System.ByteOrder

This module offers an interface to portably work with byte arrays whose contents are known to be of a fixed endianness. There are two ways to use this module:

• Untyped Conversions: The functions toBigEndian, toLittleEndian, fromBigEndian, and fromLittleEndian convert between native-endian words and big/little-endian words. The word resulting from to(Big|Little)Endian should be written to a primitive byte array or a pointer afterwards. (There is no other purpose of such a conversion.) Similarly, the argument to from(Big|Little)Endian should be a word that was read from a primitive byte array or a pointer. This interface is useful when serializing or deserializing a data structure with fields of varying sizes.
• Typed Conversions: The type Fixed provides a convenient type-directed interface to working with arrays of homogenous words. This interface is easier to use and should be preferred when possible.

The example at the bottom of this page demonstrates how to use the type-directed interface.

Types

data ByteOrder

Byte ordering.

Constructors

BigEndian

most-significant-byte occurs in lowest address.

LittleEndian

least-significant-byte occurs in lowest address.

Instances

Bounded ByteOrder

Since: base-4.11.0.0

Defined in GHC.ByteOrder

Methods

minBound :: ByteOrder

maxBound :: ByteOrder

Enum ByteOrder

Since: base-4.11.0.0

Defined in GHC.ByteOrder

Methods

succ :: ByteOrder -> ByteOrder

pred :: ByteOrder -> ByteOrder

toEnum :: Int -> ByteOrder

fromEnum :: ByteOrder -> Int

enumFrom :: ByteOrder -> [ByteOrder]

enumFromThen :: ByteOrder -> ByteOrder -> [ByteOrder]

enumFromTo :: ByteOrder -> ByteOrder -> [ByteOrder]

enumFromThenTo :: ByteOrder -> ByteOrder -> ByteOrder -> [ByteOrder]

Eq ByteOrder

Since: base-4.11.0.0

Defined in GHC.ByteOrder

Methods

(==) :: ByteOrder -> ByteOrder -> Bool

(/=) :: ByteOrder -> ByteOrder -> Bool

Ord ByteOrder

Since: base-4.11.0.0

Defined in GHC.ByteOrder

Methods

compare :: ByteOrder -> ByteOrder -> Ordering

(<) :: ByteOrder -> ByteOrder -> Bool

(<=) :: ByteOrder -> ByteOrder -> Bool

(>) :: ByteOrder -> ByteOrder -> Bool

(>=) :: ByteOrder -> ByteOrder -> Bool

max :: ByteOrder -> ByteOrder -> ByteOrder

min :: ByteOrder -> ByteOrder -> ByteOrder

Read ByteOrder

Since: base-4.11.0.0

Defined in GHC.ByteOrder

Methods

readsPrec :: Int -> ReadS ByteOrder

readList :: ReadS [ByteOrder]

readPrec :: ReadPrec ByteOrder

readListPrec :: ReadPrec [ByteOrder]

Show ByteOrder

Since: base-4.11.0.0

Defined in GHC.ByteOrder

Methods

showsPrec :: Int -> ByteOrder -> ShowS

show :: ByteOrder -> String

showList :: [ByteOrder] -> ShowS

newtype Fixed :: ByteOrder -> Type -> Type where

A word whose byte order is specified (not platform dependent) when working with Prim, Storable, and PrimUnaligned (this last instance is provided alongside the typeclass itself in the primitive-unaligned library).

Constructors

Fixed

Fields

• :: forall (b :: ByteOrder) (a :: Type). { getFixed :: a
•    } -> Fixed b a

Instances

Enum a => Enum (Fixed b a)

Defined in System.ByteOrder

Methods

succ :: Fixed b a -> Fixed b a

pred :: Fixed b a -> Fixed b a

toEnum :: Int -> Fixed b a

fromEnum :: Fixed b a -> Int

enumFrom :: Fixed b a -> [Fixed b a]

enumFromThen :: Fixed b a -> Fixed b a -> [Fixed b a]

enumFromTo :: Fixed b a -> Fixed b a -> [Fixed b a]

enumFromThenTo :: Fixed b a -> Fixed b a -> Fixed b a -> [Fixed b a]

Eq a => Eq (Fixed b a)

Defined in System.ByteOrder

Methods

(==) :: Fixed b a -> Fixed b a -> Bool

(/=) :: Fixed b a -> Fixed b a -> Bool

Integral a => Integral (Fixed b a)

