1 files changed, 56 insertions, 0 deletions

diff --git a/src/Network/BitTorrent/PeerWire/Block.hs b/src/Network/BitTorrent/PeerWire/Block.hs
new file mode 100644
index 00000000..33e3dead
--- /dev/null
+++ b/src/Network/BitTorrent/PeerWire/Block.hs
@@ -0,0 +1,56 @@
+module Network.BitTorrent.PeerWire.Block
+       ( BlockIx(..), Block(..)
+       , defaultBlockSize
+       , blockRange, ixRange, pieceIx
+       , isPiece
+       ) where
+
+import           Data.ByteString (ByteString)
+import qualified Data.ByteString as B
+import Data.Int
+
+
+data BlockIx = BlockIx {
+    ixPiece  :: {-# UNPACK #-} !Int -- ^ Zero-based piece index.
+  , ixOffset :: {-# UNPACK #-} !Int -- ^ Zero-based byte offset within the piece.
+  , ixLength :: {-# UNPACK #-} !Int -- ^ Block size starting from offset.
+  } deriving (Show, Eq)
+
+data Block = Block {
+    blkPiece  :: Int         -- ^ Zero-based piece index.
+  , 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) #-}