_CAT_HDR_SIZE
n = _CAT_HDR_SIZE + mem;
set = (struct _cat_set_hdr *) (cat + _CAT_HDR_SIZE);
i = read_block(fd, (char *) &hdr, _CAT_HDR_SIZE, pathname);
if (i < _CAT_HDR_SIZE || hdr.__nsets < 0) {
+ _CAT_HDR_SIZE
+ _CAT_HDR_SIZE
+ _CAT_HDR_SIZE