Defined in System.ByteOrder

Methods

quot :: Fixed b a -> Fixed b a -> Fixed b a

rem :: Fixed b a -> Fixed b a -> Fixed b a

div :: Fixed b a -> Fixed b a -> Fixed b a

mod :: Fixed b a -> Fixed b a -> Fixed b a

quotRem :: Fixed b a -> Fixed b a -> (Fixed b a, Fixed b a)

divMod :: Fixed b a -> Fixed b a -> (Fixed b a, Fixed b a)

toInteger :: Fixed b a -> Integer

Num a => Num (Fixed b a)

Defined in System.ByteOrder

Methods

(+) :: Fixed b a -> Fixed b a -> Fixed b a

(-) :: Fixed b a -> Fixed b a -> Fixed b a

(*) :: Fixed b a -> Fixed b a -> Fixed b a

negate :: Fixed b a -> Fixed b a

abs :: Fixed b a -> Fixed b a

signum :: Fixed b a -> Fixed b a

fromInteger :: Integer -> Fixed b a

Ord a => Ord (Fixed b a)

Defined in System.ByteOrder

Methods

compare :: Fixed b a -> Fixed b a -> Ordering

(<) :: Fixed b a -> Fixed b a -> Bool

(<=) :: Fixed b a -> Fixed b a -> Bool

(>) :: Fixed b a -> Fixed b a -> Bool

(>=) :: Fixed b a -> Fixed b a -> Bool

max :: Fixed b a -> Fixed b a -> Fixed b a

min :: Fixed b a -> Fixed b a -> Fixed b a

Real a => Real (Fixed b a)

Defined in System.ByteOrder

Methods

toRational :: Fixed b a -> Rational

(FixedOrdering b, Storable a, Bytes a) => Storable (Fixed b a)

Defined in System.ByteOrder

Methods

sizeOf :: Fixed b a -> Int

alignment :: Fixed b a -> Int

peekElemOff :: Ptr (Fixed b a) -> Int -> IO (Fixed b a)

pokeElemOff :: Ptr (Fixed b a) -> Int -> Fixed b a -> IO ()

peekByteOff :: Ptr b0 -> Int -> IO (Fixed b a)

pokeByteOff :: Ptr b0 -> Int -> Fixed b a -> IO ()

peek :: Ptr (Fixed b a) -> IO (Fixed b a)

poke :: Ptr (Fixed b a) -> Fixed b a -> IO ()

(FixedOrdering b, Prim a, Bytes a) => Prim (Fixed b a)

Defined in System.ByteOrder

Methods

sizeOf# :: Fixed b a -> Int#

alignment# :: Fixed b a -> Int#

indexByteArray# :: ByteArray# -> Int# -> Fixed b a

readByteArray# :: MutableByteArray# s -> Int# -> State# s -> (#State# s, Fixed b a#)

writeByteArray# :: MutableByteArray# s -> Int# -> Fixed b a -> State# s -> State# s

setByteArray# :: MutableByteArray# s -> Int# -> Int# -> Fixed b a -> State# s -> State# s

indexOffAddr# :: Addr# -> Int# -> Fixed b a

readOffAddr# :: Addr# -> Int# -> State# s -> (#State# s, Fixed b a#)

writeOffAddr# :: Addr# -> Int# -> Fixed b a -> State# s -> State# s

setOffAddr# :: Addr# -> Int# -> Int# -> Fixed b a -> State# s -> State# s

(FixedOrdering b, PrimUnaligned a, Bytes a) => PrimUnaligned (Fixed b a)

Defined in System.ByteOrder

Methods

indexUnalignedByteArray# :: ByteArray# -> Int# -> Fixed b a

readUnalignedByteArray# :: MutableByteArray# s -> Int# -> State# s -> (#State# s, Fixed b a#)

writeUnalignedByteArray# :: MutableByteArray# s -> Int# -> Fixed b a -> State# s -> State# s

Classes

class Bytes a

Types that are represented as a fixed-sized word. For these types, the bytes can be swapped. The instances of this class use byteswapping primitives and compile-time knowledge of native endianness to provide portable endianness conversion functions.

