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/*
* Copyright (c) 2008, Harald Kuhr
* All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions are met:
* * Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
* * Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in the
* documentation and/or other materials provided with the distribution.
* * Neither the name "TwelveMonkeys" nor the
* names of its contributors may be used to endorse or promote products
* derived from this software without specific prior written permission.
*
* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
* "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
* LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
* A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR
* CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
* EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
* PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
* PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
* LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
* NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
* SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
*/
package com.twelvemonkeys.io.enc;
import java.io.OutputStream;
import java.io.IOException;
/**
* Encoder implementation for Apple PackBits run-length encoding.
*
* From Wikipedia, the free encyclopedia
* PackBits is a fast, simple compression scheme for run-length encoding of
* data.
*
* Apple introduced the PackBits format with the release of MacPaint on the
* Macintosh computer. This compression scheme is one of the types of
* compression that can be used in TIFF-files.
*
* A PackBits data stream consists of packets of one byte of header followed by
* data. The header is a signed byte; the data can be signed, unsigned, or
* packed (such as MacPaint pixels).
*
* Header byte Data 0 to 127 1 + n literal bytes of data 0 to -127 One byte of data, repeated 1 - n times in
* the decompressed output -128 No operation
*
* Note that interpreting 0 as positive or negative makes no difference in the
* output. Runs of two bytes adjacent to non-runs are typically written as
* literal data.
*
* See Understanding PackBits
*
* @author Harald Kuhr
* @version $Id: //depot/branches/personal/haraldk/twelvemonkeys/release-2/twelvemonkeys-core/src/main/java/com/twelvemonkeys/io/enc/PackBitsEncoder.java#1 $
*/
public final class PackBitsEncoder implements Encoder {
final private byte[] mBuffer = new byte[128];
/**
* Creates a {@code PackBitsEncoder}.
*/
public PackBitsEncoder() {
}
public void encode(OutputStream pStream, byte[] pBuffer, int pOffset, int pLength) throws IOException {
// NOTE: It's best to encode a 2 byte repeat
// run as a replicate run except when preceded and followed by a
// literal run, in which case it's best to merge the three into one
// literal run. Always encode 3 byte repeats as replicate runs.
// NOTE: Worst case: output = input + (input + 127) / 128
int offset = pOffset;
final int max = pOffset + pLength - 1;
final int maxMinus1 = max - 1;
while (offset <= max) {
// Compressed run
int run = 1;
byte replicate = pBuffer[offset];
while(run < 127 && offset < max && pBuffer[offset] == pBuffer[offset + 1]) {
offset++;
run++;
}
if (run > 1) {
offset++;
pStream.write(-(run - 1));
pStream.write(replicate);
}
// Literal run
run = 0;
while ((run < 128 && ((offset < max && pBuffer[offset] != pBuffer[offset + 1])
|| (offset < maxMinus1 && pBuffer[offset] != pBuffer[offset + 2])))) {
mBuffer[run++] = pBuffer[offset++];
}
// If last byte, include it in literal run, if space
if (offset == max && run > 0 && run < 128) {
mBuffer[run++] = pBuffer[offset++];
}
if (run > 0) {
pStream.write(run - 1);
pStream.write(mBuffer, 0, run);
}
// If last byte, and not space, start new literal run
if (offset == max && (run <= 0 || run >= 128)) {
pStream.write(0);
pStream.write(pBuffer[offset++]);
}
}
}
}