{-# LANGUAGE ForeignFunctionInterface #-}
{-----------------------------------------------------------------
 
  (c) 2008-2009 Markus Dittrich 
 
  This program is free software; you can redistribute it 
  and/or modify it under the terms of the GNU General Public 
  License Version 3 as published by the Free Software Foundation. 
 
  This program is distributed in the hope that it will be useful,
  but WITHOUT ANY WARRANTY; without even the implied warranty of
  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  GNU General Public License Version 3 for more details.
 
  You should have received a copy of the GNU General Public 
  License along with this program; if not, write to the Free 
  Software Foundation, Inc., 59 Temple Place - Suite 330, 
  Boston, MA 02111-1307, USA.

--------------------------------------------------------------------}

-- | definition of a few additional helper function (e.g. from libc)
module ExtraFunctions ( real_exp 
                      , is_equal
                      ) where


-- imports
import Foreign()
import Foreign.C.Types
import Prelude 


-- | use glibc DBL_EPSILON
dbl_epsilon :: Double
dbl_epsilon = 2.2204460492503131e-16

-- | comparison function for doubles via dbl_epsion
is_equal :: Double -> Double -> Bool
is_equal x y = abs(x-y) <= abs(x) * dbl_epsilon


-- | helper function for defining real powers
-- NOTE: We use glibc's pow function since it is more
-- precise than implementing it ourselves via, e.g.,
-- pow a x = exp $ x * log a
foreign import ccall "math.h pow"
        c_pow :: CDouble -> CDouble -> CDouble

real_exp :: Double -> Double -> Double
real_exp a x = realToFrac $ c_pow (realToFrac a) (realToFrac x)