emkornfield commented on code in PR #3397: URL: https://github.com/apache/parquet-java/pull/3397#discussion_r3503976300
########## parquet-column/src/main/java/org/apache/parquet/column/values/alp/AlpEncoderDecoder.java: ########## @@ -0,0 +1,359 @@ +/* + * 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 encoding and bit-packing. + * Values that cannot be losslessly converted are stored as exceptions. + * + * <p>Encoding formula: encoded = fastRound(value * POW10[e] * POW10_NEGATIVE[f]) + * <p>Decoding formula: value = encoded * POW10[f] * POW10_NEGATIVE[e] + * + * <p>The order of operations is critical for IEEE 754 correctness. Both formulas must + * be evaluated as single expressions — storing the intermediate multiplication result + * in a variable before the second multiply changes IEEE 754 rounding and produces extra + * exceptions. Uses multiply-by-reciprocal (via POW10_NEGATIVE) for C++ wire compatibility. Review Comment: C++ wire compatibility doesn't make sense to me here, why is it tied to a particular language. Is this something that is missing from the spec for numeric stability, what would the alternative be? -- 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]
