/*
* Copyright 2016 Naver Corp.
*
* Licensed 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 com.navercorp.pinpoint.common.server.bo.codec.stat.header;
import java.util.BitSet;
/**
* Bit-counting implementation of {@link AgentStatHeaderEncoder} that encodes
* each code by setting the number of bits equal to it followed by a 0.
*
* <p>For example, codes {1, 0, 2} will be encoded as 100110.
*
* <p>This implementation is best suited for very small code values (ideally
* those that take less than a few bits to encode). It is very inefficient for
* values larger than this, and other implementations should be used in place
* of this.
*
* @author HyunGil Jeong
* @see BitCountingHeaderDecoder
*/
public class BitCountingHeaderEncoder implements AgentStatHeaderEncoder {
private static final int NUM_BITS_PER_BYTE = 8;
private final BitSet headerBitSet = new BitSet();
private int position = 0;
@Override
public void addCode(int code) {
if (code < 0) {
throw new IllegalArgumentException("code must be positive");
}
int fromIndex = this.position;
int toIndex = this.position + code;
this.headerBitSet.set(fromIndex, toIndex);
this.position = toIndex + 1;
}
@Override
public byte[] getHeader() {
if (position == 0) {
return new byte[0];
}
// strictly follows JDK 7's BitSet.toByteArray()
int len = (headerBitSet.length() + (NUM_BITS_PER_BYTE - 1)) / NUM_BITS_PER_BYTE;
byte[] header = new byte[len];
for (int i = 0; i < len * NUM_BITS_PER_BYTE; ++i) {
int index = i / NUM_BITS_PER_BYTE;
int bitMask = (headerBitSet.get(i) ? 1 : 0) << (i % NUM_BITS_PER_BYTE);
header[index] |= bitMask;
}
return header;
// use below when using JDK 7+
// return this.headerBitSet.toByteArray();
}
}