On Mon, Sep 14, 2009 at 12:24 PM, minh thu <not...@gmail.com> wrote:
> Hi,
>
> I'd like to know if this should work:
>
> -- GHC coercion
> getFloat :: BHeader -> Get Float
> getFloat h =
> case endianness h of
> LittleEndian -> fmap (coerce . fromIntegral) getWord32le
> BigEndian -> fmap (coerce . fromIntegral) getWord32be
> where coerce (I32# x) = F# (unsafeCoerce# x)
>
> -- GHC coercion
> getDouble :: BHeader -> Get Double
> getDouble h =
> case endianness h of
> LittleEndian -> fmap (coerce . fromIntegral) getWord64le
> BigEndian -> fmap (coerce . fromIntegral) getWord64be
> where coerce (I64# x) = D# (unsafeCoerce# x)
>
> Loading this into ghci compiles fine (but I haven't try to parse
> data), but compiling with ghc (6.10.1 or 6.10.4) reports:
> /tmp/ghc1967_0/ghc1967_0.s: Assembler messages:
>
> /tmp/ghc1967_0/ghc1967_0.s:287:0:
> Error: bad register name `%fake0'
>
> /tmp/ghc1967_0/ghc1967_0.s:349:0:
> Error: bad register name `%fake0'
I think that a more reliable (though not very pretty) way to do the
casts is via pointer manipulation. Code like the following has worked
for me in the past:
getDouble :: Get Double
getDouble = fmap word2Double getWord64le
where
word2Double w = unsafePerformIO $ with w $ \p -> do
d :: CDouble <- peek (castPr p)
return (realToFrac d :: Double)
Best,
-Judah
_______________________________________________
Haskell-Cafe mailing list
Haskell-Cafe@haskell.org
http://www.haskell.org/mailman/listinfo/haskell-cafe
