arrays - IOUArray to ByteSring, as quickly as possible -

i need mutate elements in fixed size array of word8 quickly. purpose using iouarray. need send array on websocket connection. function sendbinarydata websockets package requires bytestring. need convert 1 representation other. using function currently:

arraytobs :: iouarray int word8 -> io (bs.bytestring) arraytobs = (fmap bs.pack) . getelems 

this function converts elements of array [word8] before packing list bytestring, , profiling can see quite slow. wondering if there way speed function, or possibly send array on websocket connection directly?

the array using is:

size = 1000; numbytes = size * size * 4  newbuffer :: io (iouarray int word8) newbuffer = newarray (0, numbytes) 200 :: io (iouarray int word8) 

and except performance report:

cost centre module src                        %time %alloc  arraytobs   lib    src/lib.hs:28:1-37          88.1   99.0 newbuffer   lib    src/lib.hs:(23,1)-(25,12)    9.9    0.8 

ideally arraytobs faster creating array. if change size 100:

cost centre         module                          src                                                %time %alloc  arraytobs           lib                             src/lib.hs:21:1-37                           100.0   86.1 mkencodetable.table data.bytestring.base64.internal data/bytestring/base64/internal.hs:105:5-75    0.0    8.0 mkencodetable.ix    data.bytestring.base64.internal data/bytestring/base64/internal.hs:104:5-43    0.0    1.1 

disclaimer: i'm not familiar these low level primitives might unsafe in cases.

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you @ least need copy data on once since, @user2407038 remarks, underlying data stored in iouarray unpinned array, can't count on ghc not moving array around. reverse direction (bytestring ioarray) possible without copy.

{-# language unboxedtuples, magichash #-}  import data.bytestring.internal (bytestring(..)) import data.array.io.internals  (iouarray(..)) import data.array.base          (stuarray(..))  import foreign.foreignptr (mallocforeignptrbytes, withforeignptr) import ghc.io             (io(..)) import ghc.exts           (copymutablebytearraytoaddr#, ptr(..), int(..))  arraytobs :: iouarray int word8 -> io bytestring arraytobs (iouarray (stuarray _ _ n@(i# n') mutbytearr)) =   bytes <- mallocforeignptrbytes n   withforeignptr bytes $ \(ptr addr) -> io $ \state ->     (# copymutablebytearraytoaddr# mutbytearr 0# addr n' state, () #)   pure (ps bytes 0 n) 

here test of working (remember ascii code 'a' 65):

ghci> iou <- newlistarray (-2,9) [65,67..] :: io (iouarray int word8) ghci> arraytobs iou "acegikmoqsuw"