// Some helper functions. As helpful as Spike the Dragon! :)
-// 除法向上取整
+// 除法 v/(2^k) 向上取整
#define CEIL(v, k) (((v) + (1 << (k)) - 1) >> (k))
#define ICEIL(x, y) ((x) / (y) + ((x) % (y) != 0))
-// 除法向下取整
+// 除法 v/(2^k) 向下取整
#define FLOOR(v, k) ((v) >> (k))
// 获取v最近的最大k倍数