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.
*/
/**
* An {@link IntEncoder} which implements variable length encoding. A number is
* encoded as follows:
* <ul>
* <li>If it is less than 127 and non-negative, i.e. uses only 7 bits, it is
* encoded as a single byte: 0bbbbbbb.
* <li>If it occupies more than 7 bits, it is represented as a series of bytes,
* each byte carrying 7 bits. All but the last byte have the MSB set, the last
* one has it unset.
* </ul>
* Example:
* <ol>
* <li>n = 117 = 01110101: This has less than 8 significant bits, therefore is
* encoded as 01110101 = 0x75.
* <li>n = 100000 = (binary) 11000011010100000. This has 17 significant bits,
* thus needs three Vint8 bytes. Pad it to a multiple of 7 bits, then split it
* into chunks of 7 and add an MSB, 0 for the last byte, 1 for the others:
* 1|0000110 1|0001101 0|0100000 = 0x86 0x8D 0x20.
* </ol>
* <b>NOTE:</b> although this encoder is not limited to values ≥ 0, it is not
* recommended for use with negative values, as their encoding will result in 5
* bytes written to the output stream, rather than 4. For such values, either
* use {@link SimpleIntEncoder} or write your own version of variable length
* encoding, which can better handle negative values.
*
* @lucene.experimental
*/
public class VInt8IntEncoder extends IntEncoder {
@Override
public void encode(int value) throws IOException {
if ((value & ~0x7F) == 0) {
out.write(value);
} else if ((value & ~0x3FFF) == 0) {
out.write(0x80 | (value >> 7));
out.write(0x7F & value);
} else if ((value & ~0x1FFFFF) == 0) {
out.write(0x80 | (value >> 14));
out.write(0x80 | (value >> 7));
out.write(0x7F & value);
} else if ((value & ~0xFFFFFFF) == 0) {
out.write(0x80 | (value >> 21));
out.write(0x80 | (value >> 14));
out.write(0x80 | (value >> 7));
out.write(0x7F & value);
} else {
out.write(0x80 | (value >> 28));
out.write(0x80 | (value >> 21));
out.write(0x80 | (value >> 14));
out.write(0x80 | (value >> 7));
out.write(0x7F & value);
}
}
@Override
public IntDecoder createMatchingDecoder() {
return new VInt8IntDecoder();
}
@Override
public String toString() {
return "VInt8";
}
}