    {-# LANGUAGE CPP, MagicHash, UnboxedTuples #-}
    -- |
    -- Module      : Data.Text.Unsafe
    -- Copyright   : (c) 2009, 2010, 2011 Bryan O'Sullivan
    -- License     : BSD-style
    -- Maintainer  : bos@serpentine.com
    -- Portability : portable
    --
    -- A module containing unsafe 'Text' operations, for very very careful
    -- use in heavily tested code.
    module Data.Text.Unsafe
        (
          inlineInterleaveST
        , inlinePerformIO
        , unsafeDupablePerformIO
        , Iter(..)
        , iter
        , iter_
        , reverseIter
        , reverseIter_
        , unsafeHead
        , unsafeTail
        , lengthWord16
        , takeWord16
        , dropWord16
        ) where

    #if defined(ASSERTS)
    import Control.Exception (assert)
    import GHC.Stack (HasCallStack)
    #endif
    import Data.Text.Internal.Encoding.Utf16 (chr2)
    import Data.Text.Internal (Text(..))
    import Data.Text.Internal.Unsafe (inlineInterleaveST, inlinePerformIO)
    import Data.Text.Internal.Unsafe.Char (unsafeChr)
    import qualified Data.Text.Array as A
    import GHC.IO (unsafeDupablePerformIO)

    -- | /O(1)/ A variant of 'head' for non-empty 'Text'. 'unsafeHead'
    -- omits the check for the empty case, so there is an obligation on
    -- the programmer to provide a proof that the 'Text' is non-empty.
    unsafeHead :: Text -> Char
    unsafeHead :: Text -> Char
    unsafeHead (Text Array
    arr Int
    off Int
    _len)
        | Word16
    m forall a. Ord a => a -> a -> Bool
    < Word16
    0xD800 Bool -> Bool -> Bool
    || Word16
    m forall a. Ord a => a -> a -> Bool
    > Word16
    0xDBFF = Word16 -> Char
    unsafeChr Word16
    m
        | Bool
    otherwise                = Word16 -> Word16 -> Char
    chr2 Word16
    m Word16
    n
        where m :: Word16
    m = Array -> Int -> Word16
    A.unsafeIndex Array
    arr Int
    off
              n :: Word16
    n = Array -> Int -> Word16
    A.unsafeIndex Array
    arr (Int
    offforall a. Num a => a -> a -> a
    +Int
    1)
    {-# INLINE unsafeHead #-}

    -- | /O(1)/ A variant of 'tail' for non-empty 'Text'. 'unsafeTail'
    -- omits the check for the empty case, so there is an obligation on
    -- the programmer to provide a proof that the 'Text' is non-empty.
    unsafeTail :: Text -> Text
    unsafeTail :: Text -> Text
    unsafeTail t :: Text
    t@(Text Array
    arr Int
    off Int
    len) =
    #if defined(ASSERTS)
        assert (d <= len) $
    #endif
        Array -> Int -> Int -> Text
    Text Array
    arr (Int
    offforall a. Num a => a -> a -> a
    +Int
    d) (Int
    lenforall a. Num a => a -> a -> a
    -Int
    d)
      where d :: Int
    d = Text -> Int -> Int
    iter_ Text
    t Int
    0
    {-# INLINE unsafeTail #-}

    data Iter = Iter {-# UNPACK #-} !Char {-# UNPACK #-} !Int

    -- | /O(1)/ Iterate (unsafely) one step forwards through a UTF-16
    -- array, returning the current character and the delta to add to give
    -- the next offset to iterate at.
    iter ::
    #if defined(ASSERTS)
      HasCallStack =>
    #endif
      Text -> Int -> Iter
    iter :: Text -> Int -> Iter
    iter (Text Array
    arr Int
    off Int
    _len) Int
    i
        | Word16
    m forall a. Ord a => a -> a -> Bool
    < Word16
    0xD800 Bool -> Bool -> Bool
    || Word16
    m forall a. Ord a => a -> a -> Bool
    > Word16
    0xDBFF = Char -> Int -> Iter
    Iter (Word16 -> Char
    unsafeChr Word16
    m) Int
    1
        | Bool
    otherwise                = Char -> Int -> Iter
    Iter (Word16 -> Word16 -> Char
    chr2 Word16
    m Word16
    n) Int
    2
      where m :: Word16
    m = Array -> Int -> Word16
    A.unsafeIndex Array
    arr Int
    j
            n :: Word16
    n = Array -> Int -> Word16
    A.unsafeIndex Array
    arr Int
    k
            j :: Int
    j = Int
    off forall a. Num a => a -> a -> a
    + Int
    i
            k :: Int
    k = Int
    j forall a. Num a => a -> a -> a
    + Int
    1
    {-# INLINE iter #-}

