001/* 002 * Copyright (C) 2013 The Guava Authors 003 * 004 * Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except 005 * in compliance with the License. You may obtain a copy of the License at 006 * 007 * http://www.apache.org/licenses/LICENSE-2.0 008 * 009 * Unless required by applicable law or agreed to in writing, software distributed under the License 010 * is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express 011 * or implied. See the License for the specific language governing permissions and limitations under 012 * the License. 013 */ 014 015package com.google.common.base; 016 017import static com.google.common.base.Preconditions.checkPositionIndexes; 018import static java.lang.Character.MAX_SURROGATE; 019import static java.lang.Character.MIN_SURROGATE; 020 021import com.google.common.annotations.Beta; 022import com.google.common.annotations.GwtCompatible; 023 024/** 025 * Low-level, high-performance utility methods related to the {@linkplain Charsets#UTF_8 UTF-8} 026 * character encoding. UTF-8 is defined in section D92 of 027 * <a href="http://www.unicode.org/versions/Unicode6.2.0/ch03.pdf">The Unicode Standard Core 028 * Specification, Chapter 3</a>. 029 * 030 * <p>The variant of UTF-8 implemented by this class is the restricted definition of UTF-8 031 * introduced in Unicode 3.1. One implication of this is that it rejects 032 * <a href="http://www.unicode.org/versions/corrigendum1.html">"non-shortest form"</a> byte 033 * sequences, even though the JDK decoder may accept them. 034 * 035 * @author Martin Buchholz 036 * @author Clément Roux 037 * @since 16.0 038 */ 039@Beta 040@GwtCompatible(emulated = true) 041public final class Utf8 { 042 /** 043 * Returns the number of bytes in the UTF-8-encoded form of {@code sequence}. For a string, this 044 * method is equivalent to {@code string.getBytes(UTF_8).length}, but is more efficient in both 045 * time and space. 046 * 047 * @throws IllegalArgumentException if {@code sequence} contains ill-formed UTF-16 (unpaired 048 * surrogates) 049 */ 050 public static int encodedLength(CharSequence sequence) { 051 // Warning to maintainers: this implementation is highly optimized. 052 int utf16Length = sequence.length(); 053 int utf8Length = utf16Length; 054 int i = 0; 055 056 // This loop optimizes for pure ASCII. 057 while (i < utf16Length && sequence.charAt(i) < 0x80) { 058 i++; 059 } 060 061 // This loop optimizes for chars less than 0x800. 062 for (; i < utf16Length; i++) { 063 char c = sequence.charAt(i); 064 if (c < 0x800) { 065 utf8Length += ((0x7f - c) >>> 31); // branch free! 066 } else { 067 utf8Length += encodedLengthGeneral(sequence, i); 068 break; 069 } 070 } 071 072 if (utf8Length < utf16Length) { 073 // Necessary and sufficient condition for overflow because of maximum 3x expansion 074 throw new IllegalArgumentException( 075 "UTF-8 length does not fit in int: " + (utf8Length + (1L << 32))); 076 } 077 return utf8Length; 078 } 079 080 private static int encodedLengthGeneral(CharSequence sequence, int start) { 081 int utf16Length = sequence.length(); 082 int utf8Length = 0; 083 for (int i = start; i < utf16Length; i++) { 084 char c = sequence.charAt(i); 085 if (c < 0x800) { 086 utf8Length += (0x7f - c) >>> 31; // branch free! 087 } else { 088 utf8Length += 2; 089 // jdk7+: if (Character.isSurrogate(c)) { 090 if (MIN_SURROGATE <= c && c <= MAX_SURROGATE) { 091 // Check that we have a well-formed surrogate pair. 092 if (Character.codePointAt(sequence, i) == c) { 093 throw new IllegalArgumentException(unpairedSurrogateMsg(i)); 094 } 095 i++; 096 } 097 } 098 } 099 return utf8Length; 100 } 101 102 /** 103 * Returns {@code true} if {@code bytes} is a <i>well-formed</i> UTF-8 byte sequence according to 104 * Unicode 6.0. Note that this is a stronger criterion than simply whether the bytes can be 105 * decoded. For example, some versions of the JDK decoder will accept "non-shortest form" byte 106 * sequences, but encoding never reproduces these. Such byte sequences are <i>not</i> considered 107 * well-formed. 108 * 109 * <p>This method returns {@code true} if and only if {@code Arrays.equals(bytes, new 110 * String(bytes, UTF_8).getBytes(UTF_8))} does, but is more efficient in both time and space. 111 */ 112 public static boolean isWellFormed(byte[] bytes) { 113 return isWellFormed(bytes, 0, bytes.length); 114 } 115 116 /** 117 * Returns whether the given byte array slice is a well-formed UTF-8 byte sequence, as defined by 118 * {@link #isWellFormed(byte[])}. Note that this can be false even when {@code 119 * isWellFormed(bytes)} is true. 120 * 121 * @param bytes the input buffer 122 * @param off the offset in the buffer of the first byte to read 123 * @param len the number of bytes to read from the buffer 124 */ 125 public static boolean isWellFormed(byte[] bytes, int off, int len) { 126 int end = off + len; 127 checkPositionIndexes(off, end, bytes.length); 128 // Look for the first non-ASCII character. 129 for (int i = off; i < end; i++) { 130 if (bytes[i] < 0) { 131 return isWellFormedSlowPath(bytes, i, end); 132 } 133 } 134 return true; 135 } 136 137 private static boolean isWellFormedSlowPath(byte[] bytes, int off, int end) { 138 int index = off; 139 while (true) { 140 int byte1; 141 142 // Optimize for interior runs of ASCII bytes. 143 do { 144 if (index >= end) { 145 return true; 146 } 147 } while ((byte1 = bytes[index++]) >= 0); 148 149 if (byte1 < (byte) 0xE0) { 150 // Two-byte form. 151 if (index == end) { 152 return false; 153 } 154 // Simultaneously check for illegal trailing-byte in leading position 155 // and overlong 2-byte form. 156 if (byte1 < (byte) 0xC2 || bytes[index++] > (byte) 0xBF) { 157 return false; 158 } 159 } else if (byte1 < (byte) 0xF0) { 160 // Three-byte form. 161 if (index + 1 >= end) { 162 return false; 163 } 164 int byte2 = bytes[index++]; 165 if (byte2 > (byte) 0xBF 166 // Overlong? 5 most significant bits must not all be zero. 167 || (byte1 == (byte) 0xE0 && byte2 < (byte) 0xA0) 168 // Check for illegal surrogate codepoints. 169 || (byte1 == (byte) 0xED && (byte) 0xA0 <= byte2) 170 // Third byte trailing-byte test. 171 || bytes[index++] > (byte) 0xBF) { 172 return false; 173 } 174 } else { 175 // Four-byte form. 176 if (index + 2 >= end) { 177 return false; 178 } 179 int byte2 = bytes[index++]; 180 if (byte2 > (byte) 0xBF 181 // Check that 1 <= plane <= 16. Tricky optimized form of: 182 // if (byte1 > (byte) 0xF4 183 // || byte1 == (byte) 0xF0 && byte2 < (byte) 0x90 184 // || byte1 == (byte) 0xF4 && byte2 > (byte) 0x8F) 185 || (((byte1 << 28) + (byte2 - (byte) 0x90)) >> 30) != 0 186 // Third byte trailing-byte test 187 || bytes[index++] > (byte) 0xBF 188 // Fourth byte trailing-byte test 189 || bytes[index++] > (byte) 0xBF) { 190 return false; 191 } 192 } 193 } 194 } 195 196 private static String unpairedSurrogateMsg(int i) { 197 return "Unpaired surrogate at index " + i; 198 } 199 200 private Utf8() {} 201}