On Jun 19, 2012 12:16 AM, "Henning Thielemann" < lemming@henning-thielemann.de> wrote:
On Mon, 18 Jun 2012, Roman Leshchinskiy wrote:
There are type families, rank-n types, unboxed types and other goodies
deep in the guts of vector so the Storable part is very much GHC-specific. To be honest, I don't think being portable is feasible for high-performance code at the moment, the language standard simply doesn't have enough tools for this. Which is a shame, really.
I am not mainly interested in the efficient implementation. I am
completely ok with having the definition of (Vector a) in a separate package, such that it can be used by vector (GHC only) and storablevector (portable).
However, I have just looked into Vector.Storable and it looks like
data Vector a = Vector Int (ForeignPtr a)
I thought it was
data Vector a = Vector {len :: Int, allocated :: ForeignPtr a, start ::
Ptr a}
ByteString looks like:
data ByteString = PS {allocated :: ForeignPtr Word8, start, length ::
Int}
Both forms allow efficient slicing. How do you perform efficient 'take' and 'drop' ?
Slicing is done by directly updating the pointer in the ForeignPtr: {-# INLINE basicUnsafeSlice #-} basicUnsafeSlice i n (Vector _ fp) = Vector n (updPtr (`advancePtr` i) fp) {-# INLINE updPtr #-} updPtr :: (Ptr a -> Ptr a) -> ForeignPtr a -> ForeignPtr a updPtr f (ForeignPtr p c) = case f (Ptr p) of { Ptr q -> ForeignPtr q c } This saves an Int. Regards, Bas