[vector] #31: Bug in unsafeToForeignPtr/unsafeFromForeignPtr

[vector]

#31: Bug in unsafeToForeignPtr/unsafeFromForeignPtr
-------------------------------+--------------------------------------------
Reporter:  patperry at gmail.com  |       Owner:     
    Type:  defect              |      Status:  new
Priority:  critical            |   Milestone:     
 Version:  0.6                 |    Keywords:     
-------------------------------+--------------------------------------------
 "unsafeToForeignPtr" and "unsafeFromForeignPtr" disagree on the definition
 of the offset.  This leads to bugs when these functions are used in
 combination with "slice".

 Using vector-0.6.0.2 in ghci 6.12.3 on Mac OS 10.6:

 {{{
 GHCi, version 6.12.3: http://www.haskell.org/ghc/  :? for help
 Loading package ghc-prim ... linking ... done.
 Loading package integer-gmp ... linking ... done.
 Loading package base ... linking ... done.
 Loading package ffi-1.0 ... linking ... done.
 Prelude> :m + Data.Vector.Storable
 Prelude Data.Vector.Storable> let x = fromList [ 0..3 ]
 Loading package primitive-0.3 ... linking ... done.
 Loading package array-0.3.0.1 ... linking ... done.
 Loading package containers-0.3.0.0 ... linking ... done.
 Loading package filepath-1.1.0.4 ... linking ... done.
 Loading package old-locale-1.0.0.2 ... linking ... done.
 Loading package old-time-1.0.0.5 ... linking ... done.
 Loading package unix-2.4.0.2 ... linking ... done.
 Loading package directory-1.0.1.1 ... linking ... done.
 Loading package pretty-1.0.1.1 ... linking ... done.
 Loading package process-1.0.1.3 ... linking ... done.
 Loading package Cabal-1.8.0.6 ... linking ... done.
 Loading package bytestring-0.9.1.7 ... linking ... done.
 Loading package ghc-binary-0.5.0.2 ... linking ... done.
 Loading package bin-package-db-0.0.0.0 ... linking ... done.
 Loading package hpc-0.5.0.5 ... linking ... done.
 Loading package template-haskell ... linking ... done.
 Loading package ghc-6.12.3 ... linking ... done.
 Loading package vector-0.6.0.2 ... linking ... done.
 Prelude Data.Vector.Storable> let y = slice 1 3 x
 Prelude Data.Vector.Storable> let (f,o,n) = unsafeToForeignPtr y
 Prelude Data.Vector.Storable> let y' = unsafeFromForeignPtr f o n
 Prelude Data.Vector.Storable> y
 fromList [1.0,2.0,3.0] :: Data.Vector.Storable.Vector
 Prelude Data.Vector.Storable> y'
 fromList [1.6984055785e-313,0.0,1.0] :: Data.Vector.Storable.Vector
 Prelude Data.Vector.Storable> unsafeToForeignPtr y
 (0x03188580,-1,3)
 Prelude Data.Vector.Storable> unsafeToForeignPtr y'
 (0x03188580,1,3)
 }}}

 The *real* source of the bug is that offsetToPtr and ptrToOffset disagree.
 The fix is easy: change the definition of ptrToOffset in
 Data.Vector.Storable.Internal from

 {{{
 ptrToOffset :: Storable a => ForeignPtr a -> Ptr a -> Int
 {-# INLINE ptrToOffset #-}
 ptrToOffset fp q = unsafeInlineIO
                  $ withForeignPtr fp $ \p -> return (distance p q)
 }}}

 to

 {{{
 ptrToOffset :: Storable a => ForeignPtr a -> Ptr a -> Int
 {-# INLINE ptrToOffset #-}
 ptrToOffset fp q = unsafeInlineIO
                  $ withForeignPtr fp $ \p -> return (distance q p)
 }}}

-- 
Ticket URL: <http://trac.haskell.org/vector/ticket/31>
vector <http://trac.haskell.org/vector>
Package vector