Enable rounding for Decimal32 and Decimal64 in cuDF (#17332)

Authors:
  - Hirota Akio (https://github.com/a-hirota)
  - Vyas Ramasubramani (https://github.com/vyasr)

Approvers:
  - Matthew Roeschke (https://github.com/mroeschke)

URL: #17332

python/cudf/cudf/core/indexed_frame.py

@@ -3970,7 +3970,13 @@ def round(self, decimals=0, how="half_even"):
 
         cols = (
             col.round(decimals[name], how=how)
-            if name in decimals and col.dtype.kind in "fiu"
+            if name in decimals
+            and (
+                col.dtype.kind in "fiu"
+                or isinstance(
+                    col.dtype, (cudf.Decimal32Dtype, cudf.Decimal64Dtype)
+                )
+            )
             else col.copy(deep=True)
             for name, col in self._column_labels_and_values
         )

python/cudf/cudf/tests/test_series.py

@@ -772,6 +772,69 @@ def test_round_nan_as_null_false(series, decimal):
     assert_eq(result, expected, atol=1e-10)
 
 
+@pytest.mark.parametrize(
+    "data, dtype, decimals, expected_half_up, expected_half_even",
+    [
+        (
+            [1.234, 2.345, 3.456],
+            cudf.Decimal32Dtype(precision=5, scale=3),
+            2,
+            [1.23, 2.35, 3.46],
+            [1.23, 2.34, 3.46],
+        ),
+        (
+            [1.234, 2.345, 3.456],
+            cudf.Decimal32Dtype(precision=5, scale=3),
+            0,
+            [1.0, 2.0, 3.0],
+            [1.0, 2.0, 3.0],
+        ),
+        (
+            [1.234, 2.345, 3.456],
+            cudf.Decimal32Dtype(precision=5, scale=3),
+            3,
+            [1.234, 2.345, 3.456],
+            [1.234, 2.345, 3.456],
+        ),
+        (
+            [1.234567, 2.345678, 3.456789],
+            cudf.Decimal64Dtype(precision=10, scale=6),
+            4,
+            [1.2346, 2.3457, 3.4568],
+            [1.2346, 2.3457, 3.4568],
+        ),
+        (
+            [1.234567, 2.345678, 3.456789],
+            cudf.Decimal64Dtype(precision=10, scale=6),
+            2,
+            [1.23, 2.35, 3.46],
+            [1.23, 2.35, 3.46],
+        ),
+        (
+            [1.234567, 2.345678, 3.456789],
+            cudf.Decimal64Dtype(precision=10, scale=6),
+            6,
+            [1.234567, 2.345678, 3.456789],
+            [1.234567, 2.345678, 3.456789],
+        ),
+    ],
+)
+def test_series_round_decimal(
+    data, dtype, decimals, expected_half_up, expected_half_even
+):
+    ser = cudf.Series(data).astype(dtype)
+
+    result_half_up = ser.round(decimals=decimals, how="half_up").astype(dtype)
+    expected_ser_half_up = cudf.Series(expected_half_up).astype(dtype)
+    assert_eq(result_half_up, expected_ser_half_up)
+
+    result_half_even = ser.round(decimals=decimals, how="half_even").astype(
+        dtype
+    )
+    expected_ser_half_even = cudf.Series(expected_half_even).astype(dtype)
+    assert_eq(result_half_even, expected_ser_half_even)
+
+
 @pytest.mark.parametrize("ps", _series_na_data())
 @pytest.mark.parametrize("nan_as_null", [True, False, None])
 def test_series_isnull_isna(ps, nan_as_null):