Cannot sample enough valid points. (more)

\[\left(\left(\left(\sqrt{x + 1} - \sqrt{x}\right) + \left(\sqrt{y + 1} - \sqrt{y}\right)\right) + \left(\sqrt{z + 1} - \sqrt{z}\right)\right) + \left(\sqrt{t + 1} - \sqrt{t}\right)\]
\left(\left(\left(\sqrt{x + 1} - \sqrt{x}\right) + \left(\sqrt{y + 1} - \sqrt{y}\right)\right) + \left(\sqrt{z + 1} - \sqrt{z}\right)\right) + \left(\sqrt{t + 1} - \sqrt{t}\right)
double f(double x, double y, double z, double t) {
        double r8919 = x;
        double r8920 = 1.0;
        double r8921 = r8919 + r8920;
        double r8922 = sqrt(r8921);
        double r8923 = sqrt(r8919);
        double r8924 = r8922 - r8923;
        double r8925 = y;
        double r8926 = r8925 + r8920;
        double r8927 = sqrt(r8926);
        double r8928 = sqrt(r8925);
        double r8929 = r8927 - r8928;
        double r8930 = r8924 + r8929;
        double r8931 = z;
        double r8932 = r8931 + r8920;
        double r8933 = sqrt(r8932);
        double r8934 = sqrt(r8931);
        double r8935 = r8933 - r8934;
        double r8936 = r8930 + r8935;
        double r8937 = t;
        double r8938 = r8937 + r8920;
        double r8939 = sqrt(r8938);
        double r8940 = sqrt(r8937);
        double r8941 = r8939 - r8940;
        double r8942 = r8936 + r8941;
        return r8942;
}