[Haskell-cafe] Fast Integer Input

I need a function which has fast conversion from Bytestring to Integer. I am currently using this: import qualified Data.ByteString.Lazy.Char8 as BS readInteger :: BS.ByteString -> Integer readInteger x = case BS.readInteger x of Just (i,_) -> i Are there faster implementations? This function takes 1.8 seconds to convert 2000 integers of length 10^13000. I need it to be smaller that 0.5 sec. Is it possible?