lib/Data/Time/Clock/POSIX.hs

    -- | POSIX time, if you need to deal with timestamps and the like.
    -- Most people won't need this module.
    module Data.Time.Clock.POSIX
    (
        posixDayLength,POSIXTime,posixSecondsToUTCTime,utcTimeToPOSIXSeconds,getPOSIXTime,getCurrentTime
    ) where

    import Data.Time.Clock.UTC
    import Data.Time.Calendar.Days
    import Data.Fixed
    import Control.Monad

    #include "HsTimeConfig.h"

    #ifdef mingw32_HOST_OS
    import Data.Word    ( Word64)
    import System.Win32.Time
    #elif HAVE_CLOCK_GETTIME
    import Data.Time.Clock.CTimespec
    import Foreign.C.Types (CTime(..))
    #else
    import Data.Time.Clock.CTimeval
    #endif

    -- | 86400 nominal seconds in every day
    posixDayLength :: NominalDiffTime
    posixDayLength = 86400

    -- | POSIX time is the nominal time since 1970-01-01 00:00 UTC
    --
    -- To convert from a 'Foreign.C.CTime' or 'System.Posix.EpochTime', use 'realToFrac'.
    --
    type POSIXTime = NominalDiffTime

    unixEpochDay :: Day
    unixEpochDay = ModifiedJulianDay 40587

    posixSecondsToUTCTime :: POSIXTime -> UTCTime
    posixSecondsToUTCTime i = let
        (d,t) = divMod' i posixDayLength
     in UTCTime (addDays d unixEpochDay) (realToFrac t)

    utcTimeToPOSIXSeconds :: UTCTime -> POSIXTime
    utcTimeToPOSIXSeconds (UTCTime d t) =
     (fromInteger (diffDays d unixEpochDay) * posixDayLength) + min posixDayLength (realToFrac t)

    -- | Get the current POSIX time from the system clock.
    getPOSIXTime :: IO POSIXTime

    #ifdef mingw32_HOST_OS
    -- On Windows, the equlvalent of POSIX time is "file time", defined as
    -- the number of 100-nanosecond intervals that have elapsed since
    -- 12:00 A.M. January 1, 1601 (UTC).  We can convert this into a POSIX
    -- time by adjusting the offset to be relative to the POSIX epoch.

    getPOSIXTime = do
      FILETIME ft <- System.Win32.Time.getSystemTimeAsFileTime
      return (fromIntegral (ft - win32_epoch_adjust) / 10000000)

    win32_epoch_adjust :: Word64
    win32_epoch_adjust = 116444736000000000

    #elif HAVE_CLOCK_GETTIME

    -- Use hi-res POSIX time
    ctimespecToPosixSeconds :: CTimespec -> POSIXTime
    ctimespecToPosixSeconds (MkCTimespec (CTime s) ns) =
        (fromIntegral s) + (fromIntegral ns) / 1000000000

    getPOSIXTime = liftM ctimespecToPosixSeconds getCTimespec

    #else

    -- Use POSIX time
    ctimevalToPosixSeconds :: CTimeval -> POSIXTime
    ctimevalToPosixSeconds (MkCTimeval s mus) = (fromIntegral s) + (fromIntegral mus) / 1000000

    getPOSIXTime = liftM ctimevalToPosixSeconds getCTimeval

    #endif

    -- | Get the current UTC time from the system clock.
    getCurrentTime :: IO UTCTime
    getCurrentTime = liftM posixSecondsToUTCTime getPOSIXTime