[Haskell-cafe] Endian conversion
joelr1 at gmail.com
Thu Oct 6 04:04:26 EDT 2005
Regarding NewBinary... I think my challenge is how to add endian-
conversion without duplicating all the put and get methods from
I would still use that bit of TH code to figure out whether my
platform is big or little endian. I don't care about cross-
compilation and what that code does is analogous to #ifdef ...
#define LITTLE_ENDIAN ... #endif, etc.
I'm looking for architectural suggestions, though. Should I define
LittleEndian Word32, BigEndian Word16, etc. or should I have Endian
Word32 Big, Endian Word16 Little, etc.
On Oct 5, 2005, at 11:42 AM, Udo Stenzel wrote:
>>> Why don't you pull out 4 bytes and assemble them manually?
> To that I'd like to add a snippet from NewBinary itself:
> | instance Binary Word32 where
> | put_ h w = do
> | putByte h (fromIntegral (w `shiftR` 24))
> | putByte h (fromIntegral ((w `shiftR` 16) .&. 0xff))
> | putByte h (fromIntegral ((w `shiftR` 8) .&. 0xff))
> | putByte h (fromIntegral (w .&. 0xff))
> | get h = do
> | w1 <- getWord8 h
> | w2 <- getWord8 h
> | w3 <- getWord8 h
> | w4 <- getWord8 h
> | return $! ((fromIntegral w1 `shiftL` 24) .|.
> | (fromIntegral w2 `shiftL` 16) .|.
> | (fromIntegral w3 `shiftL` 8) .|.
> | (fromIntegral w4))
> This obviously writes a Word32 in big endian format, also known as
> "network byte order", and doesn't care how the host platform stores
> integers. No need for `hton' and `ntoh'. To convert it to write
> endian, just copy it and reorder some lines. (But I think, writing LE
> integers with no good reason and without an enclosing protocol that
> explicitly declares them (like IIOP) is a bad idea.)
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