XeNTaX

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typedef struct gmiCmpHdr_s
{
	BYTE			id[4]; //"CMPS"
	int				cmpType;
	int				decompSize;
	int				resv;
} gmiCmpHdr_t;

//decompress data
static BYTE *Model_GMI_Decompress(BYTE *src, int &len, noeRAPI_t *rapi)
{
	gmiCmpHdr_t *cmpHdr = (gmiCmpHdr_t *)src;
	int srcLen = len;
	int dstLen = cmpHdr->decompSize;
	BYTE *dst = (BYTE *)rapi->Noesis_PooledAlloc(dstLen);
	int srcPtr = sizeof(gmiCmpHdr_t);
	int dstPtr = 0;

	while (srcPtr < srcLen && dstPtr < dstLen)
	{
		BYTE ctrl = src[srcPtr++];
		for (int i = 0; i < 8 && srcPtr < srcLen && dstPtr < dstLen; i++)
		{
			if (ctrl & (1<<i))
			{ //literal
				dst[dstPtr++] = src[srcPtr++];
			}
			else
			{ //ofs+len
				WORD ol = *(WORD *)(src+srcPtr);
				srcPtr += sizeof(WORD);
				int len = 3 + ((ol>>8) & 15);
				int relOfs = (ol & 255) | ((ol>>12) << 8);
				int ofs = dstPtr - ((dstPtr-18-relOfs) & 4095);
				for (int j = 0; j < len && dstPtr < dstLen; j++)
				{
					if (ofs+j < 0 || ofs+j >= dstPtr)
					{
						dst[dstPtr++] = 0;
					}
					else
					{
						dst[dstPtr++] = dst[ofs+j];
					}
				}
			}
		}
	}
	assert(srcPtr <= srcLen);
	assert(dstPtr <= dstLen);

	len = dstLen;
	return dst;
}

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int len = 3 + ((ol>>8) & 15);

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int relOfs = (ol & 255) | ((ol>>12) << 8);

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int ofs = dstPtr - ((dstPtr-18-relOfs) & 4095);

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for (int i = 0; i < 8 && srcPtr < srcLen && dstPtr < dstLen; i++)
{
  if (ctrl & (1<<i))

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WORD ol = *(WORD *)(src+srcPtr);

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srcPtr += sizeof(WORD);

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private static void decompress(File compressedFile) throws Exception {
	// create a stream to read the input
	DataInputStream is = new DataInputStream(new FileInputStream(compressedFile));
	// skip the first 8 bytes
	is.skipBytes(8); // C M P S 01 00 00 00
	// read the next int which is the decompressed size
	int dstLen = Integer.reverseBytes(is.readInt()); // The 4 bytes are read in the reverse order
	// skip 4 more bytes
	is.skipBytes(4); // 00 00 00 00

	// for the sake of simplicity reads the entire file to a byte array, ignoring the first 16 bytes that have already been read.
	int srcLen = (int)compressedFile.length() - 16;
	System.out.println("Source length: " + srcLen);
	byte[] src = new byte[srcLen];
	is.read(src);
	// creates a byte array to store the decompressed bytes
	byte[] dst = new byte[dstLen];
	System.out.println("output length: " + dstLen);

	int srcPtr = 0; // by skipping 16 bytes I can start from 0
	int dstPtr = 0;

	while (srcPtr < srcLen && dstPtr < dstLen) {
		byte ctrl = src[srcPtr++];

		for (int i = 0; i < 8 && srcPtr < srcLen && dstPtr < dstLen; i++) {
			if ( (ctrl & (1 << i)) != 0 ) {
				dst[dstPtr++] = src[srcPtr++];
			}
			else {
				// The line below is different from the original. I'm just reading two bytes from te input
				short ol = (short)(src[srcPtr] << 8 | src[srcPtr + 1]); // should I reverse the byte order?
				// I've read 2 bytes, so I mode the pointer 2 bytes ahead
				srcPtr += 2;
				int len = 3 + ((ol >> 8) & 15); // why +3?
				int relOfs = (ol & 255) | ((ol >> 12) << 8);
				int ofs = dstPtr - ((dstPtr - 18 - relOfs) & 4095); // can't get this 18 and the rest
				for (int j = 0; j < len && dstPtr < dstLen; j++) {
					if (ofs + j < 0 || ofs + j >= dstPtr) {
						dst[dstPtr++] = 0;
					}
					else {
						dst[dstPtr++] = dst[ofs + j];
					}
				}
			}
		}
	}
	// check consistency
	if (srcPtr > srcLen || dstPtr > dstLen) {
		throw new Exception("Out of bounds.");
	}
	// write the decompressed bytes to a file
	OutputStream os = new FileOutputStream( new File(compressedFile.getParent(), compressedFile.getName() + "_DECMPS") );
	os.write( dst );
	os.flush();
}