luni/src/main/java/java/nio/charset/ModifiedUtf8.java

/*
 *  Licensed to the Apache Software Foundation (ASF) under one or more
 *  contributor license agreements.  See the NOTICE file distributed with
 *  this work for additional information regarding copyright ownership.
 *  The ASF licenses this file to You under the Apache License, Version 2.0
 *  (the "License"); you may not use this file except in compliance with
 *  the License.  You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 *  Unless required by applicable law or agreed to in writing, software
 *  distributed under the License is distributed on an "AS IS" BASIS,
 *  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 *  See the License for the specific language governing permissions and
 *  limitations under the License.
 */

package java.nio.charset;

import java.io.UTFDataFormatException;

/**
 * @hide internal use only
 */
public class ModifiedUtf8 {
    /**
     * Decodes a byte array containing <i>modified UTF-8</i> bytes into a string.
     *
     * <p>Note that although this method decodes the (supposedly impossible) zero byte to U+0000,
     * that's what the RI does too.
     */
    public static String decode(byte[] in, char[] out, int offset, int utfSize) throws UTFDataFormatException {
        int count = 0, s = 0, a;
        while (count < utfSize) {
            if ((out[s] = (char) in[offset + count++]) < '\u0080') {
                s++;
            } else if (((a = out[s]) & 0xe0) == 0xc0) {
                if (count >= utfSize) {
                    throw new UTFDataFormatException("bad second byte at " + count);
                }
                int b = in[offset + count++];
                if ((b & 0xC0) != 0x80) {
                    throw new UTFDataFormatException("bad second byte at " + (count - 1));
                }
                out[s++] = (char) (((a & 0x1F) << 6) | (b & 0x3F));
            } else if ((a & 0xf0) == 0xe0) {
                if (count + 1 >= utfSize) {
                    throw new UTFDataFormatException("bad third byte at " + (count + 1));
                }
                int b = in[offset + count++];
                int c = in[offset + count++];
                if (((b & 0xC0) != 0x80) || ((c & 0xC0) != 0x80)) {
                    throw new UTFDataFormatException("bad second or third byte at " + (count - 2));
                }
                out[s++] = (char) (((a & 0x0F) << 12) | ((b & 0x3F) << 6) | (c & 0x3F));
            } else {
                throw new UTFDataFormatException("bad byte at " + (count - 1));
            }
        }
        return new String(out, 0, s);
    }

    private ModifiedUtf8() {
    }
}