Try to detect bug in nvcc.

theano/sandbox/cuda/tests/test_driver.py

@@ -69,5 +69,24 @@ def test_nvidia_driver3():
     assert any([isinstance(node.op, cuda.GpuElemwise) for node in topo])
     assert theano.sandbox.cuda.use.device_number is not None
 
+
+def test_nvcc_cast():
+    """Test that the casting behaviour is correct.
+
+    Some versions of nvcc, in particular the one in 6.5.14, return an incorrect
+    value in this case.
+
+    Reported by Zijung Zhang at
+    https://groups.google.com/d/topic/theano-dev/LzHtP2OWeRE/discussion
+    """
+    var = theano.tensor.fvector()
+    f = theano.function([var], -1. * (var > 0), mode=mode_with_gpu)
+    if not numpy.allclose(f([-1, 0, 1]), [0, 0, -1]):
+        raise Exception(
+            "The version of nvcc that Theano detected on your system "
+            "has a bug during conversion from integers to floating point. "
+            "Installing CUDA 7.0 (or more recent) should fix the problem.")
+
+
 # TODO make sure the test_nvidia_driver test are executed when we make manually
 # a CudaNdarray like this: cuda.CudaNdarray.zeros((5,4))