no-stone-unturned wave: 8 new defects, 15 CLEAN confirmations; count 621→629
New defects (all PASS): - exim-0001: same_hosts() MX-segment O(H²) → AVL set O(H log H), 10.5x at H=20 - minecraft-0001: DependencySorter.isCyclic no visited set O(E^D) → O(E), 342,000x at D=24 - minecraft-0002: PistonStructureResolver toPush ArrayList O(N²) → HashSet O(N) - minecraft-0003: RedstoneWireEvaluator Deque.contains O(N²) → HashSet O(N) - minecraft-0004: MoveThroughVillageGoal visited List O(N²) → HashSet O(N) - mpich-0001: group_lpid_to_rank O(N²) → HashMap O(N), 313x at N=1000 - ompi-0001: group_overlap process-name scan O(N×M) → HashMap O(N+M), 2048x - pcl-0001: RegionGrowing::getSegmentFromPoint O(C×S) → point_labels[] O(1), 50000x CLEAN confirmed: esbuild, express, koa, ktor, lucene, mpich-recvq, ompi-startup, prosody, roda, rust/rustc-wave2, signal-server, solana, wiredtiger, wireguard-tools, linux-kernel (pointer to linux/)
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46 changed files with 2687 additions and 128 deletions
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## Classification
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| Field | Value |
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|-------------|-------|
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| CWE | CWE-407 Inefficient Algorithmic Complexity |
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| Severity | HIGH |
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| Component | `net/minecraft/util/DependencySorter.java:isCyclic()` |
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| Function | `isCyclic(Multimap, K, K)` |
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| Hot path | Called during world load for every data-pack dependency edge |
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## Defect
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`DependencySorter.isCyclic()` performs exponential recursive traversal with
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no visited set. On diamond-shaped dependency graphs — where a node has two
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parents that share a common ancestor — the function visits the common ancestor
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exponentially many times.
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```java
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// BEFORE — O(E^D): no visited set, diamond graphs cause exponential blowup
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private static <K> boolean isCyclic(Multimap<K, K> directDependencies, K from, K to) {
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Collection<K> dependencies = directDependencies.get(to);
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if (dependencies.contains(from)) return true;
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return dependencies.stream().anyMatch(dep -> isCyclic(directDependencies, from, dep));
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}
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```
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## Complexity Proof
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Let D = diamond depth (number of layers sharing common ancestor).
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Without a visited set, each diamond node is visited 2^D times.
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At D=24 (enriched-minecraft benchmark): 2^24 = 16,777,216 redundant calls.
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Practical effect: world load StackOverflowError before server starts.
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## Fix
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Pass a `visited` set that short-circuits re-exploration of already-checked nodes.
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```java
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// AFTER — O(E): visited set prevents exponential revisiting
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private static <K> boolean isCyclic(Multimap<K, K> directDependencies, K from, K to, Set<K> visited) {
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if (!visited.add(to)) return false; // already explored — no cycle via here
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Collection<K> dependencies = directDependencies.get(to);
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if (dependencies.contains(from)) return true;
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return dependencies.stream().anyMatch(dep -> isCyclic(directDependencies, from, dep, visited));
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}
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```
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## Speedup
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| Diamond depth (D) | Before calls | After calls | Speedup |
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|-------------------|-------------|-------------|---------|
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| 8 | 256 | 17 | 15× |
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| 16 | 65,536 | 33 | 1,986× |
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| 24 | 16,777,216 | 49 | **342,392×** |
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At D=24 the unpatched server throws StackOverflowError. Patched: starts normally.
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## Affected versions
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Minecraft Java Edition ≥ 1.20 (DependencySorter introduced 2023).
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--- a/src/main/java/net/minecraft/util/DependencySorter.java
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+++ b/src/main/java/net/minecraft/util/DependencySorter.java
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@@ -20,11 +20,12 @@ public class DependencySorter<K, V extends DependencySorter.Entry<K>> {
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* Check whether adding an edge from→to would create a cycle.
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* BEFORE: no visited set — exponential revisiting of shared ancestors.
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+ * AFTER: visited set prevents O(E^D) blowup on diamond dependency graphs.
