rdblue commented on a change in pull request #3966: URL: https://github.com/apache/iceberg/pull/3966#discussion_r800252771
########## File path: core/src/main/java/org/apache/iceberg/util/ZOrderByteUtils.java ########## @@ -0,0 +1,162 @@ +/* + * 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.nio.ByteBuffer; +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/ + * + * Some implementation is taken from + * https://github.com/apache/hbase/blob/master/hbase-common/src/main/java/org/apache/hadoop/hbase/util/OrderedBytes.java + */ +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[] intToOrderedBytes(int val) { + ByteBuffer bytes = ByteBuffer.allocate(Integer.BYTES); + bytes.putInt(val ^ 0x80000000); + return bytes.array(); + } + + /** + * Signed longs are treated the same as the signed ints + */ + public static byte[] longToOrderBytes(long val) { + ByteBuffer bytes = ByteBuffer.allocate(Long.BYTES); + bytes.putLong(val ^ 0x8000000000000000L); + return bytes.array(); + } + + /** + * Signed shorts are treated the same as the signed ints + */ + public static byte[] shortToOrderBytes(short val) { + ByteBuffer bytes = ByteBuffer.allocate(Short.BYTES); + bytes.putShort((short) (val ^ (0x8000))); + return bytes.array(); + } + + /** + * Signed tiny ints are treated the same as the signed ints + */ + public static byte[] tinyintToOrderedBytes(byte val) { + ByteBuffer bytes = ByteBuffer.allocate(Byte.BYTES); + bytes.put((byte) (val ^ (0x80))); + return bytes.array(); + } + + /** + * IEEE 754 : + * “If two floating-point numbers in the same format are ordered (say, x {@literal <} 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[] floatToOrderedBytes(float val) { + ByteBuffer bytes = ByteBuffer.allocate(Integer.BYTES); + int ival = Float.floatToIntBits(val); + ival ^= ((ival >> (Integer.SIZE - 1)) | Integer.MIN_VALUE); + bytes.putInt(ival); + return bytes.array(); + } + + /** + * Doubles are treated the same as floats + */ + public static byte[] doubleToOrderedBytes(double val) { + ByteBuffer bytes = ByteBuffer.allocate(Long.BYTES); + long lng = Double.doubleToLongBits(val); + lng ^= ((lng >> (Long.SIZE - 1)) | Long.MIN_VALUE); + bytes.putLong(lng); + return bytes.array(); + } + + /** + * Strings are lexicographically sortable BUT if different byte array lengths will + * ruin the Z-Ordering. (ZOrder requires that a given column contribute the same number of bytes every time). + * This implementation just uses a set size to for all output byte representations. Truncating longer strings + * and right padding 0 for shorter strings. + */ + public static byte[] stringToOrderedBytes(String val, int length) { + ByteBuffer bytes = ByteBuffer.allocate(length); + if (val != null) { + int maxLength = Math.min(length, val.length()); + bytes.put(val.getBytes(), 0, maxLength); + } + return bytes.array(); + } + + /** + * Interleave bits using a naive loop. + * @param columnsBinary an array of byte arrays, none of which are empty + * @return their bits interleaved + */ + public static byte[] interleaveBits(byte[][] columnsBinary) { + int interleavedSize = Arrays.stream(columnsBinary).mapToInt(a -> a.length).sum(); + byte[] interleavedBytes = new byte[interleavedSize]; + int sourceBit = 7; + int sourceByte = 0; + int sourceColumn = 0; + int interleaveBit = 7; + int interleaveByte = 0; + while (interleaveByte < interleavedSize) { + // Take what we have, Get the source Bit of the source Byte, move it to the interleaveBit position + interleavedBytes[interleaveByte] = + (byte) (interleavedBytes[interleaveByte] | + (columnsBinary[sourceColumn][sourceByte] & 1 << sourceBit) >> sourceBit << interleaveBit); + + --interleaveBit; + if (interleaveBit == -1) { + // Finished a byte in our interleave byte array start a new byte + interleaveByte++; + interleaveBit = 7; + } + + // Find next column with a byte we can use + do { + ++sourceColumn; + if (sourceColumn == columnsBinary.length) { + sourceColumn = 0; + if (--sourceBit == -1) { Review comment: I think it's much easier to read and reason about algorithms like this if you don't use the return value of ++ or -- operators. -- This is an automated message from the Apache Git Service. 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