diff --git a/overviewer_core/src/block_class.c b/overviewer_core/src/block_class.c
new file mode 100644
index 0000000..47b0e63
--- /dev/null
+++ b/overviewer_core/src/block_class.c
@@ -0,0 +1,136 @@
+/* 
+ * This file is part of the Minecraft Overviewer.
+ *
+ * Minecraft Overviewer is free software: you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License as published
+ * by the Free Software Foundation, either version 3 of the License, or (at
+ * your option) any later version.
+ *
+ * Minecraft Overviewer is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General
+ * Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License along
+ * with the Overviewer.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#include "block_class.h"
+#include "utils.h"
+
+
+bool block_class_is_subset(
+	mc_block_t block,
+	const mc_block_t block_class[],
+	size_t     block_class_len
+)
+{
+	size_t i;
+	for( i = 0; i < block_class_len; ++i )
+	{
+		if( block == block_class[i] )
+		{
+			return true;
+		}
+	}
+	return false;
+}
+
+
+const mc_block_t block_class_stair[] = {
+	block_oak_stairs,
+	block_stone_stairs,
+	block_brick_stairs,
+	block_stone_brick_stairs,
+	block_nether_brick_stairs,
+	block_sandstone_stairs,
+	block_spruce_stairs,
+	block_birch_stairs,
+	block_jungle_stairs,
+	block_quartz_stairs,
+	block_acacia_stairs,
+	block_dark_oak_stairs,
+	block_red_sandstone_stairs,
+	block_purpur_stairs
+};
+const size_t block_class_stair_len = count_of(block_class_stair);
+
+const mc_block_t block_class_door[] = {
+	block_wooden_door,
+	block_iron_door,
+	block_spruce_door,
+	block_birch_door,
+	block_jungle_door,
+	block_acacia_door,
+	block_dark_oak_door
+};
+const size_t block_class_door_len = count_of(block_class_door);
+
+const mc_block_t block_class_fence[] = {
+	block_fence,
+	block_nether_brick_fence,
+	block_spruce_fence,
+	block_birch_fence,
+	block_jungle_fence,
+	block_dark_oak_fence,
+	block_acacia_fence
+};
+const size_t block_class_fence_len = count_of(block_class_fence);
+
+const mc_block_t block_class_fence_gate[] = {
+	block_fence_gate,
+	block_spruce_fence_gate,
+	block_birch_fence_gate,
+	block_jungle_fence_gate,
+	block_dark_oak_fence_gate,
+	block_acacia_fence_gate
+};
+const size_t block_class_fence_gate_len = count_of(block_class_fence_gate);
+
+const mc_block_t block_class_ancil[] = {
+	block_wooden_door,
+	block_iron_door,
+	block_spruce_door,
+	block_birch_door,
+	block_jungle_door,
+	block_acacia_door,
+	block_dark_oak_door,
+	block_oak_stairs,
+	block_stone_stairs,
+	block_brick_stairs,
+	block_stone_brick_stairs,
+	block_nether_brick_stairs,
+	block_sandstone_stairs,
+	block_spruce_stairs,
+	block_birch_stairs,
+	block_jungle_stairs,
+	block_quartz_stairs,
+	block_acacia_stairs,
+	block_dark_oak_stairs,
+	block_red_sandstone_stairs,
+	block_purpur_stairs,
+	block_grass,
+	block_flowing_water,
+	block_water,
+	block_glass,
+	block_chest,
+	block_redstone_wire,
+	block_ice,
+	block_fence,
+	block_portal,
+	block_iron_bars,
+	block_glass_pane,
+	block_waterlily,
+	block_nether_brick_fence,
+	block_cobblestone_wall,
+	block_double_plant,
+	block_stained_glass_pane,
+	block_stained_glass,
+	block_trapped_chest,
+	block_spruce_fence,
+	block_birch_fence,
+	block_jungle_fence,
+	block_dark_oak_fence,
+	block_acacia_fence
+};
+const size_t block_class_ancil_len = count_of(block_class_ancil);
\ No newline at end of file
diff --git a/overviewer_core/src/block_class.h b/overviewer_core/src/block_class.h
new file mode 100644
index 0000000..b772035
--- /dev/null
+++ b/overviewer_core/src/block_class.h
@@ -0,0 +1,47 @@
+/* 
+ * This file is part of the Minecraft Overviewer.
+ *
+ * Minecraft Overviewer is free software: you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License as published
+ * by the Free Software Foundation, either version 3 of the License, or (at
+ * your option) any later version.
+ *
+ * Minecraft Overviewer is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General
+ * Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License along
+ * with the Overviewer.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#ifndef __BLOCK_CLASS_H_INCLUDED__
+#define __BLOCK_CLASS_H_INCLUDED__
+
+#include <stdbool.h>
+#include <stddef.h>
+
+#include "mc_id.h"
+
+bool block_class_is_subset(
+	mc_block_t block,
+	const mc_block_t block_class[],
+	size_t     block_class_len
+);
+
+extern const mc_block_t block_class_stair[];
+extern const size_t     block_class_stair_len;
+
+extern const mc_block_t block_class_door[];
+extern const size_t     block_class_door_len;
+
+extern const mc_block_t block_class_fence[];
+extern const size_t     block_class_fence_len;
+
+extern const mc_block_t block_class_fence_gate[];
+extern const size_t     block_class_fence_gate_len;
+
+extern const mc_block_t block_class_ancil[];
+extern const size_t     block_class_ancil_len;
+
+#endif
\ No newline at end of file
diff --git a/overviewer_core/src/iterate.c b/overviewer_core/src/iterate.c
index 00a6ace..4af96e5 100644
--- a/overviewer_core/src/iterate.c
+++ b/overviewer_core/src/iterate.c
@@ -17,6 +17,7 @@
 
