fix(mge/clamp): fix `F.clamp`

GitOrigin-RevId: 1efac8add61819630895cb29ca4d607c94b040d1

python_module/megengine/functional/elemwise.py

@@ -233,9 +233,11 @@ def clamp(inp: Tensor, lower=None, upper=None) -> Tensor:
         [0 1 2 3 3]
 
     """
-    assert lower or upper, "At least one of 'lower' or 'upper' must not be None"
-    if lower:
-        if upper:
+    assert (
+        lower is not None or upper is not None
+    ), "At least one of 'lower' or 'upper' must not be None"
+    if lower is not None:
+        if upper is not None:
             assert lower <= upper, "clamp lower bound is bigger that upper bound"
             return minimum(maximum(inp, lower), upper)
         else:

python_module/test/unit/functional/test_elemwise.py

@@ -44,3 +44,12 @@ def test_multiply():
             np.array([3.0, 4.0], dtype=np.float32),
         ),
     )
+
+
+def test_clamp():
+    """Fix an issue when `lower` or `upper` is 0, it will be recognized as `False` and
+    `F.clamp` will fall into wrong conditions unexpectedly.
+    """
+    x = np.linspace(-6, 6, dtype="float32")
+    assertTensorClose(F.clamp(tensor(x) + 3, 0, 6).numpy(), np.clip(x + 3, 0, 6))
+    assertTensorClose(F.clamp(tensor(x) - 3, -6, 0).numpy(), np.clip(x - 3, -6, 0))