1 files changed, 23 insertions, 10 deletions

diff --git a/src/steps.c b/src/steps.c
index 34ddcc2..6478bc2 100644
--- a/src/steps.c
+++ b/src/steps.c
@@ -979,29 +979,42 @@ static int
 estimate_optimal_HTM(CubeTarget ct)
 {
         int dr1, dr2, dr3, cor, ret;
-        Cube cube = ct.cube;
+        Cube inv;
 
-        dr1 = ptableval(&pd_khuge_HTM, cube);
+        dr1 = ptableval(&pd_khuge_HTM, ct.cube);
         cor = estimate_corners_HTM(ct);
         ret = MAX(dr1, cor);
-
         if (ret > ct.target)
                 return ret;
 
-        cube = apply_trans(rf, ct.cube);
-        dr2 = ptableval(&pd_khuge_HTM, cube);
+        dr2 = ptableval(&pd_khuge_HTM, apply_trans(rf, ct.cube));
         ret = MAX(ret, dr2);
-
         if (ret > ct.target)
                 return ret;
 
-        cube = apply_trans(fd, ct.cube);
-        dr3 = ptableval(&pd_khuge_HTM, cube);
-
-        /* Michiel de Bondt's trick */
+        dr3 = ptableval(&pd_khuge_HTM, apply_trans(fd, ct.cube));
         if (dr1 == dr2 && dr2 == dr3 && dr1 != 0)
                 dr3++;
+        ret = MAX(ret, dr3);
+        if (ret > ct.target || ret == 0)
+                return ret;
 
+        /* Inverse cube probing */
+
+        inv = inverse_cube(ct.cube);
+        dr1 = ptableval(&pd_khuge_HTM, inv);
+        ret = MAX(ret, dr1);
+        if (ret > ct.target)
+                return ret;
+
+        dr2 = ptableval(&pd_khuge_HTM, apply_trans(rf, inv));
+        ret = MAX(ret, dr2);
+        if (ret > ct.target)
+                return ret;
+        
+        dr3 = ptableval(&pd_khuge_HTM, apply_trans(fd, inv));
+        if (dr1 == dr2 && dr2 == dr3 && dr1 != 0)
+                dr3++;
         return MAX(ret, dr3);
 }