Cannot sample enough valid points. (more)

\[\left(\left(\left(\sqrt{x + 1.0} - \sqrt{x}\right) + \left(\sqrt{y + 1.0} - \sqrt{y}\right)\right) + \left(\sqrt{z + 1.0} - \sqrt{z}\right)\right) + \left(\sqrt{t + 1.0} - \sqrt{t}\right)\]
\left(\left(\left(\sqrt{x + 1.0} - \sqrt{x}\right) + \left(\sqrt{y + 1.0} - \sqrt{y}\right)\right) + \left(\sqrt{z + 1.0} - \sqrt{z}\right)\right) + \left(\sqrt{t + 1.0} - \sqrt{t}\right)
double f(double x, double y, double z, double t) {
        double r15891380 = x;
        double r15891381 = 1.0;
        double r15891382 = r15891380 + r15891381;
        double r15891383 = sqrt(r15891382);
        double r15891384 = sqrt(r15891380);
        double r15891385 = r15891383 - r15891384;
        double r15891386 = y;
        double r15891387 = r15891386 + r15891381;
        double r15891388 = sqrt(r15891387);
        double r15891389 = sqrt(r15891386);
        double r15891390 = r15891388 - r15891389;
        double r15891391 = r15891385 + r15891390;
        double r15891392 = z;
        double r15891393 = r15891392 + r15891381;
        double r15891394 = sqrt(r15891393);
        double r15891395 = sqrt(r15891392);
        double r15891396 = r15891394 - r15891395;
        double r15891397 = r15891391 + r15891396;
        double r15891398 = t;
        double r15891399 = r15891398 + r15891381;
        double r15891400 = sqrt(r15891399);
        double r15891401 = sqrt(r15891398);
        double r15891402 = r15891400 - r15891401;
        double r15891403 = r15891397 + r15891402;
        return r15891403;
}