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      1 /*
      2  * Copyright (C) 2006 The Android Open Source Project
      3  *
      4  * Licensed under the Apache License, Version 2.0 (the "License");
      5  * you may not use this file except in compliance with the License.
      6  * You may obtain a copy of the License at
      7  *
      8  *      http://www.apache.org/licenses/LICENSE-2.0
      9  *
     10  * Unless required by applicable law or agreed to in writing, software
     11  * distributed under the License is distributed on an "AS IS" BASIS,
     12  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
     13  * See the License for the specific language governing permissions and
     14  * limitations under the License.
     15  */
     16 
     17 package com.android.internal.util;
     18 
     19 import java.lang.reflect.Array;
     20 import java.util.Collection;
     21 
     22 // XXX these should be changed to reflect the actual memory allocator we use.
     23 // it looks like right now objects want to be powers of 2 minus 8
     24 // and the array size eats another 4 bytes
     25 
     26 /**
     27  * ArrayUtils contains some methods that you can call to find out
     28  * the most efficient increments by which to grow arrays.
     29  */
     30 public class ArrayUtils
     31 {
     32     private static Object[] EMPTY = new Object[0];
     33     private static final int CACHE_SIZE = 73;
     34     private static Object[] sCache = new Object[CACHE_SIZE];
     35 
     36     private ArrayUtils() { /* cannot be instantiated */ }
     37 
     38     public static int idealByteArraySize(int need) {
     39         for (int i = 4; i < 32; i++)
     40             if (need <= (1 << i) - 12)
     41                 return (1 << i) - 12;
     42 
     43         return need;
     44     }
     45 
     46     public static int idealBooleanArraySize(int need) {
     47         return idealByteArraySize(need);
     48     }
     49 
     50     public static int idealShortArraySize(int need) {
     51         return idealByteArraySize(need * 2) / 2;
     52     }
     53 
     54     public static int idealCharArraySize(int need) {
     55         return idealByteArraySize(need * 2) / 2;
     56     }
     57 
     58     public static int idealIntArraySize(int need) {
     59         return idealByteArraySize(need * 4) / 4;
     60     }
     61 
     62     public static int idealFloatArraySize(int need) {
     63         return idealByteArraySize(need * 4) / 4;
     64     }
     65 
     66     public static int idealObjectArraySize(int need) {
     67         return idealByteArraySize(need * 4) / 4;
     68     }
     69 
     70     public static int idealLongArraySize(int need) {
     71         return idealByteArraySize(need * 8) / 8;
     72     }
     73 
     74     /**
     75      * Checks if the beginnings of two byte arrays are equal.
     76      *
     77      * @param array1 the first byte array
     78      * @param array2 the second byte array
     79      * @param length the number of bytes to check
     80      * @return true if they're equal, false otherwise
     81      */
     82     public static boolean equals(byte[] array1, byte[] array2, int length) {
     83         if (array1 == array2) {
     84             return true;
     85         }
     86         if (array1 == null || array2 == null || array1.length < length || array2.length < length) {
     87             return false;
     88         }
     89         for (int i = 0; i < length; i++) {
     90             if (array1[i] != array2[i]) {
     91                 return false;
     92             }
     93         }
     94         return true;
     95     }
     96 
     97     /**
     98      * Returns an empty array of the specified type.  The intent is that
     99      * it will return the same empty array every time to avoid reallocation,
    100      * although this is not guaranteed.
    101      */
    102     public static <T> T[] emptyArray(Class<T> kind) {
    103         if (kind == Object.class) {
    104             return (T[]) EMPTY;
    105         }
    106 
    107         int bucket = ((System.identityHashCode(kind) / 8) & 0x7FFFFFFF) % CACHE_SIZE;
    108         Object cache = sCache[bucket];
    109 
    110         if (cache == null || cache.getClass().getComponentType() != kind) {
    111             cache = Array.newInstance(kind, 0);
    112             sCache[bucket] = cache;
    113 
    114             // Log.e("cache", "new empty " + kind.getName() + " at " + bucket);
    115         }
    116 
    117         return (T[]) cache;
    118     }
    119 
    120     /**
    121      * Checks that value is present as at least one of the elements of the array.
    122      * @param array the array to check in
    123      * @param value the value to check for
    124      * @return true if the value is present in the array
    125      */
    126     public static <T> boolean contains(T[] array, T value) {
    127         for (T element : array) {
    128             if (element == null) {
    129                 if (value == null) return true;
    130             } else {
    131                 if (value != null && element.equals(value)) return true;
    132             }
    133         }
    134         return false;
    135     }
    136 
    137     public static boolean contains(int[] array, int value) {
    138         for (int element : array) {
    139             if (element == value) {
    140                 return true;
    141             }
    142         }
    143         return false;
    144     }
    145 }
    146