求绝对值的方法汇总

来源：互联网发布：三菱flrd 数据读出编辑：程序博客网时间：2024/06/04 19:10
void fnTestAbs(){    /** abs库函数的调试版    int __cdecl abs (    int number    )    {    return( number>=0 ? number : -number );    }    */    int iA = -789;    int iB = 789;    float fA = -789;    float fB = 789;    /// 调用库函数实现    fA = fabsf(fA); ///< M$真抠门, 到 fabs 已经没有源码实现了    fB = fabsf(fB);    iA = abs(iA);    iB = abs(iB);    /// 用短路表达式, 实现形式上的无分支    iA = -789;    iB = 789;    iA = absEx1(iA);    iB = absEx1(iB);    /// 1. 真正的无分支方法实现abs    iA = -789;    iB = 789;    iA = absEx2(iA);    iB = absEx2(iB);    /// 2. 真正的无分支方法实现abs    iA = -789;    iB = 789;    iA = absEx3(iA);    iB = absEx3(iB);}int absEx1(int iIn){    (iIn < 0) && (iIn = -iIn);    return iIn;}int absEx2(int iIn){    /// 得到符号位为原始符号代表的值 * 原值    /// 如果符号位为-, 得到-1(0xFFFFFFFF) | 1 = -1    /// 如果符号位为+, 得到0(0x00000000) | 1 = 1    return ((iIn >> 31) | 1) * iIn;}int absEx3(int iIn){    int m = iIn >> 31;    /// 得到符号位组成的int值    /// if (iIn > 0), m = 0;    /// if (iIn < 0), m =  0xffffffff;    iIn = iIn ^ m; ///< 取反    /// if (iIn > 0), iIn = iIn ^ 0 = iIn; 不变    /// if (iIn < 0), iIn = iIn ^ 0xffffffff = ~iIn;    iIn = iIn - m; ///< 加1    /// if (iIn > 0), iIn = iIn - 0 = iIn;    /// if (iIn < 0), iIn = iIn - 0xffffffff = iIn - (-1) = iIn + 1;    /// 负数取反+1, 变成了正数    return iIn;}
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