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 {@link ByteBuffer}. Useful for networking and packet manipulations.
32  * {@hide}
33  */
34 public final class BitUtils {
BitUtils()35     private BitUtils() {}
36 
maskedEquals(long a, long b, long mask)37     public static boolean maskedEquals(long a, long b, long mask) {
38         return (a & mask) == (b & mask);
39     }
40 
maskedEquals(byte a, byte b, byte mask)41     public static boolean maskedEquals(byte a, byte b, byte mask) {
42         return (a & mask) == (b & mask);
43     }
44 
maskedEquals(byte[] a, byte[] b, @Nullable byte[] mask)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 
maskedEquals(UUID a, UUID b, @Nullable UUID mask)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 
unpackBits(long val)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 
packBits(int[] bits)79     public static long packBits(int[] bits) {
80         long packed = 0;
81         for (int b : bits) {
82             packed |= (1L << b);
83         }
84         return packed;
85     }
86 
uint8(byte b)87     public static int uint8(byte b) {
88         return b & 0xff;
89     }
90 
uint16(short s)91     public static int uint16(short s) {
92         return s & 0xffff;
93     }
94 
uint16(byte hi, byte lo)95     public static int uint16(byte hi, byte lo) {
96         return ((hi & 0xff) << 8) | (lo & 0xff);
97     }
98 
uint32(int i)99     public static long uint32(int i) {
100         return i & 0xffffffffL;
101     }
102 
bytesToBEInt(byte[] bytes)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 
bytesToLEInt(byte[] bytes)110     public static int bytesToLEInt(byte[] bytes) {
111         return Integer.reverseBytes(bytesToBEInt(bytes));
112     }
113 
getUint8(ByteBuffer buffer, int position)114     public static int getUint8(ByteBuffer buffer, int position) {
115         return uint8(buffer.get(position));
116     }
117 
getUint16(ByteBuffer buffer, int position)118     public static int getUint16(ByteBuffer buffer, int position) {
119         return uint16(buffer.getShort(position));
120     }
121 
getUint32(ByteBuffer buffer, int position)122     public static long getUint32(ByteBuffer buffer, int position) {
123         return uint32(buffer.getInt(position));
124     }
125 
put(ByteBuffer buffer, int position, byte[] bytes)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 
isBitSet(long flags, int bitIndex)133     public static boolean isBitSet(long flags, int bitIndex) {
134         return (flags & bitAt(bitIndex)) != 0;
135     }
136 
bitAt(int bitIndex)137     public static long bitAt(int bitIndex) {
138         return 1L << bitIndex;
139     }
140 
flagsToString(int flags, IntFunction<String> getFlagName)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     /**
156      * Converts long to byte array
157      */
toBytes(long l)158     public static byte[] toBytes(long l) {
159         return ByteBuffer.allocate(8).putLong(l).array();
160     }
161 
162     /**
163      * 0b01000 -> 0b01111
164      */
flagsUpTo(int lastFlag)165     public static int flagsUpTo(int lastFlag) {
166         return lastFlag <= 0 ? 0 : lastFlag | flagsUpTo(lastFlag >> 1);
167     }
168 
169     /**
170      * 0b00010, 0b01000 -> 0b01110
171      */
flagsWithin(int firstFlag, int lastFlag)172     public static int flagsWithin(int firstFlag, int lastFlag) {
173         return (flagsUpTo(lastFlag) & ~flagsUpTo(firstFlag)) | firstFlag;
174     }
175 }
176