org.nd4j.linalg.util.HashUtil Maven / Gradle / Ivy
/*******************************************************************************
* Copyright (c) 2015-2018 Skymind, Inc.
*
* This program and the accompanying materials are made available under the
* terms of the Apache License, Version 2.0 which is available at
* https://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.
*
* SPDX-License-Identifier: Apache-2.0
******************************************************************************/
package org.nd4j.linalg.util;
import lombok.NonNull;
/**
* Stronger 64-bit hash function helper, as described here: http://www.javamex.com/tutorials/collections/strong_hash_code_implementation.shtml
*
* @author [email protected]
*/
public class HashUtil {
private static final long[] byteTable = createLookupTable();
private static final long HSTART = 0xBB40E64DA205B064L;
private static final long HMULT = 7664345821815920749L;
private static long[] createLookupTable() {
long[] byteTable = new long[256];
long h = 0x544B2FBACAAF1684L;
for (int i = 0; i < 256; i++) {
for (int j = 0; j < 31; j++) {
h = (h >>> 7) ^ h;
h = (h << 11) ^ h;
h = (h >>> 10) ^ h;
}
byteTable[i] = h;
}
return byteTable;
}
/**
* This method returns long hash for a given bytes array
*
* @param data
* @return
*/
public static long getLongHash(@NonNull byte[] data) {
long h = HSTART;
final long hmult = HMULT;
final long[] ht = byteTable;
for (int len = data.length, i = 0; i < len; i++) {
h = (h * hmult) ^ ht[data[i] & 0xff];
}
return h;
}
/**
* This method returns long hash for a given string
*
* @param string
* @return
*/
public static long getLongHash(@NonNull String string) {
long h = HSTART;
final long hmult = HMULT;
final long[] ht = byteTable;
final int len = string.length();
for (int i = 0; i < len; i++) {
char ch = string.charAt(i);
h = (h * hmult) ^ ht[ch & 0xff];
h = (h * hmult) ^ ht[(ch >>> 8) & 0xff];
}
return h;
}
}