Apply different scaling computation

src/System/Random.hs

@@ -357,7 +357,7 @@ class Random a where
   -- independently:
   --
   -- >>> fst $ randomR (('a', 5.0), ('z', 10.0)) $ mkStdGen 26
-  -- ('z',7.27305019146949)
+  -- ('z',7.72694980853051)
   --
   -- In case when a lawful range is desired `uniformR` should be used
   -- instead.

src/System/Random/Internal.hs

@@ -1394,13 +1394,16 @@ instance UniformRange Double where
     | l == h = return l
     | isInfinite l || isInfinite h =
       -- Optimisation exploiting absorption:
-      --   (-Infinity) + (anything but +Infinity) = -Infinity
-      --   (anything but -Infinity) + (+Infinity) = +Infinity
-      --                (-Infinity) + (+Infinity) = NaN
+      --    (+Infinity) + (-Infinity) = NaN
+      --    (-Infinity) + (+Infinity) = NaN
+      --    (+Infinity) + _           = +Infinity
+      --    (-Infinity) + _           = -Infinity
+      --              _ + (+Infinity) = +Infinity
+      --              _ + (-Infinity) = -Infinity
       return $! h + l
     | otherwise = do
       x <- uniformDouble01M g
-      return $! x * l + (1 - x) * h
+      pure $! scaleFloating l h x
   {-# INLINE uniformRM #-}
   isInRange = isInRangeOrd
 
@@ -1437,13 +1440,25 @@ instance UniformRange Float where
   uniformRM (l, h) g
     | l == h = return l
     | isInfinite l || isInfinite h =
+      -- Optimisation exploiting absorption:
+      -- Optimisation exploiting absorption:
+      --    (+Infinity) + (-Infinity) = NaN
+      --    (-Infinity) + (+Infinity) = NaN
+      --    (+Infinity) + _           = +Infinity
+      --    (-Infinity) + _           = -Infinity
+      --              _ + (+Infinity) = +Infinity
+      --              _ + (-Infinity) = -Infinity
       return $! h + l
     | otherwise = do
       x <- uniformFloat01M g
-      return $! x * l + (1 - x) * h
+      pure $! scaleFloating l h x
   {-# INLINE uniformRM #-}
   isInRange = isInRangeOrd
 
+scaleFloating :: (Ord a, Num a) => a -> a -> a -> a
+scaleFloating l h x = if abs l < abs h then l + x * (h - l) else h + x * (l - h)
+{-# INLINE scaleFloating #-}
+
 -- | Generates uniformly distributed 'Float' in the range \([0, 1]\).
 --   Numbers are generated by generating uniform 'Word32' and dividing
 --   it by \(2^{32}\). It's used to implement 'UniformRange' instance for 'Float'.