C language bit operation

In the C language, it is sometimes necessary to perform a bitwise operation, such as for some of these bits. The purpose of this is to achieve the goal, without affecting the other bits. The usual set-up operations are as follows:

#define SETBIT (x, y) x|= (1<<y)//x Y position 1
#define CLRBIT (x, y) x&=~ (1<<y)//The Y-position of X is clear 0

As an example:

int main (int argc, char* argv[])
{
unsigned char a = 0x55;
unsigned char b = a|      (1<<1); First position 1
unsigned char c = a&~ (1<<2); Second position 0
printf ("Hello world! 0x%x,0x%x/n ", b,c);
return 0;
}

Output 0x57,0x51. 0x57 is from 01010101 to 01010111;0x51 i.e. from 01010101 to 01010001.

First, basic bit operation

|	Or
&	And
~	Take counter
^	XOR or
<<	Move left
>>	Move right

Common usage of bitwise operation

1. Get the value of a bit

1. #define Bitget (Number,pos) ((number) |= 1<< (POS))//place a position 1
2. #define Bitget (Number,pos) ((number) &= ~ (1<< (POS))//Position 0
3. #define Bitget (Number,pos) ((number) >> (POS) &1))//Use a macro to get a bit of a number
4. #define Bitget (Number,pos) ((number) ^= 1<< (POS))//reverse the POS bit of number

2. Set the value of a bit (set to 0 or 1)

Method One:

1. #define SETBIT (x, y) x|= (1<<y)//x Y position 1
2. #define CLRBIT (x, y) x&=~ (1<<y)//The Y-position of X is clear 0

Method Two:

Set 0, use 0 to go ' with '

int a|= (1<<X) x is a number that requires 1, such as fourth position 1: = "" a|= "(1<<4)

Set 1, use 1 to go ' or '
int a&=~ (1<<x) 0<= a position "p=" >

3. Cyclic shift

1. #define ROTATE_LEFT (x, N) ((x) << (n)) | ((x) >> ((8 * sizeof (x))-(n)))
2. #define Rotate_right (x, N) ((x) >> (n)) | ((x) << ((8 * sizeof (x))-(n)))

4. Calculate absolute Value

1. int abs (int x)
2. {
3. int y;
4. y = x>>31;
5. Return (x^y)-y; Or: (x+y) ^y
6. }

5. Judging the symbols of integers

1. int sign (int x)
2. {
3. Return (X>>31) | (unsigned (x)) >>31;
4. }

6. Two number comparison

1. X==y: ~ (x-y|y-x)
2. X!=y:x-y|y-x
3. X<y: (x-y) ^ ((x^y) & ((x-y) ^x))
4. X<=y: (X|~y) & ((x^y) |~ (y-x))
5. X<y: (~x&y) | ((~x|y) & (x-y))//unsigned x, y comparison
6. X<=y: (~x|y) & ((x^y) |~ (y-x))//unsigned x, y comparison

7. Exchange two-digit value (swap)

1. 1.x ^= y; Y ^= x; x ^= y;
2. 2.x = X+y; y = x-y; x = XY;
3. 3.x = x-y; y = y+x; x = y-x;
4. 4.x = Y-x; x = y-x; x = X+y;

8. Bit count

2. Method One:
4. int count (Long v)
6. {
8. int number = 0;
12. while (v)
14. {
16. V &= (V-1);
18. number++;
20. }
22. return number;
24. }
26. Method Two:
28. int count (unsigned x)
30. {
32. × = X ((x>>1) &0x55555555);
34. x = (x&0x33333333) + (x>>2) &0x33333333);
36. x = (x+ (x>>4)) &0x0f0f0f0f;
38. x = x+ (x>>8);
40. x = x+ (x>>16);
42. Return x&0x0000003f;
44. }

9. Conversion of binary and gray codes

1. (1). Conversion of binary code to Gray code:  
2.   unsigned b2g (unsigned b )  
3.   { 
4.       return B ^  (b>>1)  ; 
5.   } 
6.    (2). Gray code to binary code: &NBSP;
7.   unsigned g2b (unsigned G)  
8.  {
9.    & nbsp; unsigned b ; 
10.      b = g ^  (G>>1)  ; 
11.      b = g ^  (g>>2)  ; 
12.      b = g ^  (g>>4)  ; 
13.       b = g ^  (g>>8)  ; 
14.      b = g ^   (g>>16)  ; 
15.      return b ;
16.   }

10. Bit reversal

1. Unsigned rev (unsigned x)
2. {
3. x = (x & 0x55555555) << 1 | (x>>1) & 0x55555555;
4. x = (x & 0x33333333) << 2 | (x>>2) & 0x33333333;
5. x = (x & 0x0f0f0f0f) << 4 | (x>>4) & 0x0f0f0f0f;
6. x = (x<<24) | ((x&0xff00) <<8) | ((x>>8) & 0xff00) | (x>>24);
7. return x;
8. }

C language bit operation