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      1 /*
      2  * Copyright (C) 2011 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.dex;
     18 
     19 import com.android.dex.util.ByteInput;
     20 import java.io.UTFDataFormatException;
     21 
     22 /**
     23  * Modified UTF-8 as described in the dex file format spec.
     24  *
     25  * <p>Derived from libcore's MUTF-8 encoder at java.nio.charset.ModifiedUtf8.
     26  */
     27 public final class Mutf8 {
     28     private Mutf8() {}
     29 
     30     /**
     31      * Decodes bytes from {@code in} into {@code out} until a delimiter 0x00 is
     32      * encountered. Returns a new string containing the decoded characters.
     33      */
     34     public static String decode(ByteInput in, char[] out) throws UTFDataFormatException {
     35         int s = 0;
     36         while (true) {
     37             char a = (char) (in.readByte() & 0xff);
     38             if (a == 0) {
     39                 return new String(out, 0, s);
     40             }
     41             out[s] = a;
     42             if (a < '\u0080') {
     43                 s++;
     44             } else if ((a & 0xe0) == 0xc0) {
     45                 int b = in.readByte() & 0xff;
     46                 if ((b & 0xC0) != 0x80) {
     47                     throw new UTFDataFormatException("bad second byte");
     48                 }
     49                 out[s++] = (char) (((a & 0x1F) << 6) | (b & 0x3F));
     50             } else if ((a & 0xf0) == 0xe0) {
     51                 int b = in.readByte() & 0xff;
     52                 int c = in.readByte() & 0xff;
     53                 if (((b & 0xC0) != 0x80) || ((c & 0xC0) != 0x80)) {
     54                     throw new UTFDataFormatException("bad second or third byte");
     55                 }
     56                 out[s++] = (char) (((a & 0x0F) << 12) | ((b & 0x3F) << 6) | (c & 0x3F));
     57             } else {
     58                 throw new UTFDataFormatException("bad byte");
     59             }
     60         }
     61     }
     62 
     63     /**
     64      * Returns the number of bytes the modified UTF8 representation of 's' would take.
     65      */
     66     private static long countBytes(String s, boolean shortLength) throws UTFDataFormatException {
     67         long result = 0;
     68         final int length = s.length();
     69         for (int i = 0; i < length; ++i) {
     70             char ch = s.charAt(i);
     71             if (ch != 0 && ch <= 127) { // U+0000 uses two bytes.
     72                 ++result;
     73             } else if (ch <= 2047) {
     74                 result += 2;
     75             } else {
     76                 result += 3;
     77             }
     78             if (shortLength && result > 65535) {
     79                 throw new UTFDataFormatException("String more than 65535 UTF bytes long");
     80             }
     81         }
     82         return result;
     83     }
     84 
     85     /**
     86      * Encodes the modified UTF-8 bytes corresponding to {@code s} into  {@code
     87      * dst}, starting at {@code offset}.
     88      */
     89     public static void encode(byte[] dst, int offset, String s) {
     90         final int length = s.length();
     91         for (int i = 0; i < length; i++) {
     92             char ch = s.charAt(i);
     93             if (ch != 0 && ch <= 127) { // U+0000 uses two bytes.
     94                 dst[offset++] = (byte) ch;
     95             } else if (ch <= 2047) {
     96                 dst[offset++] = (byte) (0xc0 | (0x1f & (ch >> 6)));
     97                 dst[offset++] = (byte) (0x80 | (0x3f & ch));
     98             } else {
     99                 dst[offset++] = (byte) (0xe0 | (0x0f & (ch >> 12)));
    100                 dst[offset++] = (byte) (0x80 | (0x3f & (ch >> 6)));
    101                 dst[offset++] = (byte) (0x80 | (0x3f & ch));
    102             }
    103         }
    104     }
    105 
    106     /**
    107      * Returns an array containing the <i>modified UTF-8</i> form of {@code s}.
    108      */
    109     public static byte[] encode(String s) throws UTFDataFormatException {
    110         int utfCount = (int) countBytes(s, true);
    111         byte[] result = new byte[utfCount];
    112         encode(result, 0, s);
    113         return result;
    114     }
    115 }
    116