Sven.Panne:
Am Freitag, 15. Mai 2009 06:37:22 schrieb Don Stewart:
timd:
On a related matter, I am using Data.Binary to serialise data from haskell for use from other languages. [...] [...] Yep, it's possible, just not portably so. Google for Data.Binary IEEE discussions.
I think this topic pops up over and over again, and the proposed "solutions" are no solutions at all, neither from a performance point of view, nor from an ease of use point of view. Proposing insane bit fiddling by hand when all one technically needs is often a "peek" or "poke" amounts to simply ignoring an API problem. ;-)
I think most problems can be fixed in a rather pragmatic way by adding a few functions to the binary package:
Add to Data.Binary.Builder:
putFloatIEEEbe :: Float -> Builder putDoubleIEEEbe :: Double -> Builder putFloatIEEEle :: Float -> Builder putDoubleIEEEle :: Double -> Builder putFloatIEEEhost :: Float -> Builder putDoubleIEEEhost :: Double -> Builder
Add to Data.Binary.Get:
getFloatIEEEbe :: Get Float getDoubleIEEEbe :: Get Double getFloatIEEEle :: Get Float getDoubleIEEEle :: Get Double getFloatIEEEhost :: Get Float getDoubleIEEEhost :: Get Double
Add to Data.Binary.Put:
putFloatIEEEbe :: Float -> Put putDoubleIEEEbe :: Double -> Put putFloatIEEEle :: Float -> Put putDoubleIEEEle :: Double -> Put putFloatIEEEhost :: Float -> Put putDoubleIEEEhost :: Double -> Put
The *host functions are basically peek/poke for most platforms. The *le/*be functions can use peek/poke if the endianess matches (compile time decision) *and* the alignment is OK for the given platform (runtime decision). Non-IEEE platforms always have to do the bit fiddling internally, but all this is hidden behind the above API.
IIRC I have proposed something similar 1-2 years ago, but I can't remember any reason why this hasn't been implemented. Any comments on the above functions?
Patches are welcome.
One final remarks: I think the low level functions of the binary package should really keep the notions of "endianess" and "alignment constraints" separate, something which isn't done currently: The *host functions have alignment restrictions, the *be/*le functions don't. There is no good reason for this non-orthogonality.
That seems reasonable. -- Don