\begin{code}
+{-# LANGUAGE NoImplicitPrelude, NoBangPatterns, MagicHash, UnboxedTuples #-}
{-# OPTIONS_GHC -funbox-strict-fields #-}
-{-# LANGUAGE NoImplicitPrelude, NoBangPatterns #-}
{-# OPTIONS_HADDOCK hide #-}
+
-----------------------------------------------------------------------------
-- |
-- Module : GHC.Arr
-- An implementation is entitled to assume the following laws about these
-- operations:
--
--- * @'inRange' (l,u) i == 'elem' i ('range' (l,u))@
+-- * @'inRange' (l,u) i == 'elem' i ('range' (l,u))@ @ @
--
-- * @'range' (l,u) '!!' 'index' (l,u) i == i@, when @'inRange' (l,u) i@
--
--- * @'map' ('index' (l,u)) ('range' (l,u))) == [0..'rangeSize' (l,u)-1]@
+-- * @'map' ('index' (l,u)) ('range' (l,u))) == [0..'rangeSize' (l,u)-1]@ @ @
--
--- * @'rangeSize' (l,u) == 'length' ('range' (l,u))@
+-- * @'rangeSize' (l,u) == 'length' ('range' (l,u))@ @ @
--
-- Minimal complete instance: 'range', 'index' and 'inRange'.
--
unsafeRangeSize :: (a,a) -> Int
-- Must specify one of index, unsafeIndex
+
+ -- 'index' is typically over-ridden in instances, with essentially
+ -- the same code, but using indexError instead of hopelessIndexError
+ -- Reason: we have 'Show' at the instances
+ {-# INLINE index #-} -- See Note [Inlining index]
index b i | inRange b i = unsafeIndex b i
- | otherwise = error "Error in array index"
+ | otherwise = hopelessIndexError
+
unsafeIndex b i = index b i
rangeSize b@(_l,h) | inRange b h = unsafeIndex b h + 1
%* *
%*********************************************************
+Note [Inlining index]
+~~~~~~~~~~~~~~~~~~~~~
+We inline the 'index' operation,
+
+ * Partly because it generates much faster code
+ (although bigger); see Trac #1216
+
+ * Partly because it exposes the bounds checks to the simplifier which
+ might help a big.
+
+If you make a per-instance index method, you may consider inlining it.
+
+Note [Double bounds-checking of index values]
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+When you index an array, a!x, there are two possible bounds checks we might make:
+
+ (A) Check that (inRange (bounds a) x) holds.
+
+ (A) is checked in the method for 'index'
+
+ (B) Check that (index (bounds a) x) lies in the range 0..n,
+ where n is the size of the underlying array
+
+ (B) is checked in the top-level function (!), in safeIndex.
+
+Of course it *should* be the case that (A) holds iff (B) holds, but that
+is a property of the particular instances of index, bounds, and inRange,
+so GHC cannot guarantee it.
+
+ * If you do (A) and not (B), then you might get a seg-fault,
+ by indexing at some bizarre location. Trac #1610
+
+ * If you do (B) but not (A), you may get no complaint when you index
+ an array out of its semantic bounds. Trac #2120
+
+At various times we have had (A) and not (B), or (B) and not (A); both
+led to complaints. So now we implement *both* checks (Trac #2669).
+
+For 1-d, 2-d, and 3-d arrays of Int we have specialised instances to avoid this.
+
+Note [Out-of-bounds error messages]
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+The default method for 'index' generates hoplelessIndexError, because
+Ix doesn't have Show as a superclass. For particular base types we
+can do better, so we override the default method for index.
+
\begin{code}
--- abstract these errors from the relevant index functions so that
+-- Abstract these errors from the relevant index functions so that
-- the guts of the function will be small enough to inline.
{-# NOINLINE indexError #-}
showString " out of range " $
showParen True (showsPrec 0 rng) "")
+hopelessIndexError :: Int -- Try to use 'indexError' instead!
+hopelessIndexError = error "Error in array index"
+
----------------------------------------------------------------------
instance Ix Char where
{-# INLINE range #-}
{-# INLINE unsafeIndex #-}
unsafeIndex (m,_n) i = fromEnum i - fromEnum m
+ {-# INLINE index #-} -- See Note [Out-of-bounds error messages]
+ -- and Note [Inlining index]
index b i | inRange b i = unsafeIndex b i
| otherwise = indexError b i "Char"
{-# INLINE unsafeIndex #-}
unsafeIndex (m,_n) i = i - m
+ {-# INLINE index #-} -- See Note [Out-of-bounds error messages]
+ -- and Note [Inlining index]
index b i | inRange b i = unsafeIndex b i
| otherwise = indexError b i "Int"
{-# INLINE unsafeIndex #-}
unsafeIndex (m,_n) i = fromInteger (i - m)
+ {-# INLINE index #-} -- See Note [Out-of-bounds error messages]
+ -- and Note [Inlining index]
index b i | inRange b i = unsafeIndex b i
| otherwise = indexError b i "Integer"
{-# INLINE unsafeIndex #-}
unsafeIndex (l,_) i = fromEnum i - fromEnum l
+ {-# INLINE index #-} -- See Note [Out-of-bounds error messages]
+ -- and Note [Inlining index]
index b i | inRange b i = unsafeIndex b i
| otherwise = indexError b i "Bool"
{-# INLINE unsafeIndex #-}
unsafeIndex (l,_) i = fromEnum i - fromEnum l
+ {-# INLINE index #-} -- See Note [Out-of-bounds error messages]
+ -- and Note [Inlining index]
index b i | inRange b i = unsafeIndex b i
| otherwise = indexError b i "Ordering"
unsafeIndex ((), ()) () = 0
{-# INLINE inRange #-}
inRange ((), ()) () = True
- {-# INLINE index #-}
+
+ {-# INLINE index #-} -- See Note [Inlining index]
index b i = unsafeIndex b i
----------------------------------------------------------------------
-- | The type of immutable non-strict (boxed) arrays
-- with indices in @i@ and elements in @e@.
