diff --git a/Git/PackIndex.hs b/Git/PackIndex.hs
new file mode 100644
index 0000000..49055ee
--- /dev/null
+++ b/Git/PackIndex.hs
@@ -0,0 +1,127 @@
+{-# LANGUAGE RecordWildCards #-}
+{-# OPTIONS -Wall #-}
+
+module Git.PackIndex (
+        dumpRawPackIndex,
+
+        -- * Paths
+        idxPath
+) where
+
+import Control.Applicative ((<$>))
+import Control.Monad (forM_)
+import qualified Data.ByteString as BS
+import Data.Word (Word32)
+import Foreign.Ptr
+import Foreign.Storable
+import Data.Storable.Endian
+import System.FilePath
+import System.IO.MMap
+import System.Posix.Types
+import Text.Printf
+
+import Git.Path
+
+------------------------------------------------------------
+
+data IDX = IDX1 {
+      idx1Size       :: Int
+    , idx1Fanout     :: Ptr (BigEndian Word32)
+    , idx1Offsets    :: Ptr (BigEndian Word32)
+    } | IDX2 {
+      idx2Size       :: Int
+    , idx2Fanout     :: Ptr (BigEndian Word32)
+    , idx2SHA1s      :: Ptr (BigEndian Word32)
+    , idx2CRCs       :: Ptr (BigEndian Word32)
+    , idx2Offsets    :: Ptr (BigEndian Word32)
+    , idx264bOffsets :: Ptr (BigEndian Word32)
+    -- , idx2PackCSum   :: Ptr (BigEndian Word32)
+    -- , idx2IdxCSum    :: Ptr (BigEndian Word32)
+    }
+
+------------------------------------------------------------
+-- | Public API
+
+-- | Number of objects in the corresponding .pack file
+idxSize   :: IDX -> Int
+idxSize IDX1{..} = idx1Size
+idxSize IDX2{..} = idx2Size
+
+-- | Nth SHA1
+idxSha1   :: IDX -> Int -> IO (Maybe BS.ByteString)
+idxSha1 IDX1{..} n
+    | n >= idx1Size = return Nothing
+    | otherwise     = do
+        cs <- peekByteOff idx1Offsets (4 + (n * 24))
+        Just <$> BS.packCStringLen (cs, 20)
+idxSha1 IDX2{..} n
+    | n >= idx2Size = return Nothing
+    | otherwise     = do
+        cs <- peekByteOff idx2SHA1s (n * 20)
+        Just <$> BS.packCStringLen (cs, 20)
+
+-- | Nth CRC
+idxCRC    :: IDX -> Int -> IO (Maybe Word32)
+idxCRC IDX1{}   _ = return Nothing
+idxCRC IDX2{..} n
+    | n >= idx2Size = return Nothing
+    | otherwise     = do
+        BE crc <- peekElemOff idx2CRCs n
+        return (Just crc)
+
+-- | Nth offset
+idxOffset :: IDX -> Int -> IO (Maybe FileOffset)
+idxOffset IDX1{..} n
+    | n >= idx1Size = return Nothing
+    | otherwise     = do
+        BE off <- peekByteOff idx1Offsets (n * 24)
+        return . Just . fromIntegral $ (off :: Word32)
+idxOffset IDX2{..} n
+    | n >= idx2Size = return Nothing
+    | otherwise     = do
+        BE off <- peekElemOff idx2Offsets n
+        return . Just . fromIntegral $ off
+
+------------------------------------------------------------
+
+-- | Generate the pathname for a given packfile
+idxPath :: String -> IO FilePath
+idxPath idx = gitPath ("objects" </> "pack" </> ("pack-" ++ idx ++ ".idx"))
+
+idxHeader :: Word32
+idxHeader = 0xff744f63
+
+dumpRawPackIndex :: FilePath -> IO String
+dumpRawPackIndex fp = do
+    (ptr, rawsize, offset, size) <- mmapFilePtr fp ReadOnly Nothing
+    let start :: Ptr (BigEndian Word32)
+        start = ptr `plusPtr` offset
+    BE hdr <- peek start
+    idx <- if (hdr == idxHeader)
+        then do
+            BE ver <- peekElemOff start 1
+            case ver of
+                2 -> mkIDX2 start size
+                _ -> error "Unknown version"
+        else mkIDX1 start size
+    return $ "Mapped region offset " ++ (show offset) ++ " size " ++ (show size) ++ " with " ++ show (idxSize idx) ++ " objects"
+
+mkIDX1 :: Ptr (BigEndian Word32) -> Int -> IO IDX
+mkIDX1 start size = do
+    let fanout = start
+    BE n <- peekElemOff fanout 255
+    let n' = fromIntegral (n :: Word32)
+    let offsets = fanout `plusPtr` (256 * 4)
+    return (IDX1 n' fanout offsets)
+
+mkIDX2 :: Ptr (BigEndian Word32) -> Int -> IO IDX
+mkIDX2 start size = do
+    let fanout = start `plusPtr` (2 * 4)
+    BE n <- peekElemOff fanout 255
+    let n' = fromIntegral (n :: Word32)
+    let sha1s = fanout `plusPtr` (256 * 4)
+        crcs = sha1s `plusPtr` (n' * 20)
+        offsets = crcs `plusPtr` (n' * 4)
+        offset64s = offsets `plusPtr` (n' * 4)
+    return (IDX2 n' fanout sha1s crcs offsets offset64s)
+    
diff --git a/ght.cabal b/ght.cabal
index 63ca49f..d7d81dc 100644
--- a/ght.cabal
+++ b/ght.cabal
@@ -22,10 +22,13 @@ library
                      old-locale,
                      time,
                      iteratee,
-                     iteratee-compress
+                     iteratee-compress,
+                     mmap,
+                     storable-endian
     Exposed-Modules: Git.Blob
                      Git.Commit
                      Git.Pack
+                     Git.PackIndex
                      Git.Path
 
