Merge pull request #19621 from seberg/fix-normal-ufunc-safety

BUG: The normal cast-safety for ufunc loops is "no" casting

2 files changed, 33 insertions, 2 deletions

diff --git a/numpy/core/src/umath/legacy_array_method.c b/numpy/core/src/umath/legacy_array_method.c
index a5e123baa..4351f1d25 100644
--- a/numpy/core/src/umath/legacy_array_method.c
+++ b/numpy/core/src/umath/legacy_array_method.c
@@ -142,7 +142,7 @@ simple_legacy_resolve_descriptors(
         }
     }
 
-    return NPY_SAFE_CASTING;
+    return NPY_NO_CASTING;
 
   fail:
     for (int i = 0; i < nin + nout; i++) {
@@ -244,7 +244,7 @@ PyArray_NewLegacyWrappingArrayMethod(PyUFuncObject *ufunc,
         .dtypes = signature,
         .flags = flags,
         .slots = slots,
-        .casting = NPY_EQUIV_CASTING,
+        .casting = NPY_NO_CASTING,
     };
 
     PyBoundArrayMethodObject *bound_res = PyArrayMethod_FromSpec_int(&spec, 1);
diff --git a/numpy/core/tests/test_ufunc.py b/numpy/core/tests/test_ufunc.py
index 657b6a79b..c3ea10d93 100644
--- a/numpy/core/tests/test_ufunc.py
+++ b/numpy/core/tests/test_ufunc.py
@@ -536,6 +536,37 @@ class TestUfunc:
         np.add(arr, arr, dtype="m")
         np.maximum(arr, arr, dtype="m")
 
+    @pytest.mark.parametrize("ufunc", [np.add, np.sqrt])
+    def test_cast_safety(self, ufunc):
+        """Basic test for the safest casts, because ufuncs inner loops can
+        indicate a cast-safety as well (which is normally always "no").
+        """
+        def call_ufunc(arr, **kwargs):
+            return ufunc(*(arr,) * ufunc.nin, **kwargs)
+
+        arr = np.array([1., 2., 3.], dtype=np.float32)
+        arr_bs = arr.astype(arr.dtype.newbyteorder())
+        expected = call_ufunc(arr)
+        # Normally, a "no" cast:
+        res = call_ufunc(arr, casting="no")
+        assert_array_equal(expected, res)
+        # Byte-swapping is not allowed with "no" though:
+        with pytest.raises(TypeError):
+            call_ufunc(arr_bs, casting="no")
+
+        # But is allowed with "equiv":
+        res = call_ufunc(arr_bs, casting="equiv")
+        assert_array_equal(expected, res)
+
+        # Casting to float64 is safe, but not equiv:
+        with pytest.raises(TypeError):
+            call_ufunc(arr_bs, dtype=np.float64, casting="equiv")
+
+        # but it is safe cast:
+        res = call_ufunc(arr_bs, dtype=np.float64, casting="safe")
+        expected = call_ufunc(arr.astype(np.float64))  # upcast
+        assert_array_equal(expected, res)
+
     def test_true_divide(self):
         a = np.array(10)
         b = np.array(20)