typedef union {
 short W; /* Word access */
 struct { /* Byte access */
#ifdef LOW_ENDIAN
 byte low, high; /* in low-endian arch */
#else
 byte high, low; /* in high-endian arch */
#endif
 } B;
} word;

a = a % 8;
=>
a = a & 7;

a = pow(a, 2.0);
=>
a = a * a;

a = a * 4;
b = b / 4;
=>
a = a << 2;
b = b >> 2;

a = a * 9;
=>
a = (a << 3) + a;

typedef unsigned char  boolean; /* Boolean value type. */
typedef unsigned long int uint32; /* Unsigned 32 bit value */
typedef unsigned short  uint16; /* Unsigned 16 bit value */
typedef unsigned char  uint8; /* Unsigned 8 bit value */
typedef signed long int  int32; /* Signed 32 bit value */
typedef signed short  int16; /* Signed 16 bit value */
typedef signed char   int8; /* Signed 8 bit value */

typedef unsigned char byte; /* Unsigned 8 bit value type */ 
typedef unsigned short word; /* Unsigned 16 bit value type */

#define MEM_B(x) (*((byte*)(x)))
#define MEM_W(x) (*((word*)(x)))

#define MAX(x, y) ((x) > (y) ? (x) : (y))
#define MIN(x, y) ((x) < (y) ? (x) : (y))

typedef unsigned long dword; /* Unsigned 32 bit value type */

#define FPOS(type, field)\
 ( (dword)&((type*)0)->field )

#define FSIZE(type, field)\
 ( sizeof(((type*)0)->field) )

#define FLOPW(ray, val)\
 do {\
  (ray)[0] = ((val)>>8);\
  (ray)[1] = ((val)&0xFF);\
 }while(0);

typedef unsigned char byte; /* Unsigned 8 bit value type */
typedef unsigned short word; /* Unsigned 16 bit value type */ 

#define B_PTR(var) ((byte*)(void*)&(var))
#define W_PTR(var) ((word*)(void*)&(var))

typedef unsigned char byte; /* Unsigned 8 bit value type */
typedef unsigned short word; /* Unsigned 16 bit value type */

#define WORD_L(var) ((byte)(word)(var)&(0xFF))
#define WORD_H(var) ((byte)(word)(var)>>(8))

#define INC_SAT(val)\
 ((val) = ( ((val) + 1) > (val)) ? ((val) + 1):(val) )

#define ARR_SIZE(a)\
 ( (sizeof(a)) / (sizeof(a[0])) )

typedef unsigned long dword; /* Unsigned 32 bit value type */ 

#define MOD_BY_POWER_OF_TWO(val, mod_by)\
 ((dword)(val)&(dword)(2<<(mod_by) - 1))

typedef unsigned char byte; /* Unsigned 8 bit value type */
typedef unsigned short word; /* Unsigned 16 bit value type */
typedef unsigned long dword; /* Unsigned 32 bit value type */

#define outp(port)  (*((volatile byte *)(port)))
#define outpw(port)  (*((volatile word *)(port)))
#define outpdw(port) (*((volatile dword *)(port)))

#define inp(port, val)  (*((volatile byte *)(port))) = (byte)(val)
#define inpw(port, val)  (*((volatile word *)(port))) = (word)(val)
#define inpdw(port, val) (*((volatile dword *)(port))) = (dword)(val)

 #define STR(val) (#val)
 #define CONS(a, b) (int)(a##e##b)
 ->
 STR(hello) ==> "hello"
 CONS(2, 3) ==> 2000 // 2e3

  #define TOW   (2)
  #define MUL(a,b) (a*b)

  printf("%d*%d=%d\n", TOW, TOW, MUL(TOW,TOW));
  ==>
  printf("%d*%d=%d\n", (2), (2), ((2)*(2)));

  #define A   (2)
  #define STR(s)  #s
  #define CONS(a,b) int(a##e##b)

  printf("int max: %s\n", STR(INT_MAX)); // INT_MAX #include
  ==>
  printf("int max: %s\n", "INT_MAX"); 

  printf("%s\n", CONS(A, A));    // compile error
  ==>
  printf("%s\n", int(AeA));

  #define A   (2)   
  #define _STR(s)  (#s)
  #define STR(s)  _STR(s)  // 转换宏
  #define _CONS(a,b) int(a##e##b)
  #define CONS(a,b) _CONS(a,b) // 转换宏

  printf("int max: %s\n", STR(INT_MAX)); // INT_MAX,int型的最大值，为一个变量 #include

  STR(INT_MAX) --> _STR(0x7fffffff) 然后再转换成字符串;
  printf("%d\n", CONS(A, A));

  #define ___ANONYMOUS1(type, var, line) type var##line
  #define __ANONYMOUS0(type, line)  ___ANONYMOUS1(type, _anonymous, line)
  #define ANONYMOUS(type)     __ANONYMOUS0(type, __LINE__)

  #define FILL(a)  {a, #a}
  enum IDD {OPEN, CLOSE};
  typedef struct MSG{
   IDD id;
   const char * msg;
  }MSG;

  MSG _msg[] = {FILL(OPEN), FILL(CLOSE)};
  ==>
  MSG _msg[] = {{OPEN, "OPEN"},

  {CLOSE, "CLOSE"}};

  #define _GET_FILE_NAME(f) #f
  #define GET_FILE_NAME(f) _GET_FILE_NAME(f)

  static char FILE_NAME[]  = GET_FILE_NAME(__FILE__);

  #define _TYPE_BUF_SIZE(type) sizeof #type
  #define TYPE_BUF_SIZE(type)  _TYPE_BUF_SIZE(type) 

  char buf[TYPE_BUF_SIZE(INT_MAX)]; 
  --> char buf[_TYPE_BUF_SIZE(0x7fffffff)]; 
  --> char buf[sizeof "0x7fffffff"];