--- a/util/hex.lua	Sat Dec 20 21:34:59 2014 +0100
+++ b/util/hex.lua	Mon Jan 12 15:10:37 2015 +0100
@@ -1,19 +1,25 @@
 local s_char = string.char;
+local s_format = string.format;
+local s_gsub = string.gsub;
+
+local char_to_hex = {};
+local hex_to_char = {};
 
-local function char_to_hex(c)
-	return ("%02x"):format(c:byte())
-end
-
-local function hex_to_char(h)
-	return s_char(tonumber(h, 16));
+do
+	local char, hex;
+	for i = 0,255 do
+		char, hex = s_char(i), s_format("%02x", i);
+		char_to_hex[char] = hex;
+		hex_to_char[hex] = char;
+	end
 end
 
 local function to(s)
-	return s:gsub(".", char_to_hex);
+	return (s_gsub(s, ".", char_to_hex));
 end
 
 local function from(s)
-	return s:gsub("..", hex_to_char);
+	return (s_gsub(s, "..", hex_to_char));
 end
 
 return { to = to, from = from }