Minimal complete definition

toBigEndian, toLittleEndian

Instances

Bytes Int8

Defined in System.ByteOrder.Class

Methods

toBigEndian :: Int8 -> Int8

toLittleEndian :: Int8 -> Int8

Bytes Int16

Defined in System.ByteOrder.Class

Methods

toBigEndian :: Int16 -> Int16

toLittleEndian :: Int16 -> Int16

Bytes Int32

Defined in System.ByteOrder.Class

Methods

toBigEndian :: Int32 -> Int32

toLittleEndian :: Int32 -> Int32

Bytes Int64

Defined in System.ByteOrder.Class

Methods

toBigEndian :: Int64 -> Int64

toLittleEndian :: Int64 -> Int64

Bytes Word

Defined in System.ByteOrder.Class

Methods

toBigEndian :: Word -> Word

toLittleEndian :: Word -> Word

Bytes Word8

Defined in System.ByteOrder.Class

Methods

toBigEndian :: Word8 -> Word8

toLittleEndian :: Word8 -> Word8

Bytes Word16

Defined in System.ByteOrder.Class

Methods

toBigEndian :: Word16 -> Word16

toLittleEndian :: Word16 -> Word16

Bytes Word32

Defined in System.ByteOrder.Class

Methods

toBigEndian :: Word32 -> Word32

toLittleEndian :: Word32 -> Word32

Bytes Word64

Defined in System.ByteOrder.Class

Methods

toBigEndian :: Word64 -> Word64

toLittleEndian :: Word64 -> Word64

class FixedOrdering (b :: ByteOrder)

A byte order that can be interpreted as a conversion function. This class is effectively closed. The only instances are for BigEndian and LittleEndian. It is not possible to write more instances since there are no other inhabitants of ByteOrder.

Minimal complete definition

toFixedEndian

Instances

FixedOrdering LittleEndian

Defined in System.ByteOrder.Class

Methods

toFixedEndian :: Bytes a => a -> a

FixedOrdering BigEndian

Defined in System.ByteOrder.Class

Methods

toFixedEndian :: Bytes a => a -> a

Conversion

toBigEndian :: Bytes a => a -> a

Convert from a native-endian word to a big-endian word.

toLittleEndian :: Bytes a => a -> a

Convert from a native-endian word to a little-endian word.

fromBigEndian :: Bytes a => a -> a

Convert from a big-endian word to a native-endian word.

fromLittleEndian :: Bytes a => a -> a

Convert from a little-endian word to a native-endian word.

System Byte Order

targetByteOrder :: ByteOrder

The byte ordering of the target machine.

Example

Suppose there is a protocol for aggregating numbers that uses stream sockets for communication. The protocol interprets all numbers as unsigned. It is described as follows:

1. The client sends the server a little-endian 16-bit number N. This is how many numbers will follow.
2. The client sends N little-endian 64-bit numbers to the server.
3. The server responds with two little-endian 64-bit numbers: the sum and the product of the N numbers it received.

Assume the existence of a send and receive that block until the total number of requested bytes have been handled. They both work on their argument arrays starting at index zero, which ensures that any 2-byte, 4-byte, or 8-byte types will be aligned properly. (GHC always machine-word aligns the payload of a byte array.) Additionally, assume the typed and untyped functions that convert between PrimArray and ByteArray by changing out the data constructor.

send :: Socket -> ByteArray -> IO ()
receive :: Socket -> Int -> IO ByteArray
typed :: ByteArray -> PrimArray a
untyped :: PrimArray a -> ByteArray

For simplicity, all error-handling is omitted. With the type-directed interface, the server is implemented as:

import Data.Primitive.ByteArray
import Data.Primitive.PrimArray
import System.ByteOrder

server :: Socket -> IO a
server sckt = forever $ do
  totalByteArray <- receive sckt 2
  let totalPrimArray = typed totalByteArray :: PrimArray (Fixed 'LittleEndian Word16)
  let Fixed total = indexPrimArray totalPrimArray 0
  numberByteArray <- receive sckt (8 * fromIntegral @Word16 @Int total)
  let (sum,prod) = foldlPrimArray'
        (\(!sumN,!prodN) (Fixed n) -> (sumN + n, prodN * n))
        (0,1)
        (typed numberByteArray :: PrimArray (Fixed 'LittleEndian Word64))
  reply :: MutablePrimArray RealWorld (Fixed 'LittleEndian Word64) <- newPrimArray 2
  writePrimArray reply 0 (Fixed sum)
  writePrimArray reply 1 (Fixed prod)
  send sckt . untyped =<< unsafeFreezePrimArray reply

Not every explicit type annotation above is needed. Some are provided for the reader's benefit. As long as the user ensures that the typed primitive arrays use Fixed in their element types, the endianness conversions are guaranteed to be correct.