percentage library

Command/Status.hs

@@ -12,7 +12,6 @@ module Command.Status where
 import Control.Monad.State.Strict
 import qualified Data.Map as M
 import Text.JSON
-import Data.Ratio
 
 import Common.Annex
 import qualified Types.Backend as B
@@ -31,6 +30,7 @@ import Logs.UUID
 import Logs.Trust
 import Remote
 import Config
+import Utility.Percentage
 
 -- a named computation that produces a statistic
 type Stat = StatState (Maybe (String, StatState String))
@@ -161,7 +161,7 @@ bloom_info = stat "bloom filter size" $ json id $ do
 	let note = aside $
 		if localkeys >= capacity
 		then "appears too small for this repository; adjust annex.bloomcapacity"
-		else show (floor (percentage capacity localkeys) :: Integer) ++ "% full"
+		else showPercentage 1 (percentage capacity localkeys) ++ " full"
 
 	-- Two bloom filters are used at the same time, so double the size
 	-- of one.
@@ -170,10 +170,6 @@ bloom_info = stat "bloom filter size" $ json id $ do
 
 	return $ size ++ note
 
-	where
-		percentage :: Integer -> Integer -> Double
-		percentage full have = 100 * (fromRational $ have % full)
-
 disk_size :: Stat
 disk_size = stat "available local disk space" $ json id $ lift $
 	calcfree

Utility/Percentage.hs

@@ -0,0 +1,38 @@
+{- percentages
+ -
+ - Copyright 2012 Joey Hess <joey@kitenet.net>
+ -
+ - Licensed under the GNU GPL version 3 or higher.
+ -}
+
+module Utility.Percentage (
+	Percentage,
+	percentage,
+	showPercentage
+) where
+
+import Data.Ratio
+
+newtype Percentage = Percentage (Ratio Integer)
+
+instance Show Percentage where
+	show = showPercentage 0
+
+{- Normally the big number comes first. But 110% is allowed if desired. :) -}
+percentage :: Integer -> Integer -> Percentage
+percentage 0 _ = Percentage 0
+percentage full have = Percentage $ have * 100 % full
+
+{- Pretty-print a Percentage, with a specified level of precision. -}
+showPercentage :: Int -> Percentage -> String
+showPercentage precision (Percentage p)
+	| precision == 0 || remainder == 0 = go $ show int
+	| otherwise = go $ show int ++ "." ++ strip0s (show remainder)
+	where
+		go v = v ++ "%"
+		int :: Integer
+		(int, frac) = properFraction (fromRational p)
+		remainder = floor (frac * multiplier) :: Integer
+		strip0s = reverse . dropWhile (== '0') . reverse
+		multiplier :: Float
+		multiplier = 10 ** (fromIntegral precision)