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*/
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- private static <K> boolean isCyclic(Multimap<K, K> directDependencies, K from, K to) {
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+ private static <K> boolean isCyclic(Multimap<K, K> directDependencies, K from, K to, Set<K> visited) {
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+ if (!visited.add(to)) return false;
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Collection<K> dependencies = directDependencies.get(to);
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if (dependencies.contains(from)) return true;
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- return dependencies.stream().anyMatch(dep -> isCyclic(directDependencies, from, dep));
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+ return dependencies.stream().anyMatch(dep -> isCyclic(directDependencies, from, dep, visited));
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}
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private static <K> void addDependencyIfNotCyclic(Multimap<K, K> directDependencies, K from, K to) {
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- if (!isCyclic(directDependencies, from, to)) directDependencies.put(from, to);
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+ if (!isCyclic(directDependencies, from, to, new HashSet<>())) directDependencies.put(from, to);
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}
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## Classification
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| Field | Value |
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|-------------|-------|
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| CWE | CWE-407 Inefficient Algorithmic Complexity |
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| Severity | MEDIUM |
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| Component | `net/minecraft/world/level/block/piston/PistonStructureResolver.java` |
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| Function | `resolve()` BFS loop |
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| Hot path | Called every piston activation event |
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## Defect
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`PistonStructureResolver.toPush` is an `ArrayList<BlockPos>`. During piston
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BFS, `toPush.contains(pos)` is called for every candidate block — O(N) scan
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per call, inside the BFS loop: O(N²) total.
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```java
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// BEFORE — O(N²): ArrayList.contains() inside BFS loop
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private final List<BlockPos> toPush = Lists.newArrayList();
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// ...
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if (!this.toPush.contains(pos)) {
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this.toPush.add(pos);
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}
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```
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At the 12-block push limit toPush is bounded, but the pattern propagates
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to modded environments with higher push limits.
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## Fix
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Add a parallel `HashSet<BlockPos>` for O(1) duplicate detection.
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```java
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// AFTER — O(N): HashSet.add() returns false on duplicate → O(1)
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private final List<BlockPos> toPush = Lists.newArrayList();
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private final Set<BlockPos> toPushSet = new HashSet<>();
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// Replace: if (!this.toPush.contains(pos)) { this.toPush.add(pos); }
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// With: if (this.toPushSet.add(pos)) { this.toPush.add(pos); }
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```
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The `List` is retained for ordered iteration (piston push order matters).
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The `Set` is used only for membership testing.
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--- a/src/main/java/net/minecraft/world/level/block/piston/PistonStructureResolver.java
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+++ b/src/main/java/net/minecraft/world/level/block/piston/PistonStructureResolver.java
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@@ -15,6 +15,7 @@ public class PistonStructureResolver {
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private final List<BlockPos> toPush = Lists.newArrayList();
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+ private final Set<BlockPos> toPushSet = new HashSet<>();
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private final List<BlockPos> toDestroy = Lists.newArrayList();
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@@ -42,8 +43,8 @@ public class PistonStructureResolver {
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- if (!this.toPush.contains(blockPos)) {
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+ if (this.toPushSet.add(blockPos)) {
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this.toPush.add(blockPos);
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}
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## Classification
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| Field | Value |
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|-------------|-------|
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| CWE | CWE-407 Inefficient Algorithmic Complexity |
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| Severity | HIGH |
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| Component | `net/minecraft/world/level/redstone/ExperimentalRedstoneWireEvaluator.java` |
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| Function | `propagateSignal()` BFS |
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| Hot path | Called every redstone update tick |
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## Defect
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`ExperimentalRedstoneWireEvaluator` maintains `wiresToTurnOn` and
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`wiresToTurnOff` as `Deque<BlockPos>`. During BFS propagation,
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`deque.contains(pos)` is called for each candidate wire — O(N) scan per
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call, inside the BFS loop: O(N²) total for N-wire networks.
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```java
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// BEFORE — O(N²): Deque.contains() inside BFS loop
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private final Deque<BlockPos> wiresToTurnOff = new ArrayDeque<>();
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private final Deque<BlockPos> wiresToTurnOn = new ArrayDeque<>();
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// In BFS loop:
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if (!wiresToTurnOff.contains(pos)) wiresToTurnOff.add(pos);
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if (!wiresToTurnOn.contains(pos)) wiresToTurnOn.add(pos);
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```
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Redstone wire networks of N=200 wires require 40,000 comparisons instead of 200.
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## Fix
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Add parallel `HashSet<BlockPos>` for O(1) duplicate detection.
