/*
* 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 AgentStatHeaderDecoder} that decodes
* each code by counting the number of set bits until the next unset bit.
* If all bits are used up, the subsequent {@link #getCode()} invocations will
* simply return 0.
*
* <p>For example, given a header of 100110, {@link #getCode()} will return 1,
* 0, 2, and 0s afterwards.</p>
*
* @author HyunGil Jeong
* @see BitCountingHeaderDecoder
*/
public class BitCountingHeaderDecoder implements AgentStatHeaderDecoder {
private static final int NUM_BITS_PER_BYTE = 8;
private final BitSet headerBitSet;
private int position = 0;
public BitCountingHeaderDecoder(byte[] header) {
headerBitSet = new BitSet();
// strictly follows JDK 7's BitSet.valueOf(byte[])
for (int i = 0; i < header.length * NUM_BITS_PER_BYTE; i++) {
byte currentBits = header[i / NUM_BITS_PER_BYTE];
int bitMask = 1 << (i % NUM_BITS_PER_BYTE);
if ((currentBits & bitMask) > 0) {
headerBitSet.set(i);
}
}
// use below when using JDK 7+
// this.headerBitSet = BitSet.valueOf(header);
}
@Override
public int getCode() {
int fromIndex = this.position;
int toIndex = this.headerBitSet.nextClearBit(this.position);
int numBitsSet = this.headerBitSet.get(fromIndex, toIndex).cardinality();
this.position = toIndex + 1;
return numBitsSet;
}
}