mikemccand commented on a change in pull request #973: LUCENE-9027: Use SIMD instructions to decode postings. URL: https://github.com/apache/lucene-solr/pull/973#discussion_r347144909
########## File path: lucene/core/src/java/org/apache/lucene/codecs/lucene84/ForDeltaUtil.java ########## @@ -0,0 +1,80 @@ +/* + * 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.lucene.codecs.lucene84; + +import java.io.IOException; + +import org.apache.lucene.store.DataInput; +import org.apache.lucene.store.DataOutput; +import org.apache.lucene.util.packed.PackedInts; + +/** + * Utility class to encode/decode increasing sequences of 128 integers. + */ +public class ForDeltaUtil { + + private final ForUtil forUtil; + + ForDeltaUtil(ForUtil forUtil) { + this.forUtil = forUtil; + } + + /** + * Encode deltas of a strictly monotonically increasing sequence of integers. + * The provided {@code longs} are expected to be deltas between consecutive values. + */ + void encodeDeltas(long[] longs, DataOutput out) throws IOException { + if (longs[0] == 1 && PForUtil.allEqual(longs)) { // happens with very dense postings + out.writeByte((byte) 0); + } else { + long or = 0; + for (long l : longs) { + or |= l; + } + assert or != 0; + final int bitsPerValue = PackedInts.bitsRequired(or); + out.writeByte((byte) bitsPerValue); + forUtil.encode(longs, bitsPerValue, out); + } + } + + /** + * Decode deltas, compute the prefix sum and add {@code base} to all decoded longs. + */ + void decodeAndPrefixSum(DataInput in, long base, long[] longs) throws IOException { + final int bitsPerValue = Byte.toUnsignedInt(in.readByte()); + if (bitsPerValue == 0) { + // Note: can this special-case be optimized? Review comment: Maybe hotspot is able to SIMD this loop? ---------------------------------------------------------------- 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. For queries about this service, please contact Infrastructure at: us...@infra.apache.org With regards, Apache Git Services --------------------------------------------------------------------- To unsubscribe, e-mail: issues-unsubscr...@lucene.apache.org For additional commands, e-mail: issues-h...@lucene.apache.org
