C语言中位操作

一、基本位操作

|	或
&	与
~	取反
^	异或
<<	左移
>>	右移

二、位操作的常见用法

1.获取某位的值

#define BitGet(Number,pos) ((Number)|= 1<<(pos)) //把某位置1
#define BitGet(Number,pos) ((Number) &= ~(1<<(pos)) //把某位置0
#define BitGet(Number,pos) ((Number) >> (pos)&1)) //用宏得到某数的某位
#define BitGet(Number,pos) ((Number) ^= 1<<(pos)) //把Number的POS位取反

2.设定某位的值(设为0或1)

方法一：

#define setbit(x,y) x|=(1<<y) //将x的第y位置1
#define clrbit(x,y) x&=~(1<<y) //将x的第y位清0

方法二：

置0，用0去‘与’

int a|=(1<

置1，用1去‘或’
int a&=~(1<

3.循环移位

#define ROTATE_LEFT(x, n) ((x) << (n)) | ((x) >> ((8 * sizeof(x)) - (n)))
#define ROTATE_RIGHT(x, n) ((x) >> (n)) | ((x) << ((8 * sizeof(x)) - (n)))

4.计算绝对值

int   abs(int x)
{
    int y;
    y = x>>31;
    return (x^y)-y; //or:(x+y)^y
}

 5.判断整数的符号

int sign(int x)
{
    return (x>>31)|(unsigned(-x))>>31;
}

 6.两个数比较

  x==y:         ~(x-y|y-x)
  x!=y:         x-y|y-x
  x<y:             (x-y)^((x^y)&((x-y)^x))
  x<=y:         (x|~y)&((x^y)|~(y-x))
  x<y:          (~x&y)|((~x|y)&(x-y))//无符号x,y比较
  x<=y:         (~x|y)&((x^y)|~(y-x))//无符号x,y比较

7.交换两个数的值(swap)

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

8.位计数

方法一：
int count(long v)
{
    int number = 0;

    while(v)
    {
        v &= (v-1);
        number++;
    }
    return number;
}
方法二：
int   count(unsigned   x)
{
    x   =   x-((x>>1)&0x55555555)   ;
    x   =   (x&0x33333333)+(x>>2)&0x33333333);
    x   =   (x+(x>>4))&0x0f0f0f0f;
    x   =   x+(x>>8);
    x   =   x+(x>>16);
    return   x&0x0000003f;
}

 9.二进制和GRAY码的转换

(1).二进制码到GRAY码的转换:
  unsigned   B2G(unsigned   B   )
  {
      return   B   ^   (B>>1)   ;
  }
  (2).GRAY码到二进制码:
  unsigned   G2B(unsigned   G)
 {
     unsigned   B   ;
     B   =   G   ^   (G>>1)   ;
     B   =   G   ^   (G>>2)   ;
     B   =   G   ^   (G>>4)   ;
     B   =   G   ^   (G>>8)   ;
     B   =   G   ^   (G>>16)   ;
     return   B   ;
  }

10.位反转

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