Jaime Blasco Blog

local bit = require("bit")
local band, bor, bxor = bit.band, bit.bor, bit.bxor

function checksum(card)
	num = 0
	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 % 10) == 0)
	
end