Merge pull request #3191 from beam2d/no-cast

Make F.cast return the input as is if no cast is needed

chainer/functions/array/cast.py

@@ -1,3 +1,4 @@
+import chainer
 from chainer import function_node
 from chainer.utils import type_check
 
@@ -50,4 +51,6 @@ def cast(x, typ):
         dtype('float16')
 
     """
+    if x.dtype == typ:
+        return chainer.as_variable(x)
     return Cast(typ).apply((x,))[0]

tests/chainer_tests/functions_tests/array_tests/test_cast.py

@@ -57,4 +57,26 @@ def test_backward_cpu(self):
         self.check_backward(self.x, self.g)
 
 
+class TestNoCast(unittest.TestCase):
+
+    def setUp(self):
+        self.dtype = numpy.float32
+        self.x = numpy.empty(1, self.dtype)
+
+    def check_forward_no_cast(self, x_data):
+        y = functions.cast(x_data, self.dtype)
+        self.assertIsInstance(y, chainer.Variable)
+        self.assertIs(y.data, x_data)
+
+    def test_forward_no_cast_array(self):
+        y = functions.cast(self.x, self.dtype)
+        self.assertIsInstance(y, chainer.Variable)
+        self.assertIs(y.data, self.x)
+
+    def test_forward_no_cast_variable(self):
+        x = chainer.Variable(self.x)
+        y = functions.cast(x, self.dtype)
+        self.assertIs(y, x)
+
+
 testing.run_module(__name__, __file__)