常用位操作的c++实现

Posted 2022-11-30 周旭光

看到这个标题，可能大家会误解，其实就是贡献几个比较实用的运用位运算实现的操作，这对于加快程序的运行速度很有帮助。具体的实现是参考

http://graphics.stanford.edu/~seander/bithacks.html实现的。

   下面给出其函数声明及其实现。

    

//判断该整数是否是2的整数次方
bool IsPowerOfTwo (unsigned int value);
bool IsPowerOfTwo (int value);

//求以2为底的结果
unsigned int Log2OfPowerOfTwo (unsigned int powerOfTwo);
int Log2OfPowerOfTwo (int powerOfTwo);

//判断两个数是否异号
bool IsOppositeSigns(int value1,int value2);

//不使用分支计算绝对值
unsigned int GetAbs(int value);

//大于等于value的最近的二的次方的数
unsigned int NextPowerOfTwo(unsigned int value);

//实现
bool IsPowerOfTwo (unsigned int value)

    return (value > 0) && ((value & (value - 1)) == 0);


bool IsPowerOfTwo (int value)

    return (value > 0) && ((value & (value - 1)) == 0);


unsigned int Log2OfPowerOfTwo (unsigned int powerOfTwo)

    unsigned int log2 = (powerOfTwo & 0xAAAAAAAA) != 0;
    log2 |= ((powerOfTwo & 0xFFFF0000) != 0) << 4;
    log2 |= ((powerOfTwo & 0xFF00FF00) != 0) << 3;
    log2 |= ((powerOfTwo & 0xF0F0F0F0) != 0) << 2;
    log2 |= ((powerOfTwo & 0xCCCCCCCC) != 0) << 1;
    return log2;


int Log2OfPowerOfTwo (int powerOfTwo)

    unsigned int log2 = (powerOfTwo & 0xAAAAAAAA) != 0;
    log2 |= ((powerOfTwo & 0xFFFF0000) != 0) << 4;
    log2 |= ((powerOfTwo & 0xFF00FF00) != 0) << 3;
    log2 |= ((powerOfTwo & 0xF0F0F0F0) != 0) << 2;
    log2 |= ((powerOfTwo & 0xCCCCCCCC) != 0) << 1;
    return (int)log2;


bool IsOppositeSigns(int value1,int value2)

    return (value1 ^ value2) < 0;


unsigned int GetAbs(int value)

    unsigned int r;  // the result goes here
    int const mask = value >> (sizeof(int) * CHAR_BIT - 1);
    
    //r = (value + mask) ^ mask;
    //Patented variation:
    r = (value ^ mask) - mask;
    return r;


unsigned int NextPowerOfTwo(unsigned int value)

    value--;
    value |= value >> 1;
    value |= value >> 2;
    value |= value >> 4;
    value |= value >> 8;
    value |= value >> 16;
    value++;
    
    return value;

希望对大家有用