 #include "overviewer.h"
 #include "mc_id.h"
+#include "block_class.h"
 
 static PyObject *textures = NULL;
 
@@ -244,32 +245,6 @@ check_adjacent_blocks(RenderState *state, int x,int y,int z, unsigned short bloc
     return pdata;
 }
 
-
-static int
-is_stairs(int block) {
-    /*
-     * Determines if a block is stairs of any material
-     */
-    switch (block) {
-        case block_oak_stairs:
-        case block_stone_stairs:
-        case block_brick_stairs:
-        case block_stone_brick_stairs:
-        case block_nether_brick_stairs:
-        case block_sandstone_stairs:
-        case block_spruce_stairs:
-        case block_birch_stairs:
-        case block_jungle_stairs:
-        case block_quartz_stairs:
-        case block_acacia_stairs:
-        case block_dark_oak_stairs:
-        case block_red_sandstone_stairs:
-        case block_purpur_stairs:
-            return 1;
-    }
-    return 0;
-}
-
 unsigned short
 generate_pseudo_data(RenderState *state, unsigned short ancilData) {
     /*
@@ -302,8 +277,7 @@ generate_pseudo_data(RenderState *state, unsigned short ancilData) {
         }
         data = (check_adjacent_blocks(state, x, y, z, state->block) ^ 0x0f) | data;
         return (data << 4) | (ancilData & 0x0f);
-    } else if ((state->block == block_fence) || (state->block == block_spruce_fence) || (state->block == block_birch_fence) ||
-            (state->block == block_jungle_fence) || (state->block == block_dark_oak_fence) || (state->block == block_acacia_fence)) { /* fences */
+    } else if (block_class_is_subset(state->block,block_class_fence,block_class_fence_len)) { /* fences */
         /* check for fences AND fence gates */
         return check_adjacent_blocks(state, x, y, z, state->block) | check_adjacent_blocks(state, x, y, z, block_fence_gate) |
                 check_adjacent_blocks(state, x, y, z, block_fence_gate) | check_adjacent_blocks(state, x, y, z, block_birch_fence_gate) | check_adjacent_blocks(state, x, y, z, block_jungle_fence_gate) |
@@ -393,9 +367,7 @@ generate_pseudo_data(RenderState *state, unsigned short ancilData) {
         /* portal and nether brick fences */
         return check_adjacent_blocks(state, x, y, z, state->block);
 
-    } else if ((state->block == block_wooden_door) || (state->block == block_iron_door) || (state->block == block_spruce_door) ||
-            (state->block == block_birch_door) || (state->block == block_jungle_door) || (state->block == block_acacia_door) ||
-            (state->block == block_dark_oak_door)) {
+    } else if (block_class_is_subset(state->block,block_class_door,block_class_door_len)) {
         /* use bottom block data format plus one bit for top/down
          * block (0x8) and one bit for hinge position (0x10)
          */
@@ -442,7 +414,7 @@ generate_pseudo_data(RenderState *state, unsigned short ancilData) {
         pr = pr * pr * 42317861 + pr * 11;
         rotation = 3 & (pr >> 16);
         return rotation;
-    } else if (is_stairs(state->block)) { /* stairs */
+    } else if (block_class_is_subset(state->block,block_class_stair,block_class_stair_len)) { /* stairs */
         /* 4 ancillary bits will be added to indicate which quarters of the block contain the 
          * upper step. Regular stairs will have 2 bits set & corner stairs will have 1 or 3.
          *     Southwest quarter is part of the upper step - 0x40
@@ -499,10 +471,10 @@ generate_pseudo_data(RenderState *state, unsigned short ancilData) {
 
