package org.apache.lucene.util.encoding;
import java.io.IOException;
/*
* 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.
*/
/**
* A {@link ChunksIntEncoder} which encodes data in chunks of 8. Every group starts with a single
* byte (called indicator) which represents 8 - 1 bit flags, where the value:
* <ul>
* <li>1 means the encoded value is '1'
* <li>0 means the value is encoded using {@link VInt8IntEncoder}, and the
* encoded bytes follow the indicator.<br>
* Since value 0 is illegal, and 1 is encoded in the indicator, the actual
* value that is encoded is <code>value-2</code>, which saves some more bits.
* </ul>
* Encoding example:
* <ul>
* <li>Original values: 6, 16, 5, 9, 7, 1
* <li>After sorting: 1, 5, 6, 7, 9, 16
* <li>D-Gap computing: 1, 4, 1, 1, 2, 5 (so far - done by
* {@link DGapIntEncoder})
* <li>Encoding: 1,0,1,1,0,0,0,0 as the indicator, by 2 (4-2), 0 (2-2), 3 (5-2).
* <li>Binary encode: <u>0 | 0 | 0 | 0 | 1 | 1 | 0 | 1</u> 00000010 00000000
* 00000011 (indicator is <u>underlined</u>).<br>
* <b>NOTE:</b> the order of the values in the indicator is lsb ⇒ msb,
* which allows for more efficient decoding.
* </ul>
*
* @lucene.experimental
*/
public class EightFlagsIntEncoder extends ChunksIntEncoder {
/**
* Holds all combinations of <i>indicator</i> flags for fast encoding (saves
* time on bit manipulation at encode time)
*/
private static byte[] encodeTable = new byte[] { 0x1, 0x2, 0x4, 0x8, 0x10, 0x20, 0x40, (byte) 0x80 };
public EightFlagsIntEncoder() {
super(8);
}
@Override
public void encode(int data) throws IOException {
if (data == 1) {
indicator |= encodeTable[ordinal];
} else {
encodeQueue[encodeQueueSize++] = data - 2;
}
++ordinal;
// If 8 values were encoded thus far, 'flush' them including the indicator.
if ((ordinal & 0x7) == 0) {
encodeChunk();
}
}
@Override
public IntDecoder createMatchingDecoder() {
return new EightFlagsIntDecoder();
}
@Override
public String toString() {
return "EightFlags (" + encoder.toString() + ")";
}
}