On Jan 9, 2008 5:18 AM, allan
Essentially then, is there anyone that can write my 'putDouble' function or give some hint as to how I might do it. For the moment assume that I'm not really concerned with portability across platforms at least for the time being (I certainly don't think that the C program I'm attempting to communicate with is particularly portable anyway).
I happen to have the reverse functions lying around which might be some help in doing this. They aren't terribly beautiful, but they'll take an IEEE double or float from a Bytestring and return the value + the remaining ByteString. (They aren't very well tested, but they have been found to mostly work). ddouble :: BS.ByteString -> (Double, BS.ByteString) ddouble bytes = (encodeFloat fraction $ fromIntegral exp, rest) where fraction = sign * fromIntegral ((n .&. 0xfffffffffffff) .|. (if rawExp > 0 then 0x10000000000000 else 0)) sign = if n `shiftR` 63 == 0 then 1 else -1 exp = rawExp - (1023 + 52) rawExp = (n `shiftR` 52) .&. 0x7ff (b, rest) = BS.splitAt 8 bytes n :: Word64 n = foldl1 (.|.) $ map (\(s, v) -> (fromIntegral v) `shiftL` s) $ zip [0,8..56] $ BS.unpack b dfloat :: BS.ByteString -> (Float, BS.ByteString) dfloat bytes = (encodeFloat fraction $ fromIntegral exp, rest) where fraction = sign * fromIntegral ((n .&. 0x7fffff) .|. (if rawExp > 0 then 0x800000 else 0)) sign = if n `shiftR` 31 == 0 then 1 else -1 exp = rawExp - (127 + 23) rawExp = (n `shiftR` 23) .&. 0xff (b, rest) = BS.splitAt 4 bytes n :: Word32 n = foldl1 (.|.) $ map (\(s, v) -> (fromIntegral v) `shiftL` s) $ zip [0, 8, 16, 24] $ BS.unpack b AGL -- Adam Langley agl@imperialviolet.org http://www.imperialviolet.org 650-283-9641