Implement dpnp.common_type() (#2391)

This PR suggests adding an implementation of `dpnp.common_type()` and
updates cupy `TestCommonType` tests.

Author: vlad-perevezentsev

dpnp/dpnp_iface_types.py

@@ -32,16 +32,25 @@
 This module provides public type interface file for the library
 """
 
+import functools
+
+import dpctl
 import dpctl.tensor as dpt
 import numpy
 
+import dpnp
+
 from .dpnp_array import dpnp_array
 
+# pylint: disable=no-name-in-module
+from .dpnp_utils import get_usm_allocations
+
 __all__ = [
     "bool",
     "bool_",
     "byte",
     "cdouble",
+    "common_type",
     "complex128",
     "complex64",
     "complexfloating",
@@ -145,6 +154,67 @@
 pi = numpy.pi
 
 
+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 or complex)
+    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 the default floating point data type for the device
+    where the input arrays are allocated.
+
+    For full documentation refer to :obj:`numpy.common_type`.
+
+    Parameters
+    ----------
+    arrays: {dpnp.ndarray, usm_ndarray}
+        Input arrays.
+
+    Returns
+    -------
+    out: data type
+        Data type object.
+
+    See Also
+    --------
+    :obj:`dpnp.dtype` : Create a data type object.
+
+    Examples
+    --------
+    >>> import dpnp as np
+    >>> np.common_type(np.arange(2, dtype=np.float32))
+    numpy.float32
+    >>> np.common_type(np.arange(2, dtype=np.float32), np.arange(2))
+    numpy.float64 # may vary
+    >>> np.common_type(np.arange(4), np.array([45, 6.j]), np.array([45.0]))
+    numpy.complex128 # may vary
+
+    """
+
+    if len(arrays) == 0:
+        return (
+            dpnp.float16
+            if dpctl.select_default_device().has_aspect_fp16
+            else dpnp.float32
+        )
+
+    dpnp.check_supported_arrays_type(*arrays)
+
+    _, exec_q = get_usm_allocations(arrays)
+    default_float_dtype = dpnp.default_float_type(sycl_queue=exec_q)
+    dtypes = []
+    for a in arrays:
+        if not dpnp.issubdtype(a.dtype, dpnp.number):
+            raise TypeError("can't get common type for non-numeric array")
+        if dpnp.issubdtype(a.dtype, dpnp.integer):
+            dtypes.append(default_float_dtype)
+        else:
+            dtypes.append(a.dtype)
+
+    return functools.reduce(numpy.promote_types, dtypes).type
+
+
 # pylint: disable=redefined-outer-name
 def finfo(dtype):
     """

dpnp/tests/third_party/cupy/test_type_routines.py

@@ -4,7 +4,7 @@
 import pytest
 
 import dpnp as cupy
-from dpnp.tests.helper import has_support_aspect64
+from dpnp.tests.helper import has_support_aspect16, has_support_aspect64
 from dpnp.tests.third_party.cupy import testing
 
 
@@ -47,13 +47,17 @@ 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):
         ret = xp.common_type()
         assert type(ret) is type
+        # NumPy always returns float16 for empty input,
+        # but dpnp returns float32 if the device does not support
+        # 16-bit precision floating point operations
+        if xp is numpy and not has_support_aspect16():
+            return xp.float32
         return ret
 
     @testing.for_all_dtypes(no_bool=True)
@@ -62,6 +66,11 @@ def test_common_type_single_argument(self, xp, dtype):
         array = _generate_type_routines_input(xp, dtype, "array")
         ret = xp.common_type(array)
         assert type(ret) is type
+        # NumPy promotes integer types to float64,
+        # but dpnp may return float32 if the device does not support
+        # 64-bit precision floating point operations.
+        if xp is numpy and not has_support_aspect64():
+            return xp.float32
         return ret
 
     @testing.for_all_dtypes_combination(
@@ -73,6 +82,8 @@ def test_common_type_two_arguments(self, xp, dtype1, dtype2):
         array2 = _generate_type_routines_input(xp, dtype2, "array")
         ret = xp.common_type(array1, array2)
         assert type(ret) is type
+        if xp is numpy and not has_support_aspect64():
+            return xp.float32
         return ret
 
     @testing.for_all_dtypes()