memory prefetching (#4224)

src/main/cpp/net/eagle0/shardok/library/action_point_distances/ActionPointDistances.cpp

@@ -140,8 +140,13 @@ void ActionPointDistances::PopulateOne(
         const Coords& currentCoords = indexToCoords[currentIndex];
         visited[currentIndex] = true;
 
-        for (const std::array<int, 6>& neighbors = adjacencyTable[currentIndex];
-             int adjacentIndex : neighbors) {
+        // Prefetch terrain data for all neighbors to reduce memory stalls
+        const std::array<int, 6>& neighbors = adjacencyTable[currentIndex];
+        for (int i = 0; i < 6 && neighbors[i] != -1; i++) {
+            __builtin_prefetch(hexMap->terrain()->Get(neighbors[i]), 0, 3);
+        }
+
+        for (int adjacentIndex : neighbors) {
             if (adjacentIndex == -1) break;  // End of valid neighbors
             if (visited[adjacentIndex]) continue;
 
@@ -168,6 +173,11 @@ void ActionPointDistances::PopulateOne(
                         return from.from == currentCoords;
                     });
             if (entry != braveWaterPossibleCoords->details.end()) {
+                // Prefetch terrain data for water braving targets
+                for (const auto braveIndex : entry->to.indexIterator()) {
+                    __builtin_prefetch(hexMap->terrain()->Get(braveIndex), 0, 3);
+                }
+
                 for (const auto braveIndex : entry->to.indexIterator()) {
                     if (visited[braveIndex]) continue;