--- The Int is the number of elements in the Array.
data Ix i => Array i e
= Array !i -- the lower bound, l
!i -- the upper bound, u
--
-- Because the indices must be checked for these errors, 'array' is
-- strict in the bounds argument and in the indices of the association
--- list, but nonstrict in the values. Thus, recurrences such as the
+-- list, but non-strict in the values. Thus, recurrences such as the
-- following are possible:
--
-- > a = array (1,100) ((1,1) : [(i, i * a!(i-1)) | i <- [2..100]])
{-# INLINE fill #-}
fill :: MutableArray# s e -> (Int, e) -> STRep s a -> STRep s a
-fill marr# (I# i#, e) next s1# =
- case writeArray# marr# i# e s1# of { s2# ->
- next s2# }
+-- NB: put the \s after the "=" so that 'fill'
+-- inlines when applied to three args
+fill marr# (I# i#, e) next
+ = \s1# -> case writeArray# marr# i# e s1# of
+ s2# -> next s2#
{-# INLINE done #-}
done :: Ix i => i -> i -> Int -> MutableArray# s e -> STRep s (Array i e)
-done l u n marr# s1# =
- case unsafeFreezeArray# marr# s1# of
- (# s2#, arr# #) -> (# s2#, Array l u n arr# #)
+-- See NB on 'fill'
+done l u n marr#
+ = \s1# -> case unsafeFreezeArray# marr# s1# of
+ (# s2#, arr# #) -> (# s2#, Array l u n arr# #)
-- This is inefficient and I'm not sure why:
-- listArray (l,u) es = unsafeArray (l,u) (zip [0 .. rangeSize (l,u) - 1] es)
{-# INLINE safeRangeSize #-}
safeRangeSize :: Ix i => (i, i) -> Int
safeRangeSize (l,u) = let r = rangeSize (l, u)
- in if r < 0 then error "Negative range size"
+ in if r < 0 then negRange
else r
-{-# INLINE safeIndex #-}
+-- Don't inline this error message everywhere!!
+negRange :: Int -- Uninformative, but Ix does not provide Show
+negRange = error "Negative range size"
+
+{-# INLINE[1] safeIndex #-}
+-- See Note [Double bounds-checking of index values]
+-- Inline *after* (!) so the rules can fire
safeIndex :: Ix i => (i, i) -> Int -> i -> Int
safeIndex (l,u) n i = let i' = index (l,u) i
in if (0 <= i') && (i' < n)
then i'
- else error ("Error in array index; " ++ show i' ++
- " not in range [0.." ++ show n ++ ")")
+ else badSafeIndex i' n
+
+-- See Note [Double bounds-checking of index values]
+{-# RULES
+"safeIndex/I" safeIndex = lessSafeIndex :: (Int,Int) -> Int -> Int -> Int
+"safeIndex/(I,I)" safeIndex = lessSafeIndex :: ((Int,Int),(Int,Int)) -> Int -> (Int,Int) -> Int
+"safeIndex/(I,I,I)" safeIndex = lessSafeIndex :: ((Int,Int,Int),(Int,Int,Int)) -> Int -> (Int,Int,Int) -> Int
+ #-}
+
+lessSafeIndex :: Ix i => (i, i) -> Int -> i -> Int
+-- See Note [Double bounds-checking of index values]
+-- Do only (A), the semantic check
+lessSafeIndex (l,u) _ i = index (l,u) i
+
+-- Don't inline this long error message everywhere!!
+badSafeIndex :: Int -> Int -> Int
+badSafeIndex i' n = error ("Error in array index; " ++ show i' ++
+ " not in range [0.." ++ show n ++ ")")
{-# INLINE unsafeAt #-}
unsafeAt :: Ix i => Array i e -> Int -> e
assocs arr@(Array l u _ _) =
[(i, arr ! i) | i <- range (l,u)]
--- | The 'accumArray' deals with repeated indices in the association
+-- | The 'accumArray' function deals with repeated indices in the association
-- list using an /accumulating function/ which combines the values of
-- associations with the same index.
-- For example, given a list of values of some index type, @hist@
{-# INLINE adjust #-}
adjust :: (e -> a -> e) -> MutableArray# s e -> (Int, a) -> STRep s b -> STRep s b
-adjust f marr# (I# i#, new) next s1# =
- case readArray# marr# i# s1# of
- (# s2#, old #) ->
- case writeArray# marr# i# (f old new) s2# of
- s3# -> next s3#
+-- See NB on 'fill'
+adjust f marr# (I# i#, new) next
+ = \s1# -> case readArray# marr# i# s1# of
+ (# s2#, old #) ->
+ case writeArray# marr# i# (f old new) s2# of
+ s3# -> next s3#
-- | Constructs an array identical to the first argument except that it has
-- been updated by the associations in the right argument.
projects / ghc-base.git / blobdiff