwargs):
+        # Not exactly nearest even but close enough
+        np_dtype = utils.map_onnx_to_numpy_type(ctx.get_dtype(node.input[0]))
+        const_half = ctx.make_const(utils.make_name("const_half"), np.array(0.5, np_dtype)).output[0]
+        add_node = ctx.make_node("Add", [node.input[0], const_half], op_name_scope=node.name).output[0]
+        node.type = "Floor"
+        ctx.replace_inputs(node, [add_node])
+
     @classmethod
     def version_11(cls, ctx, node, **kwargs):
         pass