         /* get block & data for neighbors in this order: east, north, west, south */
         /* so we can rotate things easily */
-        stairs[0] = stairs[4] = is_stairs(get_data(state, BLOCKS, x+1, y, z));
-        stairs[1] = stairs[5] = is_stairs(get_data(state, BLOCKS, x, y, z-1));
-        stairs[2] = stairs[6] = is_stairs(get_data(state, BLOCKS, x-1, y, z));
-        stairs[3] = stairs[7] = is_stairs(get_data(state, BLOCKS, x, y, z+1));
+        stairs[0] = stairs[4] = block_class_is_subset(get_data(state, BLOCKS, x+1, y, z),block_class_stair,block_class_stair_len);
+        stairs[1] = stairs[5] = block_class_is_subset(get_data(state, BLOCKS, x, y, z-1),block_class_stair,block_class_stair_len);
+        stairs[2] = stairs[6] = block_class_is_subset(get_data(state, BLOCKS, x-1, y, z),block_class_stair,block_class_stair_len);
+        stairs[3] = stairs[7] = block_class_is_subset(get_data(state, BLOCKS, x, y, z+1),block_class_stair,block_class_stair_len);
         neigh[0] = neigh[4] = FIX_ROT(get_data(state, DATA, x+1, y, z));
         neigh[1] = neigh[5] = FIX_ROT(get_data(state, DATA, x, y, z-1));
         neigh[2] = neigh[6] = FIX_ROT(get_data(state, DATA, x-1, y, z));
@@ -698,29 +670,7 @@ chunk_render(PyObject *self, PyObject *args) {
                      * grass, water, glass, chest, restone wire,
                      * ice, fence, portal, iron bars, glass panes,
                      * trapped chests, stairs */
-                    if ((state.block == block_grass) ||
-                        (state.block == block_flowing_water) || (state.block == block_water) ||
-                        (state.block == block_glass) || (state.block == block_chest) ||
-                        (state.block == block_redstone_wire) ||
-                        /* doors */
-                        (state.block == block_wooden_door  ) ||
-                        (state.block == block_iron_door    ) ||
-                        (state.block == block_spruce_door  ) ||
-                        (state.block == block_birch_door   ) ||
-                        (state.block == block_jungle_door  ) ||
-                        (state.block == block_acacia_door  ) ||
-                        (state.block == block_dark_oak_door) ||
-                        /* end doors */
-                        (state.block == block_ice) ||
-                        (state.block == block_fence) || (state.block == block_portal) ||
-                        (state.block == block_iron_bars) || (state.block == block_glass_pane) ||
-                        (state.block == block_waterlily) || (state.block == block_nether_brick_fence) ||
-                        (state.block == block_cobblestone_wall) || (state.block == block_double_plant) || 
-                        (state.block == block_stained_glass_pane) || (state.block == block_stained_glass) ||
-                        (state.block == block_trapped_chest) || (state.block == block_spruce_fence) ||
-                        (state.block == block_birch_fence) || (state.block == block_jungle_fence) ||
-                        (state.block == block_dark_oak_fence) || (state.block == block_acacia_fence) ||
-                        is_stairs(state.block)) {
+                    if (block_class_is_subset(state.block,block_class_ancil,block_class_ancil_len)) {
                         ancilData = generate_pseudo_data(&state, ancilData);
                         state.block_pdata = ancilData;
                     } else {
diff --git a/overviewer_core/src/utils.h b/overviewer_core/src/utils.h
index 02108b5..4003e96 100644
--- a/overviewer_core/src/utils.h
+++ b/overviewer_core/src/utils.h
@@ -14,4 +14,7 @@
 #define OV_BLEND(mask, in1, in2, tmp1, tmp2)\
         (OV_MULDIV255(in1, 255 - mask, tmp1) + OV_MULDIV255(in2, mask, tmp2))
 
-#endif
+#define count_of(array) \
+    (sizeof(array) / sizeof(array[0]))
+
+#endif
\ No newline at end of file
diff --git a/setup.py b/setup.py
index 4163147..b38c65a 100755
--- a/setup.py
+++ b/setup.py
@@ -175,7 +175,7 @@ for name in glob.glob("overviewer_core/src/primitives/*.c"):
     name = os.path.splitext(name)[0]
     primitives.append(name)
 
-c_overviewer_files = ['main.c', 'composite.c', 'iterate.c', 'endian.c', 'rendermodes.c']
+c_overviewer_files = ['main.c', 'composite.c', 'iterate.c', 'endian.c', 'rendermodes.c', 'block_class.c']
 c_overviewer_files += map(lambda mode: 'primitives/%s.c' % (mode,), primitives)
 c_overviewer_files += ['Draw.c']
 c_overviewer_includes = ['overviewer.h', 'rendermodes.h']