diff --git a/drama/src/rev-mc.c b/drama/src/rev-mc.c
index ed00035..9ac0afa 100644
--- a/drama/src/rev-mc.c
+++ b/drama/src/rev-mc.c
@@ -340,6 +340,35 @@ find_row_mask(std::vector<set_t> &sets,
     // step /= thread_num;
     // if (!step) { ++step; }
     fprintf(stderr, "worker_step: %ld\n", outer_step);
+    auto try_update_row_mask = [&](uint64_t pos, uint64_t mask) {
+        if (pos > g_base_pos.load(std::memory_order_relaxed)) {
+            std::lock_guard<std::mutex> _(lock);
+            if (pos > g_base_pos.load()) {
+                g_base_pos = row_mask;
+                row_mask   = mask;
+            }
+        }
+    };
+    auto try_get_row_mask = [&](uint64_t end_pos, uint64_t &diff, uint64_t &cur_mask) {
+        uint64_t v = g_base_pos.load(std::memory_order_relaxed);
+        if (end_pos - diff < v && end_pos >= v) {
+            std::lock_guard<std::mutex> _(lock);
+            v = g_base_pos.load();
+            if (end_pos - diff < v && end_pos >= v) {
+                diff     = end_pos - v;
+                cur_mask = row_mask;
+            }
+        }
+    };
+
+    auto set_found = [&](uint64_t cur_mask) {
+        bool expected = false;
+        if (found.compare_exchange_strong(expected, true)) {
+            std::lock_guard<std::mutex> _(lock);
+            found.store(true);
+            row_mask = cur_mask;
+        }
+    };
 
     std::atomic<uint64_t> cnt{0};
     std::atomic<uint64_t> progress{0};
@@ -361,32 +390,12 @@ find_row_mask(std::vector<set_t> &sets,
                         cur_mask = next_bit_permutation(cur_mask);
                     }
                     diff -= std::min(inner_step, diff);
-
-                    if (end_pos - diff > g_base_pos) {
-                        std::lock_guard<std::mutex> _(lock);
-                        if (found) { break; }
-                        if (end_pos - diff > g_base_pos) {
-                            g_base_pos = end_pos - diff;
-                            row_mask   = cur_mask;
-                        }
-                    } else if (end_pos >= g_base_pos) {
-                        std::lock_guard<std::mutex> _(lock);
-                        if (end_pos >= g_base_pos) {
-                            diff     = end_pos - g_base_pos;
-                            cur_mask = row_mask;
-                        }
-                    }
+                    try_update_row_mask(end_pos - diff, cur_mask);
+                    try_get_row_mask(end_pos, diff, cur_mask);
                 }
 
                 for (int i = outer_step; i > 0 && cur_mask < last_mask; --i) {
-                    if (resolve(cur_mask) && !found) {
-                        bool expected = false;
-                        if (found.compare_exchange_strong(expected, true)) {
-                            std::lock_guard<std::mutex> _(lock);
-                            found.store(true);
-                            row_mask = cur_mask;
-                        }
-                    }
+                    if (resolve(cur_mask)) { set_found(cur_mask); }
                     cur_mask = next_bit_permutation(cur_mask);
                 }
             }