add units to disk size check message

Content.hs

@@ -39,6 +39,7 @@ import qualified Annex
 import Utility
 import StatFS
 import Key
+import DataUnits
 
 {- Checks if a given key is currently present in the gitAnnexLocation. -}
 inAnnex :: Key -> Annex Bool
@@ -129,11 +130,10 @@ checkDiskSpace' adjustment key = do
 		(Just (FileSystemStats { fsStatBytesAvailable = have }), Just need) ->
 			if (need + reserve > have + adjustment)
 				then error $ "not enough free space (have " ++ 
-					showsize (have + adjustment) ++ "; need " ++
+					roughSize True (have + adjustment) ++ "; need " ++
-					showsize (need + reserve) ++ ")"
+					roughSize True (need + reserve) ++ ")"
 				else return ()
 	where
-		showsize i = show i
 		megabyte :: Integer
 		megabyte = 1024 * 1024
 

DataUnits.hs

@@ -0,0 +1,66 @@
+{- data size display
+ -
+ - Copyright 2011 Joey Hess <joey@kitenet.net>
+ -
+ - Licensed under the GNU GPL version 3 or higher.
+ -}
+
+module DataUnits (roughSize) where
+
+{- And now a rant: 
+ -
+ - In the beginning, we had powers of two, and they were good.
+ -
+ - Disk drive manufacturers noticed that some powers of two were
+ - sorta close to some powers of ten, and that rounding down to the nearest
+ - power of ten allowed them to advertise their drives were bigger. This
+ - was sorta annoying.
+ -
+ - Then drives got big. Really, really big. This was good.
+ -
+ - Except that the small rounding error perpretrated by the drive
+ - manufacturers suffered the fate of a small error, and became a large
+ - error. This was bad.
+ -
+ - So, a committee was formed. And it arrived at a committee-like decision,
+ - which satisfied noone, confused everyone, and made the world an uglier
+ - place. As with all committees, this was meh.
+ -
+ - And the drive manufacturers happily continued selling drives that are
+ - increasingly smaller than you'd expect, if you don't count on your
+ - fingers. But that are increasingly bigger.
+ -
+ - Thus, I use units here that I loathe. Because if I didn't, people would
+ - be confused that their drives seem the wrong size, and other people would
+ - complain at me for not being standards compliant. And we call this
+ - progress?
+ -}
+
+{- approximate display of a particular number of bytes -}
+roughSize :: Bool -> Integer -> String
+roughSize short i
+	| i < 0 = "-" ++ roughSize short (negate i)
+	| i >= at 8 = units 8 "yottabyte" "YB"
+	| i >= at 7 = units 7 "zettabyte" "ZB"
+	| i >= at 6 = units 6 "exabyte" "EB"
+	| i >= at 5 = units 5 "petabyte" "PB"
+	| i >= at 4 = units 4 "terabyte" "TB"
+	| i >= at 3 = units 3 "gigabyte" "GB"
+	| i >= at 2 = units 2 "megabyte" "MB"
+	| i >= at 1 = units 1 "kilobyte" "kB"
+	| otherwise = units 0 "byte" "B"
+	where
+		at :: Integer -> Integer
+		at n = 1000^n
+
+		chop :: Integer -> Integer
+		chop d = round ((fromInteger i :: Double) / fromInteger (at d))
+
+		units :: Integer -> String -> String -> String
+		units d u u' = let num = chop d in
+			show num ++ " " ++
+			(if short then u' else plural num u)
+
+		plural n u
+			| n == 1 = u
+			| otherwise = u ++ "s"