faster file loading.

1 files changed, 29 insertions, 0 deletions

diff --git a/ByteStringUtil.hs b/ByteStringUtil.hs
new file mode 100644
index 0000000..9711e0b
--- /dev/null
+++ b/ByteStringUtil.hs
@@ -0,0 +1,29 @@
+module ByteStringUtil where
+
+import Data.ByteString.Lazy.Internal
+import Data.ByteString.Lazy as L
+import qualified Data.ByteString as S
+import System.IO
+import System.IO.Unsafe
+
+oneMeg :: Int
+oneMeg = 1048576
+
+hGetContentsN :: Int -> Handle -> IO ByteString
+hGetContentsN kk h = lazyRead
+  where
+    k = kk - chunkOverhead
+    lazyRead = unsafeInterleaveIO loop
+
+    loop = do
+        c <- S.hGetSome h k -- only blocks if there is no data available
+        if S.null c
+          then hClose h >> return Empty
+          else do cs <- lazyRead
+                  return (Chunk c cs)
+
+readBigFile :: FilePath -> IO ByteString
+readBigFile fname = do
+    h <- openFile fname ReadMode
+    hGetContentsN oneMeg h
+