int index = 128 * (col - cGroup) + (row - rGroup);
FileInputStream isBundlx = new FileInputStream(bundlxFileName);
isBundlx.skip(16 + 5 * index);
byte[] buffer = new byte[5];
isBundlx.read(buffer);
long offset = (long) (buffer[0] & 0xff) + (long) (buffer[1] & 0xff)
* 256 + (long) (buffer[2] & 0xff) * 65536
+ (long) (buffer[3] & 0xff) * 16777216
+ (long) (buffer[4] & 0xff) * 4294967296L; FileInputStream isBundle = new FileInputStream(bundleFileName);
isBundle.skip(offset);
byte[] lengthBytes = new byte[4];
isBundle.read(lengthBytes);
int length = (int) (lengthBytes[0] & 0xff)
+ (int) (lengthBytes[1] & 0xff) * 256
+ (int) (lengthBytes[2] & 0xff) * 65536
+ (int) (lengthBytes[3] & 0xff) * 16777216;
result = new byte[length];
isBundle.read(result);
上面这段用Objective-C应该怎么写啊