Binary to Decimal

function Bin2Dec(s)
     local num = 0
     local ex = string.len(s) - 1
     local l = 0
     l = ex + 1
     for i = 1, l do
          b = string.sub(s, i, i)
          if b == "1" then
               num = num + 2^ex
          end
          ex = ex - 1
     end
     return string.format("%u", num)
end