Question

我正在使用来自 Data.Binary 的获取 monad，从包含带符号16位整数的二进制文件中读取结构。我目前的代码如下：

data DetectorStats = DetectorStats Int16 Word8 Word8
                     Word8 Int16 Version Int16 
                     deriving Show

getDetectorStats :: Get DetectorStats
getDetectorStats = do
  productNumber <- getWord16be
  bitPerCoordinate <- getWord8
  energyCapability <- getWord8
  timingCapability <- getWord8
  clockFrequency <- getWord16be
  serialNumber <- getWord16be
  return (DetectorStats (unsafeCoerce productNumber )
                        bitPerCoordinate
                        energyCapability 
                        timingCapability
                        (unsafeCoerce clockFrequency)
                        firmwareVersion
                        (unsafeCoerce serialNumber))

我对使用 unsafeCoerce 感到不满意，但似乎没有办法直接读取 Int16 ，也没有办法转换 Word16 进入 Int16 。有没有更好的方法来处理这个？

Answer 1

fromIntegral 会将Word16转换为Int16。但是，您必须检查它是否得到了您预期的签名结果。

Answer 2

Data.Convertible包应该可以满足您的要求。

例如，要从Word16转换为Int16：

> (convert (6 :: Word16)) :: Int16
6

Answer 3

在Stephen的答案的基础上，这是一个实现Int8，Int16和Int32的get和put函数，类似于Word8，Word16和Word32的现有函数。我还没有要求Int64或Host-endian支持，但可以添加这些：

{-# LANGUAGE RecordWildCards #-}
module GetAndPutForInt
( getInt8
, getInt16be
, getInt16le
, getInt32be
, getInt32le
, putInt8
, putInt16be
, putInt16le
, putInt32be
, putInt32le
) where

import Data.Binary
import Data.Binary.Get
import Data.Binary.Put

import Data.Int
import Data.Word

import qualified Data.ByteString.Lazy as B

getInt8 :: Get Int8
getInt8 = do a <- getWord8
             return $ fromIntegral a
getInt16be :: Get Int16
getInt16be = do a <- getWord16be
                return $ fromIntegral a
getInt16le :: Get Int16
getInt16le = do a <- getWord16le
                return $ fromIntegral a
getInt32be :: Get Int32
getInt32be = do a <- getWord32be
                return $ fromIntegral a
getInt32le :: Get Int32
getInt32le = do a <- getWord32le
                return $ fromIntegral a

putInt8 :: Int8 -> Put
putInt8 i = putWord8 ((fromIntegral i) :: Word8)
putInt16be :: Int16 -> Put
putInt16be i = putWord16be ((fromIntegral i) :: Word16)
putInt16le :: Int16 -> Put
putInt16le i = putWord16le ((fromIntegral i) :: Word16)
putInt32be :: Int32 -> Put
putInt32be i = putWord32be ((fromIntegral i) :: Word32)
putInt32le :: Int32 -> Put
putInt32le i = putWord32le ((fromIntegral i) :: Word32)

data TestType = TestType
    { a :: Int16
    , b :: Int16
    } deriving (Show, Eq)

instance Binary TestType where
    put TestType{..} =
      do putInt16be a
         putInt16le b
    get = do a <- getInt16be
             b <- getInt16le
             return TestType{..}

main :: IO ()
main = do
    putStrLn "Supplies Get and Put support to Int8, Int16 etc. types as Data.Binary.Get and Data.Binary.Push do for Word8, Word 16 etc."
    putStrLn ""
    putStrLn "Test data in bytes:"
    print bytes
    putStrLn ""
    putStrLn "As TestType:"
    print (decode bytes :: TestType)
    putStrLn ""
    putStrLn "Back to bytes:"
    print $ (encode ((decode bytes) :: TestType))
  where
    bytes = B.pack $ concat $ replicate 2 [0xCD,0xEF]

在没有unsafeCoerce的情况下处理Haskell中的签名二进制数据

3 个答案: