Minor improvement

Add a trivial check to H48 solver. The benchmarks show, surprisingly,
a more noticeable improvement for larger solvers (h10, h11). I was expecting
it to be more noticeable for smaller solvers.

It is likely that this change is irrelevant to performance and all changes
in the benchmark results are just random chance.

2 files changed, 31 insertions, 26 deletions

diff --git a/benchmarks/results_h48.py b/benchmarks/results_h48.py
index a2db06c..9d8d19c 100644
--- a/benchmarks/results_h48.py
+++ b/benchmarks/results_h48.py
@@ -1,36 +1,36 @@
 h48_single_thread = {
-        6: {17: 52.7302, 18: 405.7879, 19: 2032.4602},
-        7: {17: 26.4977, 18: 212.7314, 19: 1074.2251},
-        8: {17: 19.8239, 18: 151.7597, 19: 639.6197},
-        9: {17: 9.0082, 18: 62.0400, 19: 293.2197},
-        10: {17: 6.2190, 18: 31.1395, 19: 158.3581, 20: 1118.7513, "superflip": 48.7016},
-        11: {17: 3.5879, 18: 19.5970, 19: 93.5762, 20: 651.2212, "superflip": 20.2721},
+        6: {17: 52.9727, 18: 407.1435, 19: 2055.8785},
+        7: {17: 26.8541, 18: 214.7064, 19: 1053.9732},
+        8: {17: 19.8408, 18: 152.2214, 19: 639.4834},
+        9: {17: 8.9053, 18: 61.6760, 19: 294.6517},
+        10: {17: 5.8445, 18: 30.0880, 19: 154.5389, 20: 1087.6552, "superflip": 48.8410},
+        11: {17: 3.2420, 18: 18.3482, 19: 85.6898, 20: 581.9588, "superflip": 19.2614},
 }
 
 h48_4_threads = {
-        6: {17: 15.2794, 18: 116.1387, 19: 577.3595},
-        7: {17: 7.7522, 18: 59.8914, 19: 293.4824},
-        8: {17: 5.8807, 18: 42.7619, 19: 180.4499},
-        9: {17: 2.7609, 18: 18.4867, 19: 84.1350, 20: 610.8914, "superflip": 25.3932},
-        10: {17: 1.9215, 18: 9.1287, 19: 43.7573, 20: 338.4877, "superflip": 14.2593},
-        11: {17: 1.1997, 18: 5.8332, 19: 26.6060, 20: 176.8453, "superflip": 6.1932},
+        6: {17: 15.2251, 18: 115.3688, 19: 605.5267},
+        7: {17: 7.8799, 18: 61.3355, 19: 303.0388},
+        8: {17: 5.8624, 18: 43.4193, 19: 179.8491},
+        9: {17: 2.7696, 18: 17.6190, 19: 87.1236, 20: 640.3405, "superflip": 25.3726},
+        10: {17: 1.8676, 18: 9.0543, 19: 44.7847, 20: 310.3914, "superflip": 14.0333},
+        11: {17: 1.1173, 18: 5.6240, 19: 24.1467, 20: 174.4689, "superflip": 5.9548},
 }
 
 h48_16_threads = {
-        6: {17: 5.3639, 18: 37.6695, 19: 191.8620},
-        7: {17: 2.8213, 18: 20.1045, 19: 96.7922},
-        8: {17: 2.0779, 18: 14.6013, 19: 60.4149},
-        9: {17: 1.0796, 18: 6.1831, 19: 27.5530, 20: 200.9519, "superflip": 10.7149},
-        10: {17: 0.7511, 18: 3.2061, 19: 15.0046, 20: 103.8125, "superflip": 5.6217},
-        11: {17: 0.5173, 18: 2.1196, 19: 8.6965, 20: 56.4344, "superflip": 2.4857},
+        6: {17: 5.3309, 18: 37.8142, 19: 193.5352},
+        7: {17: 2.8657, 18: 20.8215, 19: 99.9139},
+        8: {17: 2.0775, 18: 14.2672, 19: 60.0995},
+        9: {17: 1.0595, 18: 6.2074, 19: 27.5523, 20: 201.2200, "superflip": 10.7739},
+        10: {17: 0.7600, 18: 3.1980, 19: 14.5771, 20: 105.1686, "superflip": 5.5616},
+        11: {17: 0.4946, 18: 2.0381, 19: 8.3613, 20: 55.4269, "superflip": 2.4087},
 }
 
 h48_all_solutions = {
-        6: {17: 17.1940, 18: 203.6879, 19: 2286.7364},
-        7: {17: 9.0219, 18: 105.0559, 19: 1166.1059},
-        8: {17: 5.9919, 18: 68.8215, 19: 686.0935},
-        9: {17: 3.0192, 18: 31.9398, 19: 319.0297},
-        10: {17: 1.7972, 18: 17.8931, 19: 167.6695, 20: 1464.2636, "superflip": 48.9035},
-        11: {17: 1.1838, 18: 10.5628, 19: 96.0518, 20: 808.8516, "superflip": 22.6335},
+        6: {17: 17.1587, 18: 204.6182, 19: 2296.3135},
+        7: {17: 9.1380, 18: 106.0127, 19: 1177.4728},
+        8: {17: 6.1641, 18: 67.9895, 19: 685.6033},
+        9: {17: 3.0422, 18: 31.9821, 19: 323.2516},
+        10: {17: 1.7822, 18: 17.4947, 19: 168.2516, 20: 1465.2950, "superflip": 48.6248},
+        11: {17: 1.1364, 18: 10.2076, 19: 92.3419, 20: 791.1480, "superflip": 21.8014},
 }
 
diff --git a/src/solvers/h48/solve.h b/src/solvers/h48/solve.h
index 2920fa7..4aa3799 100644
--- a/src/solvers/h48/solve.h
+++ b/src/solvers/h48/solve.h
@@ -115,10 +115,15 @@ solve_h48_stop(dfsarg_solve_h48_t arg[static 1])
         arg->movemask_normal = arg->movemask_inverse = MM18_ALLMOVES;
         arg->nodes_visited++;
 
-        /* Preliminary probing using last computed bound, if possible */
-
         n = arg->solution_moves->nmoves + arg->solution_moves->npremoves;
         target = arg->target_depth - n;
+
+        /* We'll never get a bound higher than base + 3 */
+        if (arg->base + 3 <= target)
+                return false;
+
+        /* Preliminary probing using last computed bound, if possible */
+
         if ((arg->use_lb_normal && arg->lb_normal > target) ||
             (arg->use_lb_inverse && arg->lb_inverse > target))
                 return true;