[GitHub] [arrow-rs] tustvold commented on a diff in pull request #1871: Add Decimal128 API and use it in DecimalArray and DecimalBuilder

[GitBox <gi...@apache.org>]

tustvold commented on code in PR #1871:
URL: https://github.com/apache/arrow-rs/pull/1871#discussion_r897732642


##########
arrow/src/util/decimal.rs:
##########
@@ -0,0 +1,148 @@
+// Licensed to the Apache Software Foundation (ASF) under one
+// or more contributor license agreements.  See the NOTICE file
+// distributed with this work for additional information
+// regarding copyright ownership.  The ASF licenses this file
+// to you under the Apache License, Version 2.0 (the
+// "License"); you may not use this file except in compliance
+// with the License.  You may obtain a copy of the License at
+//
+//   http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing,
+// software distributed under the License is distributed on an
+// "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+// KIND, either express or implied.  See the License for the
+// specific language governing permissions and limitations
+// under the License.
+
+//! Decimal related utils
+
+use std::cmp::Ordering;
+
+#[derive(Debug)]

Review Comment:
   Perhaps a doc comment or something



##########
arrow/src/util/decimal.rs:
##########
@@ -0,0 +1,148 @@
+// Licensed to the Apache Software Foundation (ASF) under one
+// or more contributor license agreements.  See the NOTICE file
+// distributed with this work for additional information
+// regarding copyright ownership.  The ASF licenses this file
+// to you under the Apache License, Version 2.0 (the
+// "License"); you may not use this file except in compliance
+// with the License.  You may obtain a copy of the License at
+//
+//   http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing,
+// software distributed under the License is distributed on an
+// "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+// KIND, either express or implied.  See the License for the
+// specific language governing permissions and limitations
+// under the License.
+
+//! Decimal related utils
+
+use std::cmp::Ordering;
+
+#[derive(Debug)]
+pub struct Decimal128 {
+    #[allow(dead_code)]
+    precision: usize,
+    scale: usize,
+    value: i128,
+}
+
+impl PartialOrd for Decimal128 {
+    fn partial_cmp(&self, other: &Self) -> Option<Ordering> {
+        assert_eq!(
+            self.scale, other.scale,
+            "Cannot compare two Decimal128 with different scale: {}, {}",
+            self.scale, other.scale
+        );
+        self.value.partial_cmp(&other.value)
+    }
+}
+
+impl Ord for Decimal128 {
+    fn cmp(&self, other: &Self) -> Ordering {
+        assert_eq!(
+            self.scale, other.scale,
+            "Cannot compare two Decimal128 with different scale: {}, {}",
+            self.scale, other.scale
+        );
+        self.value.cmp(&other.value)
+    }
+}
+
+impl PartialEq<Self> for Decimal128 {
+    fn eq(&self, other: &Self) -> bool {
+        assert_eq!(
+            self.scale, other.scale,
+            "Cannot compare two Decimal128 with different scale: {}, {}",
+            self.scale, other.scale
+        );
+        self.value.eq(&other.value)
+    }
+}
+
+impl Eq for Decimal128 {}
+
+impl Decimal128 {
+    pub fn new_from_bytes(precision: usize, scale: usize, bytes: &[u8]) -> Self {
+        let as_array = bytes.try_into();
+        let value = match as_array {
+            Ok(v) if bytes.len() == 16 => i128::from_le_bytes(v),
+            _ => panic!("Input to Decimal128 is not 128bit integer."),
+        };
+
+        Decimal128 {
+            precision,
+            scale,
+            value,
+        }
+    }
+
+    pub fn new_from_i128(precision: usize, scale: usize, value: i128) -> Self {

Review Comment:
   I'm presuming we will want to make Decimal256 and Decimal128 generic versions of the same impl, and so I wonder how methods like this which explicitly name the type will translate? Maybe new_from_raw?



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