Add dpnp.common_type implementation

dpnp/dpnp_iface.py

@@ -61,6 +61,7 @@
     "as_usm_ndarray",
     "check_limitations",
     "check_supported_arrays_type",
+    "common_type",
     "default_float_type",
     "from_dlpack",
     "get_dpnp_descriptor",
@@ -406,6 +407,73 @@ def check_supported_arrays_type(*arrays, scalar_type=False, all_scalars=False):
     return True
 
 
+# determine the "minimum common type" for a group of arrays
+array_precision = {
+    dpnp.float16: 0,
+    dpnp.float32: 1,
+    dpnp.float64: 2,
+    dpnp.complex64: 3,
+    dpnp.complex128: 4,
+}
+
+array_type = {
+    "float": {0: dpnp.float16, 1: dpnp.float32, 2: dpnp.float64},
+    "complex": {3: dpnp.complex64, 4: dpnp.complex128},
+}
+
+
+def common_type(*arrays):
+    """
+    Return a scalar type which is common to the input arrays.
+
+    The return type will always be an inexact (i.e. floating point) scalar
+    type, even if all the arrays are integer arrays. If one of the inputs is
+    an integer array, the minimum precision type that is returned is a
+    64-bit floating point dtype.
+
+    For full documentation refer to :obj:`numpy.common_type`
+
+    Parameters
+    ----------
+    array1, array2, ... : {dpnp.ndarray, usm_ndarray}
+        Input arrays.
+
+    Returns
+    -------
+    out : data type code
+        Data type code.
+
+    Examples
+    --------
+    >>> import dpnp as np
+    >>> np.common_type(np.arange(2, dtype=np.float32))
+    <class 'numpy.float32'>
+    >>> np.common_type(np.arange(2, dtype=np.float32), np.arange(2))
+    <class 'numpy.float64'>
+    >>> np.common_type(np.arange(4), np.array([45, 6.j]), np.array([45.0]))
+    <class 'numpy.complex128'>
+
+    """
+    dpnp.check_supported_arrays_type(*arrays)
+
+    is_complex = False
+    max_precision = 0
+
+    for a in arrays:
+        t = a.dtype.type
+
+        if dpnp.issubdtype(t, dpnp.complexfloating):
+            is_complex = True
+        if dpnp.issubdtype(t, dpnp.integer):
+            t = dpnp.float64
+
+        max_precision = max(max_precision, array_precision.get(t, 0))
+
+    if is_complex:
+        return array_type["complex"].get(max_precision, dpnp.complex128)
+    return array_type["float"].get(max_precision, dpnp.float64)
+
+
 def default_float_type(device=None, sycl_queue=None):
     """
     Return a floating type used by default in DPNP depending on device

tests/third_party/cupy/test_type_routines.py

@@ -46,7 +46,6 @@ def test_can_cast(self, xp, from_dtype, to_dtype):
         return ret
 
 
-@pytest.mark.skip("dpnp.common_type() is not implemented yet")
 class TestCommonType(unittest.TestCase):
     @testing.numpy_cupy_equal()
     def test_common_type_empty(self, xp):