Use expm1 defined locally only on windows

Numeric/SpecFunctions.hs

@@ -51,10 +51,11 @@ module Numeric.SpecFunctions (
   ) where
 
 import Numeric.SpecFunctions.Internal
-#if MIN_VERSION_base(4,9,0)
+#if MIN_VERSION_base(44,9,0)
 import GHC.Float (log1p, expm1)
 #endif
 
+
 -- $references
 --
 -- * Bernardo, J. (1976) Algorithm AS 103: Psi (digamma)

Numeric/SpecFunctions/Internal.hs

@@ -11,7 +11,7 @@
 -- Internal module with implementation of special functions.
 module Numeric.SpecFunctions.Internal where
 
-#if !MIN_VERSION_base(4,9,0)
+#if !MIN_VERSION_base(44,9,0)
 import Control.Applicative
 #endif
 import Data.Bits       ((.&.), (.|.), shiftR)
@@ -20,7 +20,7 @@ import Data.Word       (Word)
 import qualified Data.Vector.Unboxed as U
 import           Data.Vector.Unboxed   ((!))
 import Text.Printf
-#if MIN_VERSION_base(4,9,0)
+#if MIN_VERSION_base(44,9,0)
 import GHC.Float (log1p,expm1)
 #endif
 
@@ -722,7 +722,7 @@ sinc x
 ----------------------------------------------------------------
 
 -- GHC.Float provides log1p and expm1 since 4.9.0
-#if !MIN_VERSION_base(4,9,0)
+#if !MIN_VERSION_base(44,9,0)
 -- | Compute the natural logarithm of 1 + @x@.  This is accurate even
 -- for values of @x@ near zero, where use of @log(1+x)@ would lose
 -- precision.
@@ -764,16 +764,19 @@ log1p x
              ]
 -- | Compute @exp x - 1@ without loss of accuracy for x near zero.
 expm1 :: Double -> Double
+#ifdef USE_SYSTEM_GHC
+expm1 = c_expm1
+
+foreign import ccall "expm1" c_expm1 :: Double -> Double
+#else
 -- NOTE: this is simplest implementation and not terribly efficient.
 expm1 x
   | x < (-37.42994775023705) = -1
   | x > m_max_log            = m_pos_inf
   | abs x > 0.5              = exp x - 1
   | otherwise                = sumSeries $ liftA2 (*) (scanSequence (*) x (pure x))
                                                       (1 / scanSequence (*) 1 (enumSequenceFrom 2))
-
--- foreign import ccall "expm1" c_expm1 :: Double -> Double
--- MIN_VERSION_base(4,9,0)
+#endif
 #endif
 
 -- | Compute log(1+x)-x:

math-functions.cabal

@@ -39,11 +39,13 @@ library
     DeriveGeneric
 
   ghc-options:          -Wall -O2
-  build-depends:        base >=4.5 && <5,
-                        deepseq,
-                        vector >= 0.7,
-                        primitive,
-                        vector-th-unbox
+  build-depends:        base >=4.5 && <5
+                      , deepseq
+                      , vector >= 0.7
+                      , primitive
+                      , vector-th-unbox
+  if flag(system-expm1) || !os(windows)
+    cpp-options: -DUSE_SYSTEM_EXPM1
   exposed-modules:
     Numeric.MathFunctions.Constants
     Numeric.MathFunctions.Comparison
@@ -57,6 +59,11 @@ library
   other-modules:
     Numeric.SpecFunctions.Internal
 
+flag system-expm1
+     description: Use expm1 provided by system. Only have effect on windows
+     default:     False
+     manual:      True
+
 test-suite tests
   default-language: Haskell2010
   other-extensions: ViewPatterns