    -- | /O(1)/ Iterate one step through a UTF-16 array, returning the
    -- delta to add to give the next offset to iterate at.
    iter_ :: Text -> Int -> Int
    iter_ :: Text -> Int -> Int
    iter_ (Text Array
    arr Int
    off Int
    _len) Int
    i | Word16
    m forall a. Ord a => a -> a -> Bool
    < Word16
    0xD800 Bool -> Bool -> Bool
    || Word16
    m forall a. Ord a => a -> a -> Bool
    > Word16
    0xDBFF = Int
    1
                                | Bool
    otherwise                = Int
    2
      where m :: Word16
    m = Array -> Int -> Word16
    A.unsafeIndex Array
    arr (Int
    offforall a. Num a => a -> a -> a
    +Int
    i)
    {-# INLINE iter_ #-}

    -- | /O(1)/ Iterate one step backwards through a UTF-16 array,
    -- returning the current character and the delta to add (i.e. a
    -- negative number) to give the next offset to iterate at.
    reverseIter :: Text -> Int -> (Char,Int)
    reverseIter :: Text -> Int -> (Char, Int)
    reverseIter (Text Array
    arr Int
    off Int
    _len) Int
    i
        | Word16
    m forall a. Ord a => a -> a -> Bool
    < Word16
    0xDC00 Bool -> Bool -> Bool
    || Word16
    m forall a. Ord a => a -> a -> Bool
    > Word16
    0xDFFF = (Word16 -> Char
    unsafeChr Word16
    m, -Int
    1)
        | Bool
    otherwise                = (Word16 -> Word16 -> Char
    chr2 Word16
    n Word16
    m,    -Int
    2)
      where m :: Word16
    m = Array -> Int -> Word16
    A.unsafeIndex Array
    arr Int
    j
            n :: Word16
    n = Array -> Int -> Word16
    A.unsafeIndex Array
    arr Int
    k
            j :: Int
    j = Int
    off forall a. Num a => a -> a -> a
    + Int
    i
            k :: Int
    k = Int
    j forall a. Num a => a -> a -> a
    - Int
    1
    {-# INLINE reverseIter #-}

    -- | /O(1)/ Iterate one step backwards through a UTF-16 array,
    -- returning the delta to add (i.e. a negative number) to give the
    -- next offset to iterate at.
    --
    -- @since 1.1.1.0
    reverseIter_ :: Text -> Int -> Int
    reverseIter_ :: Text -> Int -> Int
    reverseIter_ (Text Array
    arr Int
    off Int
    _len) Int
    i
        | Word16
    m forall a. Ord a => a -> a -> Bool
    < Word16
    0xDC00 Bool -> Bool -> Bool
    || Word16
    m forall a. Ord a => a -> a -> Bool
    > Word16
    0xDFFF = -Int
    1
        | Bool
    otherwise                = -Int
    2
      where m :: Word16
    m = Array -> Int -> Word16
    A.unsafeIndex Array
    arr (Int
    offforall a. Num a => a -> a -> a
    +Int
    i)
    {-# INLINE reverseIter_ #-}

    -- | /O(1)/ Return the length of a 'Text' in units of 'Word16'.  This
    -- is useful for sizing a target array appropriately before using
    -- 'unsafeCopyToPtr'.
    lengthWord16 :: Text -> Int
    lengthWord16 :: Text -> Int
    lengthWord16 (Text Array
    _arr Int
    _off Int
    len) = Int
    len
    {-# INLINE lengthWord16 #-}

    -- | /O(1)/ Unchecked take of 'k' 'Word16's from the front of a 'Text'.
    takeWord16 :: Int -> Text -> Text
    takeWord16 :: Int -> Text -> Text
    takeWord16 Int
    k (Text Array
    arr Int
    off Int
    _len) = Array -> Int -> Int -> Text
    Text Array
    arr Int
    off Int
    k
    {-# INLINE takeWord16 #-}

    -- | /O(1)/ Unchecked drop of 'k' 'Word16's from the front of a 'Text'.
    dropWord16 :: Int -> Text -> Text
    dropWord16 :: Int -> Text -> Text
    dropWord16 Int
    k (Text Array
    arr Int
    off Int
    len) = Array -> Int -> Int -> Text
    Text Array
    arr (Int
    offforall a. Num a => a -> a -> a
    +Int
    k) (Int
    lenforall a. Num a => a -> a -> a
    -Int
    k)
    {-# INLINE dropWord16 #-}