/*
* Copyright (C) 2014 The Android Open Source Project
*
* 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 android.hardware.camera2.utils;
/**
* Provide hashing functions using the Modified Bernstein hash
*/
public final class HashCodeHelpers {
/**
* Hash every element uniformly using the Modified Bernstein hash.
*
* <p>Useful to implement a {@link Object#hashCode} for uniformly distributed data.</p>
*
* @param array a non-{@code null} array of integers
*
* @return the numeric hash code
*/
public static int hashCode(int... array) {
if (array == null) {
return 0;
}
/*
* Note that we use 31 here instead of 33 since it's preferred in Effective Java
* and used elsewhere in the runtime (e.g. Arrays#hashCode)
*
* That being said 33 and 31 are nearly identical in terms of their usefulness
* according to http://svn.apache.org/repos/asf/apr/apr/trunk/tables/apr_hash.c
*/
int h = 1;
for (int x : array) {
// Strength reduction; in case the compiler has illusions about divisions being faster
h = ((h << 5) - h) ^ x; // (h * 31) XOR x
}
return h;
}
/**
* Hash every element uniformly using the Modified Bernstein hash.
*
* <p>Useful to implement a {@link Object#hashCode} for uniformly distributed data.</p>
*
* @param array a non-{@code null} array of floats
*
* @return the numeric hash code
*/
public static int hashCode(float... array) {
if (array == null) {
return 0;
}
int h = 1;
for (float f : array) {
int x = Float.floatToIntBits(f);
h = ((h << 5) - h) ^ x; // (h * 31) XOR x
}
return h;
}
/**
* Hash every element uniformly using the Modified Bernstein hash.
*
* <p>Useful to implement a {@link Object#hashCode} for uniformly distributed data.</p>
*
* @param array a non-{@code null} array of objects
*
* @return the numeric hash code
*/
public static <T> int hashCodeGeneric(T... array) {
if (array == null) {
return 0;
}
int h = 1;
for (T o : array) {
int x = (o == null) ? 0 : o.hashCode();
h = ((h << 5) - h) ^ x; // (h * 31) XOR x
}
return h;
}
}