regress: provide function to find median

regress.c

@@ -429,6 +429,19 @@ find_median(double *x, int n)
   }
 }
 
+/* ================================================== */
+
+double
+RGR_FindMedian(double *x, int n)
+{
+  double tmp[MAX_POINTS];
+
+  assert(n > 0 && n <= MAX_POINTS);
+  memcpy(tmp, x, n * sizeof (tmp[0]));
+
+  return find_median(tmp, n);
+}
+
 /* ================================================== */
 /* This function evaluates the equation