diff --git a/cc3d.hpp b/cc3d.hpp
index 5fb4d74..d813d3d 100644
--- a/cc3d.hpp
+++ b/cc3d.hpp
@@ -918,36 +918,180 @@ OUT* connected_components2d_4(
   // Raster Scan 1: Set temporary labels and 
   // record equivalences in a disjoint set.
 
+#define NEW_LABEL() \
+  next_label++; \
+  out_labels[loc] = next_label; \
+  equivalences.add(out_labels[loc]);
+
+#define INIT_TREE() \
+    if (++x >= xend - 1) { goto FINAL_TREE; } \
+    loc = x + sx * y; \
+    cur = in_labels[loc]; \
+    next = in_labels[loc + 1];
+
   T cur = 0;
+  T next = 0;
   for (int64_t y = 0; y < sy; y++, row++) {
     const int64_t xstart = runs[row << 1];
     const int64_t xend = runs[(row << 1) + 1];
 
-    for (int64_t x = xstart; x < xend; x++) {
-      loc = x + sx * y;
-      cur = in_labels[loc];
+    int64_t x = xstart - 1;
+    goto NO_B;
 
-      if (cur == 0) {
-        continue;
+    FULLTREE:
+    INIT_TREE()
+    if (cur == 0) { 
+      goto NO_B; 
+    }
+    else if (x > 0 && cur == in_labels[loc + B]) {
+      out_labels[loc + A] = out_labels[loc + B];
+      if (y > 0 && cur == in_labels[loc + C]) {
+        if (cur != in_labels[loc + D]) {
+          equivalences.unify(out_labels[loc + A], out_labels[loc + C]);
+        }
+        if (cur == next) {
+          goto ASSUME_BD;
+        }
+        else {
+          goto NO_B;
+        }
+      }
+      else if (cur == next) {
+        goto NO_D;
+      }
+      else {
+        goto NO_B;
+      }
+    }
+    else if (y > 0 && cur == in_labels[loc + C]) {
+      out_labels[loc + A] = out_labels[loc + C];
+      if (cur == next) {
+        goto ASSUME_BD;
+      }
+      else {
+        goto NO_B;
       }
+    }
+    else {
+      NEW_LABEL()
+      goto NO_D;
+    }
 
