diff --git a/swarm/manager.py b/swarm/manager.py
index fd3adad..9828048 100644
--- a/swarm/manager.py
+++ b/swarm/manager.py
@@ -243,10 +243,10 @@ class Manager:
         self.bits_toggled_off = len(bits_off)
 
         for ndx in bits_on:
-            byte, bit = divmod(ndx, 8)
+            byte, bit = ndx >> 3, ndx & 7
             self.shmem.buf[OFFSET_STATE + byte] |= 0x80 >> bit
         for ndx in bits_off:
-            byte, bit = divmod(ndx, 8)
+            byte, bit = ndx >> 3, ndx & 7
             self.shmem.buf[OFFSET_STATE + byte] &= 0xFF ^ (0x80 >> bit)
 
         since_last_printout = time.time() - self.last_printout
@@ -268,7 +268,7 @@ class Manager:
         with Image.new("RGB", (1000, 1000), 0) as im:
             for i in range(1000000):
                 y, x = divmod(i, 1000)
-                byte, bit = divmod(i, 8)
+                byte, bit = i >> 3, i & 7
                 im.putpixel(
                     (x, y),
                     (
@@ -285,7 +285,7 @@ class Manager:
         with Image.new("L", (1000, 1000), 0) as im:
             for i in range(1000000):
                 y, x = divmod(i, 1000)
-                byte, bit = divmod(i, 8)
+                byte, bit = i >> 3, i & 7
                 im.putpixel(
                     (x, y),
                     255 if (buf[OFFSET_AVOID + byte] << bit) & 0x80 else 0,
@@ -313,7 +313,7 @@ class Manager:
     def add_avoid_range(self, rng: range):
         assert self.shmem is not None
         for ndx in rng:
-            byte, bit = divmod(ndx, 8)
+            byte, bit = ndx >> 3, ndx & 7
             self.shmem.buf[OFFSET_AVOID + byte] |= 0x80 >> bit
 
     def add_avoid_rect(self, sx: int, sy: int, w: int, h: int):
@@ -324,7 +324,7 @@ class Manager:
     def add_avoid_index(self, index: int):
         assert self.shmem is not None
         assert 0 <= index < 1000000
-        byte, bit = divmod(index, 8)
+        byte, bit = index >> 3, index & 7
         self.shmem.buf[OFFSET_AVOID + byte] |= 0x80 >> bit
 
     def add_avoid_image(self, im: Image.Image):
@@ -342,7 +342,7 @@ class Manager:
     def set_index(self, index: int, value: bool):
         assert 0 <= index <= 1000000
         assert self.shmem is not None
-        byte, bit = divmod(index, 8)
+        byte, bit = index >> 3, index & 7
         self.shmem.buf[OFFSET_MASK + byte] |= 0x80 >> bit
         if value:
             self.shmem.buf[OFFSET_CANVAS + byte] |= 0x80 >> bit
@@ -352,7 +352,7 @@ class Manager:
     def clear_index(self, index: int):
         assert 0 <= index <= 1000000
         assert self.shmem is not None
-        byte, bit = divmod(index, 8)
+        byte, bit = index >> 3, index & 7
         self.shmem.buf[OFFSET_MASK + byte] &= 0xFF ^ (0x80 >> bit)
         self.shmem.buf[OFFSET_CANVAS + byte] &= 0xFF ^ (0x80 >> bit)