From a467181b6aa21b1e41d56e7772d481cbf0c37f39 Mon Sep 17 00:00:00 2001
From: Sam Truzjan <pxqr.sta@gmail.com>
Date: Mon, 6 Jan 2014 00:01:49 +0400
Subject: Add check command to mktorrent utility

---
 src/Data/Torrent/Bitfield.hs | 13 +++++++++++++
 1 file changed, 13 insertions(+)

(limited to 'src/Data/Torrent/Bitfield.hs')

diff --git a/src/Data/Torrent/Bitfield.hs b/src/Data/Torrent/Bitfield.hs
index 8cdae69f..b65f058b 100644
--- a/src/Data/Torrent/Bitfield.hs
+++ b/src/Data/Torrent/Bitfield.hs
@@ -57,6 +57,7 @@ module Data.Torrent.Bitfield
        , isSubsetOf
 
          -- ** Availability
+       , complement
        , Frequency
        , frequencies
        , rarest
@@ -194,8 +195,20 @@ findMax :: Bitfield -> PieceIx
 findMax = S.findMax . bfSet
 {-# INLINE findMax #-}
 
+-- | Check if all pieces from first bitfield present if the second bitfield
 isSubsetOf :: Bitfield -> Bitfield -> Bool
 isSubsetOf a b = bfSet a `S.isSubsetOf` bfSet b
+{-# INLINE isSubsetOf #-}
+
+-- | Resulting bitfield includes only missing pieces.
+complement :: Bitfield -> Bitfield
+complement Bitfield {..} = Bitfield
+  { bfSet  = uni `S.difference` bfSet
+  , bfSize = bfSize
+  }
+  where
+    Bitfield _ uni = haveAll bfSize
+{-# INLINE complement #-}
 
 {-----------------------------------------------------------------------
 -- Availability
-- 
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