c++ - 确保 float 小于 double C++

Question

这是我想做的:

Take a double (which is between -1 and 1) and cast it to a float. But I want to make sure that the float is ALWAYS less than the double.

有什么简单的方法可以做到这一点吗？

作为引用，这是我想出的一些东西。

float DoubleToSmallerFloat (double X) // ex. X = 0.79828470019999997
{
    float  Y = X; // 0.79828471 -> note this is greater than X

    double Diff = X - Y;
    return Y - Abs (Diff) * 10;
}

Answer 1

如果您能够使用 C++11，那么您可以使用 nextafter()为此:

float doubleToSmallerFloat(double x) {
    float f = x;
    return f < x ? f : nextafter(f, -1.0f);
}