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{-# LANGUAGE Trustworthy #-}
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{-# LANGUAGE CPP, NondecreasingIndentation, ForeignFunctionInterface #-}

-----------------------------------------------------------------------------
-- |
-- Module      :  System.CPUTime
-- Copyright   :  (c) The University of Glasgow 2001
-- License     :  BSD-style (see the file libraries/base/LICENSE)
-- 
-- Maintainer  :  libraries@haskell.org
-- Stability   :  provisional
-- Portability :  portable
--
-- The standard CPUTime library.
--
-----------------------------------------------------------------------------

module System.CPUTime 
        (
         getCPUTime,       -- :: IO Integer
         cpuTimePrecision  -- :: Integer
        ) where

import Prelude

import Data.Ratio


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import Foreign.Safe
import Foreign.C

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-- For _SC_CLK_TCK

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-- For struct rusage

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-- For FILETIME etc. on Windows

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-- for CLK_TCK

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-- for struct tms

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-- -----------------------------------------------------------------------------
-- |Computation 'getCPUTime' returns the number of picoseconds CPU time
-- used by the current program.  The precision of this result is
-- implementation-dependent.

getCPUTime :: IO Integer
getCPUTime = do


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     -- NOTE: GetProcessTimes() is only supported on NT-based OSes.
     -- The counts reported by GetProcessTimes() are in 100-ns (10^-7) units.
    allocaBytes (8) $ \ p_creationTime -> do
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    allocaBytes (8) $ \ p_exitTime -> do
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    allocaBytes (8) $ \ p_kernelTime -> do
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    allocaBytes (8) $ \ p_userTime -> do
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    pid <- getCurrentProcess
    ok <- getProcessTimes pid p_creationTime p_exitTime p_kernelTime p_userTime
    if toBool ok then do
      ut <- ft2psecs p_userTime
      kt <- ft2psecs p_kernelTime
      return (ut + kt)
     else return 0
  where 
        ft2psecs :: Ptr FILETIME -> IO Integer
        ft2psecs ft = do
          high <- ((\hsc_ptr -> peekByteOff hsc_ptr 4)) ft :: IO Word32
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          low  <- ((\hsc_ptr -> peekByteOff hsc_ptr 0))  ft :: IO Word32
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            -- Convert 100-ns units to picosecs (10^-12) 
            -- => multiply by 10^5.
          return (((fromIntegral high) * (2^(32::Int)) + (fromIntegral low)) * 100000)

    -- ToDo: pin down elapsed times to just the OS thread(s) that
    -- are evaluating/managing Haskell code.

type FILETIME = ()
type HANDLE = ()
-- need proper Haskell names (initial lower-case character)
foreign import stdcall unsafe "GetCurrentProcess" getCurrentProcess :: IO (Ptr HANDLE)
foreign import stdcall unsafe "GetProcessTimes" getProcessTimes :: Ptr HANDLE -> Ptr FILETIME -> Ptr FILETIME -> Ptr FILETIME -> Ptr FILETIME -> IO CInt


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-- |The 'cpuTimePrecision' constant is the smallest measurable difference
-- in CPU time that the implementation can record, and is given as an
-- integral number of picoseconds.


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cpuTimePrecision :: Integer
cpuTimePrecision = round ((1000000000000::Integer) % fromIntegral (clockTicks))

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clockTicks :: Int
clockTicks =

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    (1000)
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