| /* |
| * 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.util.packed; |
| |
| |
| import static org.apache.lucene.util.packed.MonotonicBlockPackedReader.expected; |
| |
| import java.io.IOException; |
| |
| import org.apache.lucene.store.DataOutput; |
| import org.apache.lucene.util.BitUtil; |
| |
| /** |
| * A writer for large monotonically increasing sequences of positive longs. |
| * <p> |
| * The sequence is divided into fixed-size blocks and for each block, values |
| * are modeled after a linear function f: x → A × x + B. The block |
| * encodes deltas from the expected values computed from this function using as |
| * few bits as possible. |
| * <p> |
| * Format: |
| * <ul> |
| * <li><BLock><sup>BlockCount</sup> |
| * <li>BlockCount: ⌈ ValueCount / BlockSize ⌉ |
| * <li>Block: <Header, (Ints)> |
| * <li>Header: <B, A, BitsPerValue> |
| * <li>B: the B from f: x → A × x + B using a |
| * {@link BitUtil#zigZagEncode(long) zig-zag encoded} |
| * {@link DataOutput#writeVLong(long) vLong} |
| * <li>A: the A from f: x → A × x + B encoded using |
| * {@link Float#floatToIntBits(float)} on |
| * {@link DataOutput#writeInt(int) 4 bytes} |
| * <li>BitsPerValue: a {@link DataOutput#writeVInt(int) variable-length int} |
| * <li>Ints: if BitsPerValue is <tt>0</tt>, then there is nothing to read and |
| * all values perfectly match the result of the function. Otherwise, these |
| * are the {@link PackedInts packed} deltas from the expected value |
| * (computed from the function) using exactly BitsPerValue bits per value. |
| * </ul> |
| * @see MonotonicBlockPackedReader |
| * @lucene.internal |
| */ |
| public final class MonotonicBlockPackedWriter extends AbstractBlockPackedWriter { |
| |
| /** |
| * Sole constructor. |
| * @param blockSize the number of values of a single block, must be a power of 2 |
| */ |
| public MonotonicBlockPackedWriter(DataOutput out, int blockSize) { |
| super(out, blockSize); |
| } |
| |
| @Override |
| public void add(long l) throws IOException { |
| assert l >= 0; |
| super.add(l); |
| } |
| |
| protected void flush() throws IOException { |
| assert off > 0; |
| |
| final float avg = off == 1 ? 0f : (float) (values[off - 1] - values[0]) / (off - 1); |
| long min = values[0]; |
| // adjust min so that all deltas will be positive |
| for (int i = 1; i < off; ++i) { |
| final long actual = values[i]; |
| final long expected = expected(min, avg, i); |
| if (expected > actual) { |
| min -= (expected - actual); |
| } |
| } |
| |
| long maxDelta = 0; |
| for (int i = 0; i < off; ++i) { |
| values[i] = values[i] - expected(min, avg, i); |
| maxDelta = Math.max(maxDelta, values[i]); |
| } |
| |
| out.writeZLong(min); |
| out.writeInt(Float.floatToIntBits(avg)); |
| if (maxDelta == 0) { |
| out.writeVInt(0); |
| } else { |
| final int bitsRequired = PackedInts.bitsRequired(maxDelta); |
| out.writeVInt(bitsRequired); |
| writeValues(bitsRequired); |
| } |
| |
| off = 0; |
| } |
| |
| } |