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; 018 019import com.google.common.annotations.Beta; 020import com.google.common.annotations.GwtCompatible; 021 022/** 023 * Low-level, high-performance utility methods related to the {@linkplain Charsets#UTF_8 UTF-8} 024 * character encoding. UTF-8 is defined in section D92 of 025 * <a href="http://www.unicode.org/versions/Unicode6.2.0/ch03.pdf">The Unicode Standard Core 026 * Specification, Chapter 3</a>. 027 * 028 * <p>The variant of UTF-8 implemented by this class is the restricted definition of UTF-8 029 * introduced in Unicode 3.1. One implication of this is that it rejects 030 * <a href="http://www.unicode.org/versions/corrigendum1.html">"non-shortest form"</a> byte 031 * sequences, even though the JDK decoder may accept them. 032 * 033 * @author Martin Buchholz 034 * @author Clément Roux 035 * @since 16.0 036 */ 037@Beta 038@GwtCompatible 039public final class Utf8 { 040 /** 041 * Returns the number of bytes in the UTF-8-encoded form of {@code sequence}. For a string, 042 * this method is equivalent to {@code string.getBytes(UTF_8).length}, but is more efficient in 043 * both time and space. 044 * 045 * @throws IllegalArgumentException if {@code sequence} contains ill-formed UTF-16 (unpaired 046 * surrogates) 047 */ 048 public static int encodedLength(CharSequence sequence) { 049 // Warning to maintainers: this implementation is highly optimized. 050 int utf16Length = sequence.length(); 051 int utf8Length = utf16Length; 052 int i = 0; 053 054 // This loop optimizes for pure ASCII. 055 while (i < utf16Length && sequence.charAt(i) < 0x80) { 056 i++; 057 } 058 059 // This loop optimizes for chars less than 0x800. 060 for (; i < utf16Length; i++) { 061 char c = sequence.charAt(i); 062 if (c < 0x800) { 063 utf8Length += ((0x7f - c) >>> 31); // branch free! 064 } else { 065 utf8Length += encodedLengthGeneral(sequence, i); 066 break; 067 } 068 } 069 070 if (utf8Length < utf16Length) { 071 // Necessary and sufficient condition for overflow because of maximum 3x expansion 072 throw new IllegalArgumentException("UTF-8 length does not fit in int: " 073 + (utf8Length + (1L << 32))); 074 } 075 return utf8Length; 076 } 077 078 private static int encodedLengthGeneral(CharSequence sequence, int start) { 079 int utf16Length = sequence.length(); 080 int utf8Length = 0; 081 for (int i = start; i < utf16Length; i++) { 082 char c = sequence.charAt(i); 083 if (c < 0x800) { 084 utf8Length += (0x7f - c) >>> 31; // branch free! 085 } else { 086 utf8Length += 2; 087 // jdk7+: if (Character.isSurrogate(c)) { 088 if (Character.MIN_SURROGATE <= c && c <= Character.MAX_SURROGATE) { 089 // Check that we have a well-formed surrogate pair. 090 int cp = Character.codePointAt(sequence, i); 091 if (cp < Character.MIN_SUPPLEMENTARY_CODE_POINT) { 092 throw new IllegalArgumentException("Unpaired surrogate at index " + i); 093 } 094 i++; 095 } 096 } 097 } 098 return utf8Length; 099 } 100 101 /** 102 * Returns {@code true} if {@code bytes} is a <i>well-formed</i> UTF-8 byte sequence according to 103 * Unicode 6.0. Note that this is a stronger criterion than simply whether the bytes can be 104 * decoded. For example, some versions of the JDK decoder will accept "non-shortest form" byte 105 * sequences, but encoding never reproduces these. Such byte sequences are <i>not</i> considered 106 * well-formed. 107 * 108 * <p>This method returns {@code true} if and only if {@code Arrays.equals(bytes, new 109 * String(bytes, UTF_8).getBytes(UTF_8))} does, but is more efficient in both time and space. 110 */ 111 public static boolean isWellFormed(byte[] bytes) { 112 return isWellFormed(bytes, 0, bytes.length); 113 } 114 115 /** 116 * Returns whether the given byte array slice is a well-formed UTF-8 byte sequence, as defined by 117 * {@link #isWellFormed(byte[])}. Note that this can be false even when {@code 118 * isWellFormed(bytes)} is true. 119 * 120 * @param bytes the input buffer 121 * @param off the offset in the buffer of the first byte to read 122 * @param len the number of bytes to read from the buffer 123 */ 124 public static boolean isWellFormed(byte[] bytes, int off, int len) { 125 int end = off + len; 126 checkPositionIndexes(off, end, bytes.length); 127 // Look for the first non-ASCII character. 128 for (int i = off; i < end; i++) { 129 if (bytes[i] < 0) { 130 return isWellFormedSlowPath(bytes, i, end); 131 } 132 } 133 return true; 134 } 135 136 private static boolean isWellFormedSlowPath(byte[] bytes, int off, int end) { 137 int index = off; 138 while (true) { 139 int byte1; 140 141 // Optimize for interior runs of ASCII bytes. 142 do { 143 if (index >= end) { 144 return true; 145 } 146 } while ((byte1 = bytes[index++]) >= 0); 147 148 if (byte1 < (byte) 0xE0) { 149 // Two-byte form. 150 if (index == end) { 151 return false; 152 } 153 // Simultaneously check for illegal trailing-byte in leading position 154 // and overlong 2-byte form. 155 if (byte1 < (byte) 0xC2 || bytes[index++] > (byte) 0xBF) { 156 return false; 157 } 158 } else if (byte1 < (byte) 0xF0) { 159 // Three-byte form. 160 if (index + 1 >= end) { 161 return false; 162 } 163 int byte2 = bytes[index++]; 164 if (byte2 > (byte) 0xBF 165 // Overlong? 5 most significant bits must not all be zero. 166 || (byte1 == (byte) 0xE0 && byte2 < (byte) 0xA0) 167 // Check for illegal surrogate codepoints. 168 || (byte1 == (byte) 0xED && (byte) 0xA0 <= byte2) 169 // Third byte trailing-byte test. 170 || bytes[index++] > (byte) 0xBF) { 171 return false; 172 } 173 } else { 174 // Four-byte form. 175 if (index + 2 >= end) { 176 return false; 177 } 178 int byte2 = bytes[index++]; 179 if (byte2 > (byte) 0xBF 180 // Check that 1 <= plane <= 16. Tricky optimized form of: 181 // if (byte1 > (byte) 0xF4 182 // || byte1 == (byte) 0xF0 && byte2 < (byte) 0x90 183 // || byte1 == (byte) 0xF4 && byte2 > (byte) 0x8F) 184 || (((byte1 << 28) + (byte2 - (byte) 0x90)) >> 30) != 0 185 // Third byte trailing-byte test 186 || bytes[index++] > (byte) 0xBF 187 // Fourth byte trailing-byte test 188 || bytes[index++] > (byte) 0xBF) { 189 return false; 190 } 191 } 192 } 193 } 194 195 private Utf8() {} 196}