RussellSpitzer commented on a change in pull request #3966: URL: https://github.com/apache/iceberg/pull/3966#discussion_r795309778
########## 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) { + if (intBytes == null) { + return new byte[size]; + } + intBytes[0] = (byte) (intBytes[0] ^ (1 << 7)); + return intBytes; + } + + /** + * IEEE 754 : + * “If two floating-point numbers in the same format are ordered (say, x \< y), + * they are ordered the same way when their bits are reinterpreted as sign-magnitude integers.” + * + * Which means floats can be treated as sign magnitude integers which can then be converted into lexicographically + * comparable bytes + */ + public static byte[] orderFloatLikeBytes(byte[] floatBytes, int size) { Review comment: Actually I think I can still do this with duds for the prototype, Will code all this up Monday -- This is an automated message from the Apache Git Service. To respond to the message, please log on to GitHub and use the URL above to go to the specific comment. To unsubscribe, e-mail: [email protected] For queries about this service, please contact Infrastructure at: [email protected] --------------------------------------------------------------------- To unsubscribe, e-mail: [email protected] For additional commands, e-mail: [email protected]
