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/*
* Copyright (C) 2011 The Guava Authors
*
* 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.google.common.hash;
import com.google.common.annotations.Beta;
import com.google.common.base.Preconditions;
import com.google.common.primitives.Ints;
import java.security.MessageDigest;
/**
* An immutable hash code of arbitrary bit length.
*
* @author Dimitris Andreou
* @since 11.0
*/
@Beta
public abstract class HashCode {
HashCode() {}
/**
* Returns the first four bytes of {@linkplain #asBytes() this hashcode's bytes}, converted to
* an {@code int} value in little-endian order.
*/
public abstract int asInt();
/**
* Returns the first eight bytes of {@linkplain #asBytes() this hashcode's bytes}, converted to
* a {@code long} value in little-endian order.
*
* @throws IllegalStateException if {@code bits() < 64}
*/
public abstract long asLong();
/**
* Returns the value of this hash code as a byte array. The caller may modify the byte array;
* changes to it will <i>not</i> be reflected in this {@code HashCode} object or any other arrays
* returned by this method.
*/
// TODO(user): consider ByteString here, when that is available
public abstract byte[] asBytes();
/**
* Copies bytes from this hash code into {@code dest}.
*
* @param dest the byte array into which the hash code will be written
* @param offset the start offset in the data
* @param maxLength the maximum number of bytes to write
* @return the number of bytes written to {@code dest}
* @throws IndexOutOfBoundsException if there is not enough room in {@code dest}
*/
public int writeBytesTo(byte[] dest, int offset, int maxLength) {
byte[] hash = asBytes();
maxLength = Ints.min(maxLength, hash.length);
Preconditions.checkPositionIndexes(offset, offset + maxLength, dest.length);
System.arraycopy(hash, 0, dest, offset, maxLength);
return maxLength;
}
/**
* Returns the number of bits in this hash code; a positive multiple of 32.
*/
public abstract int bits();
@Override public boolean equals(Object object) {
if (object instanceof HashCode) {
HashCode that = (HashCode) object;
// Undocumented: this is a non-short-circuiting equals(), in case this is a cryptographic
// hash code, in which case we don't want to leak timing information
return MessageDigest.isEqual(this.asBytes(), that.asBytes());
}
return false;
}
/**
* Returns a "Java hash code" for this {@code HashCode} instance; this is well-defined
* (so, for example, you can safely put {@code HashCode} instances into a {@code
* HashSet}) but is otherwise probably not what you want to use.
*/
@Override public int hashCode() {
/*
* As long as the hash function that produced this isn't of horrible quality, this
* won't be of horrible quality either.
*/
return asInt();
}
/**
* Returns a string containing each byte of {@link #asBytes}, in order, as a two-digit unsigned
* hexadecimal number in lower case.
*
* <p>Note that if the output is considered to be a single hexadecimal number, this hash code's
* bytes are the <i>big-endian</i> representation of that number. This may be surprising since
* everything else in the hashing API uniformly treats multibyte values as little-endian. But
* this format conveniently matches that of utilities such as the UNIX {@code md5sum} command.
*/
@Override public String toString() {
byte[] bytes = asBytes();
// TODO(user): Use c.g.common.base.ByteArrays once it is open sourced.
StringBuilder sb = new StringBuilder(2 * bytes.length);
for (byte b : bytes) {
sb.append(hexDigits[(b >> 4) & 0xf]).append(hexDigits[b & 0xf]);
}
return sb.toString();
}
private static final char[] hexDigits = "0123456789abcdef".toCharArray();
}
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