blst_radix_gapfind
static int blst_radix_gapfind(blmeta_t *scan, swblk_t blk, swblk_t radix, swblk_t skip,
state = blst_radix_gapfind(bl->bl_root, 0, bl->bl_radix, bl->bl_skip,
state = blst_radix_gapfind(&scan[i], blk, radix, next_skip - 1,