X-tree的C++源码，对应文章S. Berchtold, D. A. Keim, H.-P. Kriegel: The X-tree : An Index Structure for High-Dimensional Data. -X-tree in C source code, the corresponding articles S. Berchtold, D. A. Keim. H.-P. Kriegel : The X-tree : An Index Structure for High-Dimensional Data.