/*
* Copyright (C) 2007, Robin Rosenberg <robin.rosenberg@dewire.com>
* Copyright (C) 2007, Shawn O. Pearce <spearce@spearce.org>
*
* 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 of the Git Development Community 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 org.spearce.jgit.lib;
/**
* Recreate a stream from a base stream and a GIT pack delta.
* <p>
* This entire class is heavily cribbed from <code>patch-delta.c</code> in the
* GIT project. The original delta patching code was written by Nicolas Pitre
* (<nico@cam.org>).
* </p>
*/
public class BinaryDelta {
/**
* Apply the changes defined by delta to the data in base, yielding a new
* array of bytes.
*
* @param base
* some byte representing an object of some kind.
* @param delta
* a git pack delta defining the transform from one version to
* another.
* @return patched base
*/
public static final byte[] apply(final byte[] base, final byte[] delta) {
int deltaPtr = 0;
// Length of the base object (a variable length int).
//
int baseLen = 0;
int c, shift = 0;
do {
c = delta[deltaPtr++] & 0xff;
baseLen |= (c & 0x7f) << shift;
shift += 7;
} while ((c & 0x80) != 0);
if (base.length != baseLen)
throw new IllegalArgumentException("base length incorrect");
// Length of the resulting object (a variable length int).
//
int resLen = 0;
shift = 0;
do {
c = delta[deltaPtr++] & 0xff;
resLen |= (c & 0x7f) << shift;
shift += 7;
} while ((c & 0x80) != 0);
final byte[] result = new byte[resLen];
int resultPtr = 0;
while (deltaPtr < delta.length) {
final int cmd = delta[deltaPtr++] & 0xff;
if ((cmd & 0x80) != 0) {
// Determine the segment of the base which should
// be copied into the output. The segment is given
// as an offset and a length.
//
int copyOffset = 0;
if ((cmd & 0x01) != 0)
copyOffset = delta[deltaPtr++] & 0xff;
if ((cmd & 0x02) != 0)
copyOffset |= (delta[deltaPtr++] & 0xff) << 8;
if ((cmd & 0x04) != 0)
copyOffset |= (delta[deltaPtr++] & 0xff) << 16;
if ((cmd & 0x08) != 0)
copyOffset |= (delta[deltaPtr++] & 0xff) << 24;
int copySize = 0;
if ((cmd & 0x10) != 0)
copySize = delta[deltaPtr++] & 0xff;
if ((cmd & 0x20) != 0)
copySize |= (delta[deltaPtr++] & 0xff) << 8;
if ((cmd & 0x40) != 0)
copySize |= (delta[deltaPtr++] & 0xff) << 16;
if (copySize == 0)
copySize = 0x10000;
System.arraycopy(base, copyOffset, result, resultPtr, copySize);
resultPtr += copySize;
} else if (cmd != 0) {
// Anything else the data is literal within the delta
// itself.
//
System.arraycopy(delta, deltaPtr, result, resultPtr, cmd);
deltaPtr += cmd;
resultPtr += cmd;
} else {
// cmd == 0 has been reserved for future encoding but
// for now its not acceptable.
//
throw new IllegalArgumentException("unsupported command 0");
}
}
return result;
}
}