io.netty.buffer.search.KmpSearchProcessorFactory Maven / Gradle / Ivy
/*
* Copyright 2020 The Netty Project
*
* The Netty Project 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 io.netty.buffer.search;
import io.netty.util.internal.PlatformDependent;
/**
* Implements
* Knuth-Morris-Pratt
* string search algorithm.
* Use static {@link AbstractSearchProcessorFactory#newKmpSearchProcessorFactory}
* to create an instance of this factory.
* Use {@link KmpSearchProcessorFactory#newSearchProcessor} to get an instance of {@link io.netty.util.ByteProcessor}
* implementation for performing the actual search.
* @see AbstractSearchProcessorFactory
*/
public class KmpSearchProcessorFactory extends AbstractSearchProcessorFactory {
private final int[] jumpTable;
private final byte[] needle;
public static class Processor implements SearchProcessor {
private final byte[] needle;
private final int[] jumpTable;
private long currentPosition;
Processor(byte[] needle, int[] jumpTable) {
this.needle = needle;
this.jumpTable = jumpTable;
}
@Override
public boolean process(byte value) {
while (currentPosition > 0 && PlatformDependent.getByte(needle, currentPosition) != value) {
currentPosition = PlatformDependent.getInt(jumpTable, currentPosition);
}
if (PlatformDependent.getByte(needle, currentPosition) == value) {
currentPosition++;
}
if (currentPosition == needle.length) {
currentPosition = PlatformDependent.getInt(jumpTable, currentPosition);
return false;
}
return true;
}
@Override
public void reset() {
currentPosition = 0;
}
}
KmpSearchProcessorFactory(byte[] needle) {
this.needle = needle.clone();
this.jumpTable = new int[needle.length + 1];
int j = 0;
for (int i = 1; i < needle.length; i++) {
while (j > 0 && needle[j] != needle[i]) {
j = jumpTable[j];
}
if (needle[j] == needle[i]) {
j++;
}
jumpTable[i + 1] = j;
}
}
/**
* Returns a new {@link Processor}.
*/
@Override
public Processor newSearchProcessor() {
return new Processor(needle, jumpTable);
}
}