From 789690fc23a49aa3bcbc946992fd6340c90d8c10 Mon Sep 17 00:00:00 2001
From: "ich@christoph-bauer.net" <unknown>
Date: Sat, 27 Feb 2010 21:16:59 +0000
Subject: [PATCH] a faster appendFS

---
 compiler/utils/FastString.lhs |   13 ++++++++++++-
 1 file changed, 12 insertions(+), 1 deletion(-)

diff --git a/compiler/utils/FastString.lhs b/compiler/utils/FastString.lhs
index 29c7788..055f921 100644
--- a/compiler/utils/FastString.lhs
+++ b/compiler/utils/FastString.lhs
@@ -449,7 +449,18 @@ zEncodeFS fs@(FastString _ _ _ _ enc) =
             return efs
 
 appendFS :: FastString -> FastString -> FastString
-appendFS fs1 fs2 = mkFastString (unpackFS fs1 ++ unpackFS fs2)
+appendFS fs1 fs2 =
+  inlinePerformIO $ do
+    r <- mallocForeignPtrBytes len
+    withForeignPtr r $ \ r' -> do
+    withForeignPtr (buf fs1) $ \ fs1Ptr -> do
+    withForeignPtr (buf fs2) $ \ fs2Ptr -> do
+        copyBytes r' fs1Ptr len1
+        copyBytes (advancePtr r' len1) fs2Ptr len2
+        mkFastStringForeignPtr r' r len
+  where len  = len1 + len2
+        len1 = lengthFS fs1
+        len2 = lengthFS fs2
 
 concatFS :: [FastString] -> FastString
 concatFS ls = mkFastString (Prelude.concat (map unpackFS ls)) -- ToDo: do better
-- 
1.7.10.4