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/*
 * Copyright 2014 Volker Oth (0xdeadbeef) / Miklos Juhasz (mjuhasz)
 *
 * Licensed 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 bdsup2sub.tools;

/**
 * Simple helper class to read bitwise from a buffer.
 */
public class BitStream {

    /** Data buffer */
    private final byte buffer[];
    /** Offset to current byte in buffer */
    private int byteOfs;
    /** Current byte from the buffer */
    private int b;
    /** Bits left in current byte b */
    private int bits;

    /**
     * @param buffer Byte array to create bitstream for
     */
    public BitStream(byte buffer[]) {
        this.buffer = buffer;
        byteOfs = 0;	// start with first byte
        b = buffer[0] & 0xff;
        bits = 8;		// 8 bits left in b
    }

    /**
     * @return Number of bits left in buffer
     */
    public int bitsLeft() {
        return 8 * (buffer.length - byteOfs) - (8 - bits);
    }

    /**
     * Read n bits from buffer (n <= 32)
     * @param n Number of bits to read from buffer (n<=32)
     * @return Value containing the n bits (last bit read is LSB)
     */
    public int readBits(int n) {
        int retval = 0;
        while (n>0) {
            // bit by bit
            retval <<= 1;
            if ((b & 0x80) == 0x80) {
                retval |= 1; // get next bit
            }
            b <<= 1;
            n--;
            if (--bits==0) {
                if (byteOfs