emkornfield commented on code in PR #3390: URL: https://github.com/apache/parquet-java/pull/3390#discussion_r2719715824
########## parquet-column/src/main/java/org/apache/parquet/column/values/alp/AlpValuesReaderForDouble.java: ########## @@ -0,0 +1,202 @@ +/* + * 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.parquet.column.values.alp; + +import static org.apache.parquet.column.values.alp.AlpConstants.*; + +import java.io.IOException; +import java.nio.ByteBuffer; +import java.nio.ByteOrder; +import org.apache.parquet.bytes.ByteBufferInputStream; +import org.apache.parquet.column.values.ValuesReader; +import org.apache.parquet.io.ParquetDecodingException; +import org.slf4j.Logger; +import org.slf4j.LoggerFactory; + +/** + * ALP values reader for DOUBLE type. + * + * <p>Reads ALP-encoded double values from a page and decodes them back to double values. + * + * <p>Page Layout: + * <pre> + * ┌─────────┬────────────────┬────────────────┬─────────────┐ + * │ Header │ AlpInfo Array │ ForInfo Array │ Data Array │ + * │ 8 bytes │ 4B × N vectors │ 9B × N vectors │ Variable │ + * └─────────┴────────────────┴────────────────┴─────────────┘ + * </pre> + */ +public class AlpValuesReaderForDouble extends ValuesReader { + private static final Logger LOG = LoggerFactory.getLogger(AlpValuesReaderForDouble.class); + + // Decoded double values (eagerly decoded) + private double[] decodedValues; + private int currentIndex; + private int totalCount; + + public AlpValuesReaderForDouble() { + this.currentIndex = 0; + this.totalCount = 0; + } + + @Override + public void initFromPage(int valuesCount, ByteBufferInputStream stream) + throws ParquetDecodingException, IOException { + LOG.debug("init from page at offset {} for length {}", stream.position(), stream.available()); + + // Read and validate header + ByteBuffer headerBuf = stream.slice(ALP_HEADER_SIZE).order(ByteOrder.LITTLE_ENDIAN); + int version = headerBuf.get() & 0xFF; + int compressionMode = headerBuf.get() & 0xFF; + int integerEncoding = headerBuf.get() & 0xFF; + int logVectorSize = headerBuf.get() & 0xFF; + int numElements = headerBuf.getInt(); + + if (version != ALP_VERSION) { + throw new ParquetDecodingException("Unsupported ALP version: " + version + ", expected " + ALP_VERSION); + } + if (compressionMode != ALP_COMPRESSION_MODE) { + throw new ParquetDecodingException("Unsupported ALP compression mode: " + compressionMode); + } + if (integerEncoding != ALP_INTEGER_ENCODING_FOR) { + throw new ParquetDecodingException("Unsupported ALP integer encoding: " + integerEncoding); + } + + int vectorSize = 1 << logVectorSize; + int numVectors = (numElements + vectorSize - 1) / vectorSize; + + this.totalCount = numElements; + this.decodedValues = new double[numElements]; + this.currentIndex = 0; + + // Read AlpInfo array + ByteBuffer alpInfoBuf = stream.slice(ALP_INFO_SIZE * numVectors).order(ByteOrder.LITTLE_ENDIAN); + int[] exponents = new int[numVectors]; + int[] factors = new int[numVectors]; + int[] numExceptions = new int[numVectors]; + + for (int v = 0; v < numVectors; v++) { + exponents[v] = alpInfoBuf.get() & 0xFF; + factors[v] = alpInfoBuf.get() & 0xFF; + numExceptions[v] = alpInfoBuf.getShort() & 0xFFFF; + } + + // Read ForInfo array + ByteBuffer forInfoBuf = stream.slice(DOUBLE_FOR_INFO_SIZE * numVectors).order(ByteOrder.LITTLE_ENDIAN); + long[] frameOfReference = new long[numVectors]; + int[] bitWidths = new int[numVectors]; + + for (int v = 0; v < numVectors; v++) { + frameOfReference[v] = forInfoBuf.getLong(); + bitWidths[v] = forInfoBuf.get() & 0xFF; + } + + // Decode each vector + for (int v = 0; v < numVectors; v++) { + int vectorStart = v * vectorSize; + int vectorEnd = Math.min(vectorStart + vectorSize, numElements); + int vectorLen = vectorEnd - vectorStart; + + // Calculate packed data size + int packedBytes = (vectorLen * bitWidths[v] + 7) / 8; + + // Read and unpack values + long[] deltas = new long[vectorLen]; + if (bitWidths[v] > 0) { + ByteBuffer packedBuf = stream.slice(packedBytes).order(ByteOrder.LITTLE_ENDIAN); + unpackLongs(packedBuf, deltas, vectorLen, bitWidths[v]); + } + // else: all deltas are 0 (bitWidth == 0) + + // Reverse FOR and decode Review Comment: nit: spell out FOR? -- This is an automated message from the Apache Git Service. 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