added Lua script to generate an IMEI

We currently use a Python script to generate IMEIs. Loading Python is
relatively expensive on our target platform so I hope we can use
something quicker.

files/lib/blue-merle/luhn.lua

@@ -0,0 +1,61 @@
+---- Adapted from https://cybersecurity.att.com/blogs/labs-research/luhn-checksum-algorithm-lua-implementation
+
+local bit = require("bit")
+
+local band, bor, bxor = bit.band, bit.bor, bit.bxor
+
+function luhn_checksum(card)
+    local num = 0
+    local nDigits = card:len()
+	odd = band(nDigits, 1)
+
+	for count = 0,nDigits-1 do
+
+		digit = tonumber(string.sub(card, count+1,count+1))
+
+		if (bxor(band(count, 1),odd)) == 0
+		then
+		        digit = digit * 2
+        end
+
+        if digit > 9 then
+                digit = digit - 9
+        end
+
+        num = num + digit
+    end
+
+	return num
+end
+
+function luhn_digit (s)
+	local num = luhn_checksum (s)
+    return (10 - (num % 10))
+end
+
+function is_valid_luhn (s)
+	local num = luhn_checksum (s)
+    return ((num % 10) == 0)
+end
+
+
+function make_imei (premei)
+	local imei = premei .. tostring(luhn_digit(premei .. "0"))
+	if is_valid_luhn (imei) then print ("Valid " .. imei) end
+
+	return imei
+end
+
+function make_random_imei ()
+    local nDigits = 13
+    local premei = ""
+	for count = 0, nDigits-1 do
+	    premei = premei .. tostring (math.random (0, 9))
+	end
+
+	local imei = make_imei (tostring (premei))
+
+	return imei
+end
+
+print (make_imei ("354809108035177"))