根据平台,C#舍入不同？

Question

我有这么小的代码

double s = -2.6114289999999998;
double s7 = Math.Round(s, 7);
double s5 = Math.Round(s, 5);
double s6 = Math.Round(s, 6);

有了Platform = Any CPU,我明白了

s7: -2.611429   
s5: -2.61143    
s6: -2.611429   

使用Platform = x64,我得到了

s7: -2.6114289999999998 
s5: -2.61143    
s6: -2.6114289999999998

为什么？(从VS的Locals窗口复制的输出)

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整段代码是:

    private void btnAlign_Click(object sender, EventArgs e)
    {
        double s = -2.6114289999999998;
        double s7 = Math.Round(s, 7);
        double s5 = Math.Round(s, 5);
        double s6 = Math.Round(s, 6);
    }

Answer 1

该值-2.611429无法使用 64 位浮点表示。在 32 位模式下编译时，该值将改为使用 80 位（扩展精度）。