diff --git a/Biobase/Types/Partition.hs b/Biobase/Types/Partition.hs
--- a/Biobase/Types/Partition.hs
+++ b/Biobase/Types/Partition.hs
@@ -1,4 +1,5 @@
 
+{-# LANGUAGE ForeignFunctionInterface #-}
 {-# LANGUAGE StandaloneDeriving #-}
 {-# LANGUAGE MultiParamTypeClasses #-}
 {-# LANGUAGE GeneralizedNewtypeDeriving #-}
@@ -17,23 +18,33 @@
 -- | Some default instances. Left out the Num one, so that you have to
 -- explicitly instanciate if you want to go around the Ring structure.
 
-newtype Partition = Partition {unPartition :: Double}
+newtype Partition = Partition {unPartition' :: Double}
   deriving (Show, Read, Eq, Ord)
 
+-- |
 
+mkPartition :: Double -> Partition
+mkPartition x
+  | x < 0     = error $ "mkPartition: prob <0: " ++ show x
+  | x > 1     = error $ "mkPartition: prob >1: " ++ show x
+  | otherwise = Partition $ log x
 
+unPartition :: Partition -> Double
+unPartition (Partition x) = exp x
+
+
 -- | Ring operations over Partition values.
 
 instance Ring Partition where
-  (Partition a) .+. (Partition b) = Partition $ a + b
+  (Partition a) .+. (Partition b) = Partition $ logSum a b
   {-# INLINE (.+.) #-}
-  (Partition a) .*. (Partition b) = Partition $ a * b
+  (Partition a) .*. (Partition b) = Partition $ a + b
   {-# INLINE (.*.) #-}
-  (Partition a) .^. k = Partition $ a ^ k
+  (Partition a) .^. k = Partition $ a * fromIntegral k
   {-# INLINE (.^.) #-}
   (Partition a) .^^. k = error ".^^. not defined for Partition" -- Partition $ a ^^ k
   {-# INLINE (.^^.) #-}
-  neg (Partition a) = Partition $ negate a
+  neg (Partition a) = error $ "negate partition? " ++ show a -- Partition $ negate a
   {-# INLINE neg #-}
   one = Partition 1
   {-# INLINE one #-}
@@ -42,11 +53,32 @@
   isZero (Partition a) = a == 0 -- TODO use some epsilon?
   {-# INLINE isZero #-}
 
+logSum :: Double -> Double -> Double
+logSum a b
+  | a>b       = f a b
+  | otherwise = f b a
+  where
+    f x y = x + log1p (exp $ y - x)
+    {-# INLINE f #-}
+{-# INLINE logSum #-}
 
 
--- * Vector instances.
 
+-- * Vector (and Prim) instances.
+
 deriving instance VGM.MVector VU.MVector Partition
 deriving instance VG.Vector VU.Vector Partition
 deriving instance VU.Unbox Partition
 deriving instance Prim Partition
+
+
+
+-- * math.h function for log/exp on pm1 are /much/ more efficient (what is
+-- haskell doing?)
+
+foreign import ccall unsafe "math.h log1p"
+    log1p :: Double -> Double
+
+foreign import ccall unsafe "math.h expm1"
+    expm1 :: Double -> Double
+
diff --git a/BiobaseTypes.cabal b/BiobaseTypes.cabal
--- a/BiobaseTypes.cabal
+++ b/BiobaseTypes.cabal
@@ -1,10 +1,10 @@
 name:           BiobaseTypes
-version:        0.0.2.1
+version:        0.0.2.2
 author:         Christian Hoener zu Siederdissen
 maintainer:     choener@tbi.univie.ac.at
 copyright:      Christian Hoener zu Siederdissen, 2010
 category:       Bioinformatics
-synopsis:       Ring class, with several instances.
+synopsis:       (deprecated) Ring class, with several instances.
 license:        GPL-3
 license-file:   LICENSE
 build-type:     Simple