+ size_t key_size; /* key size */
+ char *buf_mem; /* window buffer */
+ size_t buf_size; /* size of window */
+ size_t pos_end; /* last position in set */
+ size_t pos_cur; /* current position in set */
+ size_t pos_buf; /* position of first byte in window */
+ size_t pos_border; /* position of last byte+1 in window */
+ int dirty; /* window is dirty */