 ------------------------------------------------------------
diff --git a/tools/ght.hs b/tools/ght.hs
index e266990..f8ae912 100644
--- a/tools/ght.hs
+++ b/tools/ght.hs
@@ -12,6 +12,7 @@ import UI.Command
 import Git.Blob
 import Git.Commit
 import Git.Pack
+import Git.PackIndex
 import Git.Path
 
 -- show-prefix, show-root use these
@@ -146,6 +147,29 @@ fPack (pack:_) = do
         then return pack
         else packPath pack
 
+------------------------------------------------------------
+-- show-idx
+--
+
+ghtShowIdx = defCmd {
+       	        cmdName = "show-idx",
+                cmdHandler = ghtShowIdxHandler,
+                cmdCategory = "Blob management",
+                cmdShortDesc = "Show the raw dump of a pack index",
+                cmdExamples = [("Show raw contents of pack pack-abcd.idx", "abcd")]
+        }
+
+ghtShowIdxHandler = do
+        idx <- (liftIO . fIdx =<< appArgs)
+        x <- liftIO $ dumpRawPackIndex idx
+	liftIO $ putStrLn x
+
+fIdx (idx:_) = do
+    exists <- doesFileExist idx
+    if exists
+        then return idx
+        else idxPath idx
+
 ------------------------------------------------------------
 -- show-raw
 --
@@ -218,7 +242,7 @@ ght = def {
 	        appCategories = ["Reporting", "Blob management"],
 		appSeeAlso = ["git"],
 		appProject = "Ght",
-	        appCmds = [ghtShowPrefix, ghtShowRoot, ghtShow, ghtLog, ghtShowRaw, ghtShowPack, ghtHashObject, ghtBranch]
+	        appCmds = [ghtShowPrefix, ghtShowRoot, ghtShow, ghtLog, ghtShowRaw, ghtShowPack, ghtShowIdx, ghtHashObject, ghtBranch]
 	}
 
 longDesc = "This is a bunch of trivial routines for inspecting git repositories. It is in no way useful beyond that."