# RunLengthDecodeFilter.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.pdfbox.filter;

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

    import org.apache.pdfbox.cos.COSDictionary;

    /**
     * Decompresses data encoded using a byte-oriented run-length encoding algorithm,
     * reproducing the original text or binary data
     *
     * @author Ben Litchfield
     * @author Tilman Hausherr
     */
    final class RunLengthDecodeFilter extends Filter
    {
        private static final int RUN_LENGTH_EOD = 128;

        @Override
        public DecodeResult decode(InputStream encoded, OutputStream decoded,
                                             COSDictionary parameters, int index) throws IOException
        {
            int dupAmount;
            byte[] buffer = new byte[128];
            while ((dupAmount = encoded.read()) != -1 && dupAmount != RUN_LENGTH_EOD)
            {
                if (dupAmount <= 127)
                {
                    int amountToCopy = dupAmount + 1;
                    int compressedRead;
                    while (amountToCopy > 0)
                    {
                        compressedRead = encoded.read(buffer, 0, amountToCopy);
                        // EOF reached?
                        if (compressedRead == -1)
                        {
                            break;
                        }
                        decoded.write(buffer, 0, compressedRead);
                        amountToCopy -= compressedRead;
                    }
                }
                else
                {
                    int dupByte = encoded.read();
                    // EOF reached?
                    if (dupByte == -1)
                    {
                        break;
                    }
                    for (int i = 0; i < 257 - dupAmount; i++)
                    {
                        decoded.write(dupByte);
                    }
                }
            }
            return new DecodeResult(parameters);
        }

        @Override
        protected void encode(InputStream input, OutputStream encoded, COSDictionary parameters)
                throws IOException
        {
            // Not used in PDFBox except for testing the decoder.
            int lastVal = -1;
            int byt;
            int count = 0;
            boolean equality = false;

            // buffer for "unequal" runs, size between 2 and 128
            byte[] buf = new byte[128];

            while ((byt = input.read()) != -1)
            {
                if (lastVal == -1)
                {
                    // first time
                    lastVal = byt;
                    count = 1;
                }
                else
                {
                    if (count == 128)
                    {
                        if (equality)
                        {
                            // max length of equals
                            encoded.write(129); // = 257 - 128
                            encoded.write(lastVal);
                        }
                        else
                        {
                            // max length of unequals
                            encoded.write(127);
                            encoded.write(buf, 0, 128);
                        }
                        equality = false;
                        lastVal = byt;
                        count = 1;
                    }
                    else if (count == 1)
                    {
                        if (byt == lastVal)
                        {
                            equality = true;
                        }
                        else
                        {
                            buf[0] = (byte) lastVal;
                            buf[1] = (byte) byt;
                            lastVal = byt;
                        }
                        count = 2;
                    }
                    else
                    {
                        // 1 < count < 128
                        if (byt == lastVal)
                        {
                            if (equality)
                            {
                                ++count;
                            }
                            else
                            {
                                // write all we got except the last
                                encoded.write(count - 2);
                                encoded.write(buf, 0, count - 1);
                                count = 2;
                                equality = true;
                            }
                        }
                        else
                        {
                            if (equality)
                            {
                                // equality ends here
                                encoded.write(257 - count);
                                encoded.write(lastVal);
                                equality = false;
                                count = 1;
                            }
                            else
                            {
                                buf[count] = (byte) byt;
                                ++count;
                            }
                            lastVal = byt;
                        }
                    }
                }
            }
            if (count > 0)
            {
                if (count == 1)
                {
                    encoded.write(0);
                    encoded.write(lastVal);
                }
                else if (equality)
                {
                    encoded.write(257 - count);
                    encoded.write(lastVal);
                }
                else
                {
                    encoded.write(count - 1);
                    encoded.write(buf, 0, count);
                }
            }
            encoded.write(RUN_LENGTH_EOD);
        }
    }