emkornfield commented on code in PR #3390: URL: https://github.com/apache/parquet-java/pull/3390#discussion_r2719351532
########## parquet-column/src/main/java/org/apache/parquet/column/values/alp/AlpEncoderDecoder.java: ########## @@ -0,0 +1,384 @@ +/* + * 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.*; + +/** + * Core ALP (Adaptive Lossless floating-Point) encoding and decoding logic. + * + * <p>ALP works by converting floating-point values to integers using decimal scaling, + * then applying Frame of Reference (FOR) encoding and bit-packing. + * Values that cannot be losslessly converted are stored as exceptions. + * + * <p>Encoding formula: encoded = round(value * 10^(exponent - factor)) + * <p>Decoding formula: value = encoded / 10^(exponent - factor) + * + * <p>Exception conditions: + * <ul> + * <li>NaN values</li> + * <li>Infinity values</li> + * <li>Negative zero (-0.0)</li> + * <li>Out of integer range</li> + * <li>Round-trip failure (decode(encode(v)) != v)</li> + * </ul> + */ +public final class AlpEncoderDecoder { + + private AlpEncoderDecoder() { + // Utility class + } + + // ========== Float Encoding/Decoding ========== + + /** + * Check if a float value is an exception (cannot be losslessly encoded). + * + * @param value the float value to check + * @return true if the value is an exception + */ + public static boolean isFloatException(float value) { + // NaN check + if (Float.isNaN(value)) { + return true; + } + // Infinity check + if (Float.isInfinite(value)) { + return true; + } + // Negative zero check + if (Float.floatToRawIntBits(value) == FLOAT_NEGATIVE_ZERO_BITS) { + return true; + } + return false; + } + + /** + * Check if a float value will be an exception for the given exponent/factor. + * + * @param value the float value + * @param exponent the decimal exponent (0-10) + * @param factor the decimal factor (0 <= factor <= exponent) + * @return true if the value is an exception for this encoding + */ + public static boolean isFloatException(float value, int exponent, int factor) { + if (isFloatException(value)) { + return true; + } + + // Try encoding and check for round-trip failure + float multiplier = FLOAT_POW10[exponent]; + if (factor > 0) { + multiplier /= FLOAT_POW10[factor]; + } + + float scaled = value * multiplier; + + // Check for overflow + if (scaled > Integer.MAX_VALUE || scaled < Integer.MIN_VALUE) { + return true; + } + + // Fast round + int encoded = fastRoundFloat(scaled); + + // Check round-trip + float decoded = encoded / multiplier; + return Float.floatToRawIntBits(value) != Float.floatToRawIntBits(decoded); + } + + /** + * Encode a float value to an integer using the specified exponent and factor. + * + * <p>Formula: encoded = round(value * 10^(exponent - factor)) + * + * @param value the float value to encode + * @param exponent the decimal exponent (0-10) + * @param factor the decimal factor (0 <= factor <= exponent) + * @return the encoded integer value + */ + public static int encodeFloat(float value, int exponent, int factor) { + float multiplier = FLOAT_POW10[exponent]; + if (factor > 0) { + multiplier /= FLOAT_POW10[factor]; + } + return fastRoundFloat(value * multiplier); + } + + /** + * Decode an integer back to a float using the specified exponent and factor. + * + * <p>Formula: value = encoded / 10^(exponent - factor) + * + * @param encoded the encoded integer value + * @param exponent the decimal exponent (0-10) + * @param factor the decimal factor (0 <= factor <= exponent) + * @return the decoded float value + */ + public static float decodeFloat(int encoded, int exponent, int factor) { + float multiplier = FLOAT_POW10[exponent]; + if (factor > 0) { + multiplier /= FLOAT_POW10[factor]; + } + return encoded / multiplier; + } + + /** + * Fast rounding for float values using the magic number technique. + * + * @param value the float value to round + * @return the rounded integer value + */ + public static int fastRoundFloat(float value) { + if (value >= 0) { + return (int) ((value + MAGIC_FLOAT) - MAGIC_FLOAT); + } else { + return (int) ((value - MAGIC_FLOAT) + MAGIC_FLOAT); + } + } + + // ========== Double Encoding/Decoding ========== + + /** + * Check if a double value is an exception (cannot be losslessly encoded). + * + * @param value the double value to check + * @return true if the value is an exception + */ + public static boolean isDoubleException(double value) { + // NaN check + if (Double.isNaN(value)) { + return true; + } + // Infinity check + if (Double.isInfinite(value)) { + return true; + } + // Negative zero check + if (Double.doubleToRawLongBits(value) == DOUBLE_NEGATIVE_ZERO_BITS) { + return true; + } + return false; + } + + /** + * Check if a double value will be an exception for the given exponent/factor. + * + * @param value the double value + * @param exponent the decimal exponent (0-18) + * @param factor the decimal factor (0 <= factor <= exponent) + * @return true if the value is an exception for this encoding + */ + public static boolean isDoubleException(double value, int exponent, int factor) { + if (isDoubleException(value)) { + return true; + } + + // Try encoding and check for round-trip failure + double multiplier = DOUBLE_POW10[exponent]; + if (factor > 0) { + multiplier /= DOUBLE_POW10[factor]; + } + + double scaled = value * multiplier; + + // Check for overflow + if (scaled > Long.MAX_VALUE || scaled < Long.MIN_VALUE) { + return true; + } + + // Fast round + long encoded = fastRoundDouble(scaled); + + // Check round-trip + double decoded = encoded / multiplier; + return Double.doubleToRawLongBits(value) != Double.doubleToRawLongBits(decoded); + } + + /** + * Encode a double value to a long using the specified exponent and factor. + * + * <p>Formula: encoded = round(value * 10^(exponent - factor)) + * + * @param value the double value to encode + * @param exponent the decimal exponent (0-18) + * @param factor the decimal factor (0 <= factor <= exponent) + * @return the encoded long value + */ + public static long encodeDouble(double value, int exponent, int factor) { + double multiplier = DOUBLE_POW10[exponent]; + if (factor > 0) { + multiplier /= DOUBLE_POW10[factor]; + } + return fastRoundDouble(value * multiplier); + } + + /** + * Decode a long back to a double using the specified exponent and factor. + * + * <p>Formula: value = encoded / 10^(exponent - factor) + * + * @param encoded the encoded long value + * @param exponent the decimal exponent (0-18) + * @param factor the decimal factor (0 <= factor <= exponent) + * @return the decoded double value + */ + public static double decodeDouble(long encoded, int exponent, int factor) { + double multiplier = DOUBLE_POW10[exponent]; + if (factor > 0) { + multiplier /= DOUBLE_POW10[factor]; + } + return encoded / multiplier; + } + + /** + * Fast rounding for double values using the magic number technique. + * + * @param value the double value to round + * @return the rounded long value + */ + public static long fastRoundDouble(double value) { + if (value >= 0) { + return (long) ((value + MAGIC_DOUBLE) - MAGIC_DOUBLE); + } else { + return (long) ((value - MAGIC_DOUBLE) + MAGIC_DOUBLE); + } + } + + // ========== Bit Width Calculation ========== + + /** + * Calculate the bit width needed to store unsigned values up to maxDelta. + * + * @param maxDelta the maximum delta value (unsigned) + * @return the number of bits needed (0-32 for int, 0-64 for long) Review Comment: long is not covered here. -- This is an automated message from the Apache Git Service. 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