-      if (x > 0 && cur == in_labels[loc + B]) {
-        out_labels[loc + A] = out_labels[loc + B];
-        if (y > 0 && cur != in_labels[loc + D] && cur == in_labels[loc + C]) {
-          equivalences.unify(out_labels[loc + A], out_labels[loc + C]);
+    NO_B:
+    INIT_TREE()
+    if (cur == 0) { 
+      goto NO_B; 
+    }
+    else if (y > 0 && cur == in_labels[loc + C]) {
+      out_labels[loc + A] = out_labels[loc + C];
+      if (cur == next) {
+        goto ASSUME_BD;
+      }
+      else {
+        goto NO_B;
+      }
+    }
+    else {
+      NEW_LABEL()
+      goto NO_D;
+    }
+
+    ASSUME_BD:
+    INIT_TREE()
+    if (cur == 0) { 
+      goto NO_B; 
+    }
+    else {
+      out_labels[loc + A] = out_labels[loc + B];
+      if (cur == next) {
+        goto ASSUME_B;
+      }
+      goto NO_B;
+    }
+
+    ASSUME_B:
+    INIT_TREE()
+    out_labels[loc + A] = out_labels[loc + B];
+    if (y > 0 && cur == in_labels[loc + C]) {
+      if (cur != in_labels[loc + D]) {
+        equivalences.unify(out_labels[loc + A], out_labels[loc + C]);
+      }
+      if (cur == next) {
+        goto ASSUME_BD;
+      }
+      else {
+        goto NO_B;
+      }
+    }
+    else if (cur == next) {
+      goto NO_D;
+    }
+    else {
+      goto NO_B;
+    }
+
+    NO_D:
+    INIT_TREE()
+    if (cur == 0) { 
+      goto NO_B; 
+    }
+    else if (x > 0 && cur == in_labels[loc + B]) {
+      out_labels[loc + A] = out_labels[loc + B];
+      if (y > 0 && cur == in_labels[loc + C]) {
+        equivalences.unify(out_labels[loc + A], out_labels[loc + C]);
+        if (cur == next) {
+          goto ASSUME_BD;
+        }
+        else {
+          goto NO_B;
         }
       }
-      else if (y > 0 && cur == in_labels[loc + C]) {
-        out_labels[loc + A] = out_labels[loc + C];
+      else if (cur == next) {
+        goto NO_D;
       }
       else {
-        next_label++;
-        out_labels[loc + A] = next_label;
-        equivalences.add(out_labels[loc + A]);
+        goto NO_B;
+      }
+    }
+    else if (y > 0 && cur == in_labels[loc + C]) {
+      out_labels[loc + A] = out_labels[loc + C];
+      if (cur == next) {
+        goto ASSUME_BD;
+      }
+      else {
+        goto NO_B;
+      }
+    }
+    else {
+      NEW_LABEL()
+      goto NO_D;
+    }
+
+    FINAL_TREE:
+    if (x >= xend) { continue; }
+    loc = x + sx * y;
+    cur = in_labels[loc];
+
+    if (cur == 0) {
+      continue;
+    }
+    else if (x > 0 && cur == in_labels[loc + B]) {
+      out_labels[loc + A] = out_labels[loc + B];
+      if (y > 0 && cur != in_labels[loc + D] && cur == in_labels[loc + C]) {
+        equivalences.unify(out_labels[loc + A], out_labels[loc + C]);
       }
     }
+    else if (y > 0 && cur == in_labels[loc + C]) {
+      out_labels[loc + A] = out_labels[loc + C];
+    }
+    else {
+      NEW_LABEL()
+    }
   }
 
+#undef NEW_LABEL
+#undef INIT_TREE
+
   out_labels = relabel<OUT>(out_labels, sx, sy, /*sz=*/1, next_label, equivalences, N, runs);
   delete[] runs;
   return out_labels;
diff --git a/test.cpp b/test.cpp
index 677b386..b00e59e 100644
--- a/test.cpp
+++ b/test.cpp
@@ -39,10 +39,7 @@ uint32_t* read_subvol() {
   return input;
 }
 
-uint32_t* randomvol() {
-	size_t sx = 512;
-	size_t sy = 512;
-	size_t sz = 512;
+uint32_t* randomvol(size_t sx = 512, size_t sy = 512, size_t sz = 512) {
 	size_t voxels = sx * sy * sz;
 
 	uint32_t *big = new uint32_t[sx*sy*sz]();
@@ -52,23 +49,18 @@ uint32_t* randomvol() {
 	return big;
 }
 
-uint32_t* black() {
-	size_t sx = 512;
-	size_t sy = 512;
-	size_t sz = 512;
-	size_t voxels = sx * sy * sz;
-
+uint32_t* black(size_t sx = 512, size_t sy = 512, size_t sz = 512) {
 	return new uint32_t[sx*sy*sz]();
 }
 
 int main () {
 
-	size_t sx = 512;
-	size_t sy = 512;
-	size_t sz = 512;
+	size_t sx = 10000;
+	size_t sy = 10000;
+	size_t sz = 1;
 	size_t voxels = sx * sy * sz;
 
-	uint32_t* subvol = black();
+	uint32_t* subvol = randomvol(sx,sy,sz);
 
   typedef std::chrono::high_resolution_clock Time;
   typedef std::chrono::milliseconds ms;
@@ -76,7 +68,7 @@ int main () {
   auto t0 = Time::now();
   int N = 1;
   for (int i = 0; i < N; i++) {
-		cc3d::connected_components3d<uint32_t, uint32_t>(subvol, sx,sy,sz, 26);
+		cc3d::connected_components3d<uint32_t, uint32_t>(subvol, sx,sy,sz, 4);
 	}
 
   auto t1 = Time::now();