/*
* Copyright (c) [2016] [ <ether.camp> ]
* This file is part of the ethereumJ library.
*
* The ethereumJ library is free software: you can redistribute it and/or modify
* it under the terms of the GNU Lesser General Public License as published by
* the Free Software Foundation, either version 3 of the License, or
* (at your option) any later version.
*
* The ethereumJ library is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU Lesser General Public License for more details.
*
* You should have received a copy of the GNU Lesser General Public License
* along with the ethereumJ library. If not, see <http://www.gnu.org/licenses/>.
*/
/**
* 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.
*/
package org.ethereum.util;
import com.google.common.primitives.UnsignedBytes;
/**
* Utility code to do optimized byte-array comparison.
* This is borrowed and slightly modified from Guava's {@link UnsignedBytes}
* class to be able to compare arrays that start at non-zero offsets.
*/
@SuppressWarnings("restriction")
public abstract class FastByteComparisons {
public static boolean equal(byte[] b1, byte[] b2) {
return b1.length == b2.length && compareTo(b1, 0, b1.length, b2, 0, b2.length) == 0;
}
/**
* Lexicographically compare two byte arrays.
*
* @param b1 buffer1
* @param s1 offset1
* @param l1 length1
* @param b2 buffer2
* @param s2 offset2
* @param l2 length2
* @return int
*/
public static int compareTo(byte[] b1, int s1, int l1, byte[] b2, int s2, int l2) {
return LexicographicalComparerHolder.BEST_COMPARER.compareTo(
b1, s1, l1, b2, s2, l2);
}
private interface Comparer<T> {
int compareTo(T buffer1, int offset1, int length1,
T buffer2, int offset2, int length2);
}
private static Comparer<byte[]> lexicographicalComparerJavaImpl() {
return LexicographicalComparerHolder.PureJavaComparer.INSTANCE;
}
/**
*
* <p>Uses reflection to gracefully fall back to the Java implementation if
* {@code Unsafe} isn't available.
*/
private static class LexicographicalComparerHolder {
static final String UNSAFE_COMPARER_NAME =
LexicographicalComparerHolder.class.getName() + "$UnsafeComparer";
static final Comparer<byte[]> BEST_COMPARER = getBestComparer();
/**
* Returns the Unsafe-using Comparer, or falls back to the pure-Java
* implementation if unable to do so.
*/
static Comparer<byte[]> getBestComparer() {
try {
Class<?> theClass = Class.forName(UNSAFE_COMPARER_NAME);
// yes, UnsafeComparer does implement Comparer<byte[]>
@SuppressWarnings("unchecked")
Comparer<byte[]> comparer =
(Comparer<byte[]>) theClass.getEnumConstants()[0];
return comparer;
} catch (Throwable t) { // ensure we really catch *everything*
return lexicographicalComparerJavaImpl();
}
}
private enum PureJavaComparer implements Comparer<byte[]> {
INSTANCE;
@Override
public int compareTo(byte[] buffer1, int offset1, int length1,
byte[] buffer2, int offset2, int length2) {
// Short circuit equal case
if (buffer1 == buffer2 &&
offset1 == offset2 &&
length1 == length2) {
return 0;
}
int end1 = offset1 + length1;
int end2 = offset2 + length2;
for (int i = offset1, j = offset2; i < end1 && j < end2; i++, j++) {
int a = (buffer1[i] & 0xff);
int b = (buffer2[j] & 0xff);
if (a != b) {
return a - b;
}
}
return length1 - length2;
}
}
}
}