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      1 /*
      2  * Copyright (C) 2017 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 
     18 package com.android.internal.util;
     19 
     20 import android.annotation.Nullable;
     21 import android.text.TextUtils;
     22 
     23 import java.nio.ByteBuffer;
     24 import java.util.Arrays;
     25 import java.util.Objects;
     26 import java.util.UUID;
     27 import java.util.function.IntFunction;
     28 
     29 /**
     30  * A utility class for handling unsigned integers and unsigned arithmetics, as well as syntactic
     31  * sugar methods for ByteBuffer. Useful for networking and packet manipulations.
     32  * {@hide}
     33  */
     34 public final class BitUtils {
     35     private BitUtils() {}
     36 
     37     public static boolean maskedEquals(long a, long b, long mask) {
     38         return (a & mask) == (b & mask);
     39     }
     40 
     41     public static boolean maskedEquals(byte a, byte b, byte mask) {
     42         return (a & mask) == (b & mask);
     43     }
     44 
     45     public static boolean maskedEquals(byte[] a, byte[] b, @Nullable byte[] mask) {
     46         if (a == null || b == null) return a == b;
     47         Preconditions.checkArgument(a.length == b.length, "Inputs must be of same size");
     48         if (mask == null) return Arrays.equals(a, b);
     49         Preconditions.checkArgument(a.length == mask.length, "Mask must be of same size as inputs");
     50         for (int i = 0; i < mask.length; i++) {
     51             if (!maskedEquals(a[i], b[i], mask[i])) return false;
     52         }
     53         return true;
     54     }
     55 
     56     public static boolean maskedEquals(UUID a, UUID b, @Nullable UUID mask) {
     57         if (mask == null) {
     58             return Objects.equals(a, b);
     59         }
     60         return maskedEquals(a.getLeastSignificantBits(), b.getLeastSignificantBits(),
     61                     mask.getLeastSignificantBits())
     62                 && maskedEquals(a.getMostSignificantBits(), b.getMostSignificantBits(),
     63                     mask.getMostSignificantBits());
     64     }
     65 
     66     public static int[] unpackBits(long val) {
     67         int size = Long.bitCount(val);
     68         int[] result = new int[size];
     69         int index = 0;
     70         int bitPos = 0;
     71         while (val > 0) {
     72             if ((val & 1) == 1) result[index++] = bitPos;
     73             val = val >> 1;
     74             bitPos++;
     75         }
     76         return result;
     77     }
     78 
     79     public static long packBits(int[] bits) {
     80         long packed = 0;
     81         for (int b : bits) {
     82             packed |= (1 << b);
     83         }
     84         return packed;
     85     }
     86 
     87     public static int uint8(byte b) {
     88         return b & 0xff;
     89     }
     90 
     91     public static int uint16(short s) {
     92         return s & 0xffff;
     93     }
     94 
     95     public static int uint16(byte hi, byte lo) {
     96         return ((hi & 0xff) << 8) | (lo & 0xff);
     97     }
     98 
     99     public static long uint32(int i) {
    100         return i & 0xffffffffL;
    101     }
    102 
    103     public static int bytesToBEInt(byte[] bytes) {
    104         return (uint8(bytes[0]) << 24)
    105                 + (uint8(bytes[1]) << 16)
    106                 + (uint8(bytes[2]) << 8)
    107                 + (uint8(bytes[3]));
    108     }
    109 
    110     public static int bytesToLEInt(byte[] bytes) {
    111         return Integer.reverseBytes(bytesToBEInt(bytes));
    112     }
    113 
    114     public static int getUint8(ByteBuffer buffer, int position) {
    115         return uint8(buffer.get(position));
    116     }
    117 
    118     public static int getUint16(ByteBuffer buffer, int position) {
    119         return uint16(buffer.getShort(position));
    120     }
    121 
    122     public static long getUint32(ByteBuffer buffer, int position) {
    123         return uint32(buffer.getInt(position));
    124     }
    125 
    126     public static void put(ByteBuffer buffer, int position, byte[] bytes) {
    127         final int original = buffer.position();
    128         buffer.position(position);
    129         buffer.put(bytes);
    130         buffer.position(original);
    131     }
    132 
    133     public static boolean isBitSet(long flags, int bitIndex) {
    134         return (flags & bitAt(bitIndex)) != 0;
    135     }
    136 
    137     public static long bitAt(int bitIndex) {
    138         return 1L << bitIndex;
    139     }
    140 
    141     public static String flagsToString(int flags, IntFunction<String> getFlagName) {
    142         StringBuilder builder = new StringBuilder();
    143         int count = 0;
    144         while (flags != 0) {
    145             final int flag = 1 << Integer.numberOfTrailingZeros(flags);
    146             flags &= ~flag;
    147             if (count > 0) builder.append(", ");
    148             builder.append(getFlagName.apply(flag));
    149             count++;
    150         }
    151         TextUtils.wrap(builder, "[", "]");
    152         return builder.toString();
    153     }
    154 }
    155