| /* |
| * 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.backward_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 { |
| |
| // IDENTITY_PLUS_ONE[i] == i+1 |
| private static final long[] IDENTITY_PLUS_ONE = new long[ForUtil.BLOCK_SIZE]; |
| |
| static { |
| for (int i = 0; i < ForUtil.BLOCK_SIZE; ++i) { |
| IDENTITY_PLUS_ONE[i] = i + 1; |
| } |
| } |
| |
| private static void prefixSumOfOnes(long[] arr, long base) { |
| System.arraycopy(IDENTITY_PLUS_ONE, 0, arr, 0, ForUtil.BLOCK_SIZE); |
| // This loop gets auto-vectorized |
| for (int i = 0; i < ForUtil.BLOCK_SIZE; ++i) { |
| arr[i] += base; |
| } |
| } |
| |
| 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) { |
| prefixSumOfOnes(longs, base); |
| } else { |
| forUtil.decodeAndPrefixSum(bitsPerValue, in, base, longs); |
| } |
| } |
| |
| /** Skip a sequence of 128 longs. */ |
| void skip(DataInput in) throws IOException { |
| final int bitsPerValue = Byte.toUnsignedInt(in.readByte()); |
| if (bitsPerValue != 0) { |
| in.skipBytes(forUtil.numBytes(bitsPerValue)); |
| } |
| } |
| } |