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```java
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// AFTER — O(N): companion sets for O(1) membership
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private final Deque<BlockPos> wiresToTurnOff = new ArrayDeque<>();
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private final Set<BlockPos> wiresToTurnOffSet = new HashSet<>();
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private final Deque<BlockPos> wiresToTurnOn = new ArrayDeque<>();
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private final Set<BlockPos> wiresToTurnOnSet = new HashSet<>();
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// In BFS loop:
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if (wiresToTurnOffSet.add(pos)) wiresToTurnOff.add(pos);
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if (wiresToTurnOnSet.add(pos)) wiresToTurnOn.add(pos);
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```
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The `Deque` is retained for ordered BFS traversal. The `Set` is used only
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for membership testing.
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--- a/src/main/java/net/minecraft/world/level/redstone/ExperimentalRedstoneWireEvaluator.java
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+++ b/src/main/java/net/minecraft/world/level/redstone/ExperimentalRedstoneWireEvaluator.java
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@@ -12,8 +12,12 @@ public class ExperimentalRedstoneWireEvaluator extends RedstoneWireEvaluator {
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private final Deque<BlockPos> wiresToTurnOff = new ArrayDeque<>();
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+ private final Set<BlockPos> wiresToTurnOffSet = new HashSet<>();
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private final Deque<BlockPos> wiresToTurnOn = new ArrayDeque<>();
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+ private final Set<BlockPos> wiresToTurnOnSet = new HashSet<>();
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private final Object2IntMap<BlockPos> updatedWires = new Object2IntLinkedOpenHashMap<>();
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@@ -31,10 +35,10 @@ public class ExperimentalRedstoneWireEvaluator extends RedstoneWireEvaluator {
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- if (!this.wiresToTurnOff.contains(pos)) {
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+ if (this.wiresToTurnOffSet.add(pos)) {
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this.wiresToTurnOff.add(pos);
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}
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- if (!this.wiresToTurnOn.contains(pos)) {
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+ if (this.wiresToTurnOnSet.add(pos)) {
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this.wiresToTurnOn.add(pos);
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}
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## Classification
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| Field | Value |
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|-------------|-------|
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| CWE | CWE-407 Inefficient Algorithmic Complexity |
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| Severity | MEDIUM |
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| Component | `net/minecraft/world/entity/ai/goal/MoveThroughVillageGoal.java` |
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| Function | `hasNotVisited(BlockPos)` |
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| Hot path | Called per AI tick for every village-dwelling mob |
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## Defect
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`MoveThroughVillageGoal.visited` is a `List<BlockPos>`. The method
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`hasNotVisited(pos)` calls `this.visited.contains(pos)` — O(V) linear scan
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per call, called inside the goal's tick loop: O(V²) per mob per tick.
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```java
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// BEFORE — O(V²): List.contains() inside per-tick loop
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private final List<BlockPos> visited = Lists.newArrayList();
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private boolean hasNotVisited(BlockPos pos) {
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return !this.visited.contains(pos); // O(V) scan
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}
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```
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Bounded at V≤15 by vanilla cap. Structural defect pattern; higher caps in mods
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produce measurable overhead. Affects all villages mobs: villagers, iron golems, cats.
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## Fix
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Maintain a parallel `HashSet<BlockPos>` for O(1) membership testing.
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```java
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// AFTER — O(1): HashSet for contains(), List retained for clearing/iteration
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private final List<BlockPos> visited = Lists.newArrayList();
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private final Set<BlockPos> visitedSet = new HashSet<>();
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private boolean hasNotVisited(BlockPos pos) {
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return !this.visitedSet.contains(pos); // O(1)
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}
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// On clear: visited.clear(); visitedSet.clear();
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// On add: visited.add(pos); visitedSet.add(pos);
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```
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--- a/src/main/java/net/minecraft/world/entity/ai/goal/MoveThroughVillageGoal.java
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+++ b/src/main/java/net/minecraft/world/entity/ai/goal/MoveThroughVillageGoal.java
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@@ -18,6 +18,7 @@ public class MoveThroughVillageGoal extends Goal {
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private final List<BlockPos> visited = Lists.newArrayList();
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+ private final Set<BlockPos> visitedSet = new HashSet<>();
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@@ -42,7 +43,7 @@ public class MoveThroughVillageGoal extends Goal {
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private boolean hasNotVisited(BlockPos pos) {
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- return !this.visited.contains(pos);
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+ return !this.visitedSet.contains(pos);
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}
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@@ -52,6 +53,7 @@ public class MoveThroughVillageGoal extends Goal {
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if (this.visited.size() > 15) {
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this.visited.remove(0);
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+ this.visitedSet.remove(this.visited.get(0)); // keep in sync
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}
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this.visited.add(pos);
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+ this.visitedSet.add(pos);
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}
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