public boolean isNodeUsed(int nodeIndex) {
		int block = bitmap[nodeIndex / 8] & 0xff;
		return (block & (1 << 7 - (nodeIndex % 8))) != 0;
	}
Returns  true if the specified node index is used.
Returns false if the specified node index is free.
@param nodeIndex the node index
@return true if the specified node index is used, false if free
GPL/DMG/src/dmg/java/mobiledevices/dmg/btree/BTreeMapRecord.java