1 files changed, 40 insertions, 1 deletions

diff --git a/src/Network/Torrent/PeerWire/Block.hs b/src/Network/Torrent/PeerWire/Block.hs
index b2fe8c31..056f6b18 100644
--- a/src/Network/Torrent/PeerWire/Block.hs
+++ b/src/Network/Torrent/PeerWire/Block.hs
@@ -1,8 +1,14 @@
 module Network.Torrent.PeerWire.Block
        ( BlockIx(..), Block(..)
+       , defaultBlockSize
+       , blockRange, ixRange, pieceIx
+       , isPiece
        ) where
 
-import Data.ByteString (ByteString)
+import           Data.ByteString (ByteString)
+import qualified Data.ByteString as B
+import Data.Int
+
 
 data BlockIx = BlockIx {
     ixPiece  :: {-# UNPACK #-} !Int -- ^ Zero-based piece index.
@@ -15,3 +21,36 @@ data Block = Block {
   , blkOffset :: Int         -- ^ Zero-based byte offset within the piece.
   , blkData   :: ByteString  -- ^ Payload.
   } deriving (Show, Eq)
+
+
+-- | Widely used semi-official block size.
+defaultBlockSize :: Int
+defaultBlockSize = 16 * 1024
+
+
+isPiece :: Int -> Block -> Bool
+isPiece pieceSize (Block i offset bs) =
+  offset == 0 && B.length bs == pieceSize && i >= 0
+{-# INLINE isPiece #-}
+
+pieceIx :: Int -> Int -> BlockIx
+pieceIx i = BlockIx i 0
+{-# INLINE pieceIx #-}
+
+blockRange :: (Num a, Integral a) => Int -> Block -> (a, a)
+blockRange pieceSize blk = (offset, offset + len)
+  where
+    offset = fromIntegral pieceSize * fromIntegral (blkPiece blk)
+           + fromIntegral (blkOffset blk)
+    len    = fromIntegral (B.length (blkData blk))
+{-# INLINE blockRange #-}
+{-# SPECIALIZE blockRange :: Int -> Block -> (Int64, Int64) #-}
+
+ixRange :: (Num a, Integral a) => Int -> BlockIx -> (a, a)
+ixRange pieceSize ix = (offset, offset + len)
+  where
+    offset = fromIntegral  pieceSize * fromIntegral (ixPiece ix)
+           + fromIntegral (ixOffset ix)
+    len    = fromIntegral (ixLength ix)
+{-# INLINE ixRange #-}
+{-# SPECIALIZE ixRange :: Int -> BlockIx -> (Int64, Int64) #-}