用于对齐：向上对齐和向下对齐：
#define ROUND_UP(x, align) (((int) (x) + (align – 1)) & ~(align – 1)
)#define ROUND_DOWN(x, align) ((int)(x) & ~(align – 1))用于检查是否已经对齐：
#define ALIGNED(x, align) (((int)(x) & (align – 1)) == 0)其中，x为要计算或者检查的值，align是要对齐的单位例如：
#define _ALLOC_ALIGN_SIZE 16#define MEM_ROUND_UP(x) ROUND_UP(x, _ALLOC_ALIGN_SIZE)#define MEM_ROUND_DOWN(x) ROUND_DOWN(x, _ALLOC_ALIGN_SIZE)
