[GitHub] [iceberg] emkornfield commented on a change in pull request #3966: Core: Adds Utility Class for Implementing ZOrdering

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emkornfield commented on a change in pull request #3966:
URL: https://github.com/apache/iceberg/pull/3966#discussion_r793249899



##########
File path: core/src/main/java/org/apache/iceberg/util/ZOrderByteUtils.java
##########
@@ -0,0 +1,128 @@
+/*
+ * 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.
+ */
+
+package org.apache.iceberg.util;
+
+import java.util.Arrays;
+
+/**
+ * Within Z-Ordering the byte representations of objects being compared must be ordered,
+ * this requires several types to be transformed when converted to bytes. The goal is to
+ * map object's whose byte representation are not lexicographically ordered into representations
+ * that are lexicographically ordered.
+ * Most of these techniques are derived from
+ * https://aws.amazon.com/blogs/database/z-order-indexing-for-multifaceted-queries-in-amazon-dynamodb-part-2/
+ */
+public class ZOrderByteUtils {
+
+  private ZOrderByteUtils() {
+
+  }
+
+  /**
+   * Signed ints do not have their bytes in magnitude order because of the sign bit.
+   * To fix this, flip the sign bit so that all negatives are ordered before positives. This essentially
+   * shifts the 0 value so that we don't break our ordering when we cross the new 0 value.
+   */
+  public static byte[] orderIntLikeBytes(byte[] intBytes, int size) {

Review comment:
       is it worth documenting assumed endianness and contract for nulls (always first in the sort order?)




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