Christopher Done wrote:
betterStdGen :: IO StdGen
Here's what I have been using. It's a bit more complete.
Of course, you can always use mkStdGen with
it to get one of those if you want. (Yes, I often
do that. StdGen is much maligned, but it's pretty good
at what it's designed for.)
Regards,
Yitz
module DevRandom where
import System.IO
import System.IO.Error
import Foreign.Marshal.Alloc
import Foreign.Storable
import Foreign.Ptr
data BlockingMode = Blocking | NonBlocking
deriving (Eq, Show)
-- Read data from the system random device.
-- Return Nothing if there is currently not
-- enough entropy in the system random device.
devRandom :: Storable a = IO (Maybe a)
devRandom = readDev /dev/random NonBlocking
-- Read data from the system random device.
-- If necessary, wait until there is
-- enough entropy in the system random device.
devRandomWait :: Storable a = IO a
devRandomWait = readDev dev Blocking = maybe (devRandomError dev) return
where
dev = /dev/random
-- Read data from the system random device.
-- If there is currently not enough entropy
-- in the system random device, use a lower
-- quality source of randomness instead.
devURandom :: Storable a = IO a
devURandom = readDev dev NonBlocking = maybe (devRandomError dev) return
where
dev = /dev/urandom
readDev :: Storable a = FilePath - BlockingMode - IO (Maybe a)
readDev dev mode = do
h - openFile dev ReadMode
hSetBuffering h NoBuffering
alloca $ getMaybe h undefined
where
getMaybe :: Storable a = Handle - a - Ptr a - IO (Maybe a)
getMaybe h undef ptr = do
let size = sizeOf undef
n - case mode of
Blocking- hGetBufh ptr size
NonBlocking - hGetBufNonBlocking h ptr size
if n size
then return Nothing
else fmap Just $ peek ptr
devRandomError :: FilePath - IO a
devRandomError p = ioError $ mkIOError illegalOperationErrorType
Unable to read from the system random device Nothing (Just p)
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