常用位操作的c++实现

来源：互联网发布：淘宝网衣服女装编辑：程序博客网时间：2024/06/15 11:48

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

0 0