src/main/java/org/apache/commons/sanselan/common/mylzw/MyBitInputStream.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 org.apache.commons.sanselan.common.mylzw;

import java.io.IOException;
import java.io.InputStream;

import org.apache.commons.sanselan.common.BinaryConstants;

public class MyBitInputStream extends InputStream implements BinaryConstants
{
    private final InputStream is;
    private final int byteOrder;
    private boolean tiffLZWMode = false;

    public MyBitInputStream(InputStream is, int byteOrder)
    {
        this.byteOrder = byteOrder;
        this.is = is;
    }

    @Override
    public int read() throws IOException
    {
        return readBits(8);
    }

    private long bytesRead = 0;
    private int bitsInCache = 0;
    private int bitCache = 0;

    public void setTiffLZWMode()
    {
        tiffLZWMode = true;
    }

    public int readBits(int SampleBits) throws IOException
    {
        while (bitsInCache < SampleBits)
        {
            int next = is.read();

            if (next < 0)
            {
                if (tiffLZWMode)
                {
                    // pernicious special case!
                    return 257;
                }
                return -1;
            }

            int newByte = (0xff & next);

            if (byteOrder == BYTE_ORDER_NETWORK) // MSB, so add to right
                bitCache = (bitCache << 8) | newByte;
            else if (byteOrder == BYTE_ORDER_INTEL) // LSB, so add to left
                bitCache = (newByte << bitsInCache) | bitCache;
            else
                throw new IOException("Unknown byte order: " + byteOrder);

            bytesRead++;
            bitsInCache += 8;
        }
        int sampleMask = (1 << SampleBits) - 1;

        int sample;

        if (byteOrder == BYTE_ORDER_NETWORK) // MSB, so read from left
        {
            sample = sampleMask & (bitCache >> (bitsInCache - SampleBits));
        }
        else if (byteOrder == BYTE_ORDER_INTEL) // LSB, so read from right
        {
            sample = sampleMask & bitCache;
            bitCache >>= SampleBits;
        }
        else
            throw new IOException("Unknown byte order: " + byteOrder);

        int result = sample;

        bitsInCache -= SampleBits;
        int remainderMask = (1 << bitsInCache) - 1;
        bitCache &= remainderMask;

        return result;
    }

    public void flushCache()
    {
        bitsInCache = 0;
        bitCache = 0;
    }

    public long getBytesRead()
    {
        return bytesRead;
    }

}