+static double
+calc_percentile (double p, double valid_cases, double x1, double x2)
+{
+ double s, dummy;
+
+ s = (settings_get_algorithm () != COMPATIBLE
+ ? modf ((valid_cases - 1) * p, &dummy)
+ : modf ((valid_cases + 1) * p - 1, &dummy));
+
+ return x1 + (x2 - x1) * s;
+}
+
+/* Calculates all of the percentiles for VF within FRQ. */