Init.hs

-- Module    : System.Random.TF.Init
-- Copyright : (c) 2013 Michał Pałka
-- License   : BSD3
--
-- Maintainer  : michal.palka@chalmers.se
-- Stability   : experimental
-- Portability : portable
--
module System.Random.TF.Init
 where

import Control.Monad (when)

--import Data.Int
import Data.Word

import Foreign

import Data.Ratio (numerator, denominator)
import Data.Time
import System.CPUTime
import System.IO

-- | Use system time create the random seed.
-- This method of seeding may not be relible.
mkSeedTime :: IO (Word64, Word64, Word64, Word64)
mkSeedTime = do
  utcTm <- getCurrentTime
  cpu <- getCPUTime
  let daytime = toRational $ utctDayTime utcTm
      t1, t2 :: Word64
      t1 = fromIntegral $ numerator daytime
      t2 = fromIntegral $ denominator daytime
      day = toModifiedJulianDay $ utctDay utcTm
      d1 :: Word64
      d1 = fromIntegral day
      c1 :: Word64
      c1 = fromIntegral cpu
  return (t1, t2, d1, c1)

-- | Use the UNIX special file @\/dev\/urandom@ to create the seed.
-- Inspired by @random-mwc@.
mkSeedUnix :: IO (Word64, Word64, Word64, Word64)
mkSeedUnix = do
  let bytes = 32
      rfile = "/dev/urandom"
  l <- allocaBytes bytes $ \buf -> do
    nread <- withBinaryFile rfile ReadMode $ \h ->
      hGetBuf h buf bytes
    when (nread /= bytes) $
      fail $ "mkSeedUnix: Failed to read " ++
        show bytes ++ " from " ++ rfile
    peekArray 4 buf
  let [x1, x2, x3, x4] = l
  return (x1, x2, x3, x4)