winio: Don't drop buffer offset in byteView/cwcharView

2 files changed, 5 insertions, 6 deletions

diff --git a/libraries/base/GHC/IO/Buffer.hs b/libraries/base/GHC/IO/Buffer.hs
index 85d7e7c310..167bc2a346 100644
--- a/libraries/base/GHC/IO/Buffer.hs
+++ b/libraries/base/GHC/IO/Buffer.hs
@@ -64,10 +64,6 @@ module GHC.IO.Buffer (
     charSize,
  ) where
 
-#if defined(CHARBUF_UTF16)
-import Data.Word (Word64)
-#endif
-
 import GHC.Base
 -- import GHC.IO
 import GHC.Num
@@ -268,6 +264,9 @@ bufferOffset Buffer{ bufOffset=off } = off
 bufferAdjustOffset :: Word64 -> Buffer e -> Buffer e
 bufferAdjustOffset offs buf = buf{ bufOffset=offs }
 
+-- The adjustment to the offset can be 32bit int on 32 platforms.
+-- This is fine, we only use this after reading into/writing from
+-- the buffer so we will never overflow here.
 bufferAddOffset :: Int -> Buffer e -> Buffer e
 bufferAddOffset offs buf@Buffer{ bufOffset=w } =
   buf{ bufOffset=w+(fromIntegral offs) }
diff --git a/libraries/base/GHC/IO/Encoding/CodePage/API.hs b/libraries/base/GHC/IO/Encoding/CodePage/API.hs
index 48afa90f69..41bc8d0f07 100644
--- a/libraries/base/GHC/IO/Encoding/CodePage/API.hs
+++ b/libraries/base/GHC/IO/Encoding/CodePage/API.hs
@@ -180,10 +180,10 @@ saner code ibuf obuf = do
    else return (why,            bufL ibuf' - bufL ibuf, ibuf', obuf')
 
 byteView :: Buffer CWchar -> Buffer Word8
-byteView (Buffer {..}) = Buffer { bufState = bufState, bufRaw = castForeignPtr bufRaw, bufSize = bufSize * 2, bufOffset = 0, bufL = bufL * 2, bufR = bufR * 2 }
+byteView (Buffer {..}) = Buffer { bufState = bufState, bufRaw = castForeignPtr bufRaw, bufSize = bufSize * 2, bufOffset = bufOffset, bufL = bufL * 2, bufR = bufR * 2 }
 
 cwcharView :: Buffer Word8 -> Buffer CWchar
-cwcharView (Buffer {..}) = Buffer { bufState = bufState, bufRaw = castForeignPtr bufRaw, bufSize = half bufSize, bufOffset = 0, bufL = half bufL, bufR = half bufR }
+cwcharView (Buffer {..}) = Buffer { bufState = bufState, bufRaw = castForeignPtr bufRaw, bufSize = half bufSize, bufOffset = bufOffset, bufL = half bufL, bufR = half bufR }
   where half x = case x `divMod` 2 of (y, 0) -> y
                                       _      -> errorWithoutStackTrace "cwcharView: utf16_(encode|decode) (wrote out|consumed) non multiple-of-2 number of bytes"