Add Vec3DPool for diff visibility

src/main/java/net/minecraft/server/Vec3DPool.java

@@ -0,0 +1,53 @@
+package net.minecraft.server;
+
+import java.util.ArrayList;
+import java.util.List;
+
+public class Vec3DPool {
+
+    private final int a;
+    private final int b;
+    private final List c = new ArrayList();
+    private int d = 0;
+    private int e = 0;
+    private int f = 0;
+
+    public Vec3DPool(int i, int j) {
+        this.a = i;
+        this.b = j;
+    }
+
+    public Vec3D create(double d0, double d1, double d2) {
+        Vec3D vec3d;
+
+        if (this.d >= this.c.size()) {
+            vec3d = new Vec3D(d0, d1, d2);
+            this.c.add(vec3d);
+        } else {
+            vec3d = (Vec3D) this.c.get(this.d);
+            vec3d.b(d0, d1, d2);
+        }
+
+        ++this.d;
+        return vec3d;
+    }
+
+    public void a() {
+        if (this.d > this.e) {
+            this.e = this.d;
+        }
+
+        if (this.f++ == this.a) {
+            int i = Math.max(this.e, this.c.size() - this.b);
+
+            while (this.c.size() > i) {
+                this.c.remove(i);
+            }
+
+            this.e = 0;
+            this.f = 0;
+        }
+
+        this.d = 0;
+    }
+}