BigEndian.hs

-- | This is drop-in replacement for the read, write, and index functions
-- present in @Data.Primitive.Ptr@. While the functions from those modules
-- use native byte order, the functions in this one use big-endian byte order
-- (most significant byte first).
module Data.Primitive.Ptr.BigEndian
  ( -- * Aligned
    writeOffPtr
  , readOffPtr
  , indexOffPtr
  ) where

import Data.Primitive (Prim)
import Data.Primitive.Ptr (Ptr)
import Control.Monad.Primitive (PrimMonad)
import System.ByteOrder (Bytes,toBigEndian,fromBigEndian)
import qualified Data.Primitive.Ptr as PM

-- | Write a primitive value to the pointer. The offset is given
-- in elements of type @a@ rather than in bytes. The most significant
-- byte in the value comes first.
writeOffPtr :: (PrimMonad m, Prim a, Bytes a) => Ptr a -> Int -> a -> m ()
writeOffPtr arr ix v = PM.writeOffPtr arr ix (toBigEndian v)

-- | Read a primitive value from the pointer, interpreting the first
-- byte as the most significant one. The offset is given in elements of
-- type @a@ rather than in bytes.
readOffPtr :: (PrimMonad m, Prim a, Bytes a) => Ptr a -> Int -> m a
readOffPtr arr ix = fromBigEndian <$> PM.readOffPtr arr ix

-- | Read a primitive value from the pointer, interpreting the first
-- byte as the most significant one. The offset is given in elements of
-- type @a@ rather than in bytes.
indexOffPtr :: (Prim a, Bytes a) => Ptr a -> Int -> a
indexOffPtr arr ix = fromBigEndian (PM.indexOffPtr arr ix)