diff --git a/util/init.lua b/util/init.lua
index 92c590a..64cd615 100644
--- a/util/init.lua
+++ b/util/init.lua
@@ -4,4 +4,18 @@ function Util.toHexChar(v)
   return ("0123456789ABCDEF"):sub(v, v)
 end
 
+function Util.fromHexChar(c)
+  local index = ({("0123456789ABCDEF"):find(c)})[1]
+  if index ~= nil then
+    return index - 1
+  end
+  return nil
+end
+
+function Util.boundCheck(x, y, w, h)
+  if x < 1 or x > w or y < 1 or y > h then
+    error(("Index out of range: (%d %d) is not within ([1,%d], [1,%d])"):format(x, y, w, h))
+  end
+end
+
 return Util
\ No newline at end of file