src/main/java/org/apache/commons/sanselan/common/BitInputStreamFlexible.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;

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

public class BitInputStreamFlexible extends InputStream
        implements
            BinaryConstants
{
    // TODO should be byte order conscious, ie TIFF for reading
    // samples size<8 - shuoldn't that effect their order within byte?
    private final InputStream is;

    public BitInputStreamFlexible(InputStream is)
    {
        this.is = is;
        //            super(is);
    }

    @Override
    public int read() throws IOException
    {
        if (cacheBitsRemaining > 0)
            throw new IOException("BitInputStream: incomplete bit read");
        return is.read();
    }

    private int cache;
    private int cacheBitsRemaining = 0;
    private long bytesRead = 0;

    public final int readBits(int count) throws IOException
    {

        if (count <= 32) // catch-all
        {
            int result = 0;
            //            int done = 0;

            if (cacheBitsRemaining > 0)
            {
                if (count >= cacheBitsRemaining)
                {
                    result = ((1 << cacheBitsRemaining) - 1) & cache;
                    count -= cacheBitsRemaining;
                    cacheBitsRemaining = 0;
                }
                else
                {
                    //                    cache >>= count;
                    cacheBitsRemaining -= count;
                    result = ((1 << count) - 1) & (cache >> cacheBitsRemaining);
                    count = 0;
                }
            }
            while (count >= 8)
            {
                cache = is.read();
                if (cache < 0)
                    throw new IOException("couldn't read bits");
//                System.out.println("cache 1: " + cache + " ("
//                        + Integer.toHexString(cache) + ", "
//                        + Integer.toBinaryString(cache) + ")");
                bytesRead++;
                result = (result << 8) | (0xff & cache);
                count -= 8;
            }
            if (count > 0)
            {
                cache = is.read();
                if (cache < 0)
                    throw new IOException("couldn't read bits");
//                System.out.println("cache 2: " + cache + " ("
//                        + Integer.toHexString(cache) + ", "
//                        + Integer.toBinaryString(cache) + ")");
                bytesRead++;
                cacheBitsRemaining = 8 - count;
                result = (result << count)
                        | (((1 << count) - 1) & (cache >> cacheBitsRemaining));
                count = 0;
            }

            return result;
        }

        throw new IOException("BitInputStream: unknown error");

    }

    public void flushCache()
    {
        cacheBitsRemaining = 0;
    }

    public long getBytesRead()
    {
        return bytesRead;
    }
}