X-Git-Url: http://git.megacz.com/?a=blobdiff_plain;f=GHC%2FArr.lhs;h=1b2f0bb543da79b6bb50b1a0727593544732ba38;hb=2cf27b8981aec980350a291b90499916f1fbc8af;hp=a60e0b3f0fd47534232fd7cb7705513b247ac38d;hpb=4ef39162b8ae3ab239009e6386b5787475f172d9;p=ghc-base.git

diff --git a/GHC/Arr.lhs b/GHC/Arr.lhs
index a60e0b3..1b2f0bb 100644
--- a/GHC/Arr.lhs
+++ b/GHC/Arr.lhs
@@ -1,5 +1,6 @@
 \begin{code}
-{-# OPTIONS_GHC -fno-implicit-prelude -fno-bang-patterns -funbox-strict-fields #-}
+{-# OPTIONS_GHC -funbox-strict-fields #-}
+{-# LANGUAGE NoImplicitPrelude, NoBangPatterns #-}
 {-# OPTIONS_HADDOCK hide #-}
 -----------------------------------------------------------------------------
 -- |
@@ -32,9 +33,9 @@ default ()
 
 
 %*********************************************************
-%*							*
+%*                                                      *
 \subsection{The @Ix@ class}
-%*							*
+%*                                                      *
 %*********************************************************
 
 \begin{code}
@@ -60,52 +61,104 @@ default ()
 --
 class (Ord a) => Ix a where
     -- | The list of values in the subrange defined by a bounding pair.
-    range		:: (a,a) -> [a]
+    range               :: (a,a) -> [a]
     -- | The position of a subscript in the subrange.
-    index		:: (a,a) -> a -> Int
+    index               :: (a,a) -> a -> Int
     -- | Like 'index', but without checking that the value is in range.
-    unsafeIndex		:: (a,a) -> a -> Int
+    unsafeIndex         :: (a,a) -> a -> Int
     -- | Returns 'True' the given subscript lies in the range defined
     -- the bounding pair.
-    inRange		:: (a,a) -> a -> Bool
+    inRange             :: (a,a) -> a -> Bool
     -- | The size of the subrange defined by a bounding pair.
-    rangeSize		:: (a,a) -> Int
+    rangeSize           :: (a,a) -> Int
     -- | like 'rangeSize', but without checking that the upper bound is
     -- in range.
     unsafeRangeSize     :: (a,a) -> Int
 
-	-- Must specify one of index, unsafeIndex
-    index b i | inRange b i = unsafeIndex b i	
-	      | otherwise   = error "Error in array index"
+        -- 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   = hopelessIndexError
+
     unsafeIndex b i = index b i
 
     rangeSize b@(_l,h) | inRange b h = unsafeIndex b h + 1
-		       | otherwise   = 0	-- This case is only here to
-						-- check for an empty range
-	-- NB: replacing (inRange b h) by (l <= h) fails for
-	--     tuples.  E.g.  (1,2) <= (2,1) but the range is empty
+                       | otherwise   = 0        -- This case is only here to
+                                                -- check for an empty range
+        -- NB: replacing (inRange b h) by (l <= h) fails for
+        --     tuples.  E.g.  (1,2) <= (2,1) but the range is empty
 
     unsafeRangeSize b@(_l,h) = unsafeIndex b h + 1
 \end{code}
 
 Note that the following is NOT right
-	rangeSize (l,h) | l <= h    = index b h + 1
-			| otherwise = 0
+        rangeSize (l,h) | l <= h    = index b h + 1
+                        | otherwise = 0
 
 Because it might be the case that l<h, but the range
 is nevertheless empty.  Consider
-	((1,2),(2,1))
+        ((1,2),(2,1))
 Here l<h, but the second index ranges from 2..1 and
 hence is empty
 
 %*********************************************************
-%*							*
+%*                                                      *
 \subsection{Instances of @Ix@}
-%*							*
+%*                                                      *
 %*********************************************************
 
+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 #-}
@@ -113,8 +166,11 @@ indexError :: Show a => (a,a) -> a -> String -> b
 indexError rng i tp
   = error (showString "Ix{" . showString tp . showString "}.index: Index " .
            showParen True (showsPrec 0 i) .
-	   showString " out of range " $
-	   showParen True (showsPrec 0 rng) "")
+           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
@@ -124,23 +180,27 @@ instance  Ix Char  where
     {-# 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"
+              | otherwise   =  indexError b i "Char"
 
-    inRange (m,n) i	=  m <= i && i <= n
+    inRange (m,n) i     =  m <= i && i <= n
 
 ----------------------------------------------------------------------
 instance  Ix Int  where
     {-# INLINE range #-}
-	-- The INLINE stops the build in the RHS from getting inlined,
-	-- so that callers can fuse with the result of range
+        -- The INLINE stops the build in the RHS from getting inlined,
+        -- so that callers can fuse with the result of range
     range (m,n) = [m..n]
 
     {-# 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"
+              | otherwise   =  indexError b i "Int"
 
     {-# INLINE inRange #-}
     inRange (I# m,I# n) (I# i) =  m <=# i && i <=# n
@@ -153,10 +213,12 @@ instance  Ix Integer  where
     {-# 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"
+              | otherwise   =  indexError b i "Integer"
 
-    inRange (m,n) i	=  m <= i && i <= n
+    inRange (m,n) i     =  m <= i && i <= n
 
 ----------------------------------------------------------------------
 instance Ix Bool where -- as derived
@@ -166,8 +228,10 @@ instance Ix Bool where -- as derived
     {-# 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"
+              | otherwise   =  indexError b i "Bool"
 
     inRange (l,u) i = fromEnum i >= fromEnum l && fromEnum i <= fromEnum u
 
@@ -179,8 +243,10 @@ instance Ix Ordering where -- as derived
     {-# 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"
+              | otherwise   =  indexError b i "Ordering"
 
     inRange (l,u) i = fromEnum i >= fromEnum l && fromEnum i <= fromEnum u
 
@@ -192,7 +258,8 @@ instance Ix () where
     unsafeIndex   ((), ()) () = 0
     {-# INLINE inRange #-}
     inRange ((), ()) () = True
-    {-# INLINE index #-}
+
+    {-# INLINE index #-}  -- See Note [Inlining index]
     index b i = unsafeIndex b i
 
 ----------------------------------------------------------------------
@@ -277,9 +344,9 @@ instance  (Ix a1, Ix a2, Ix a3, Ix a4, Ix a5) => Ix (a1,a2,a3,a4,a5)  where
 \end{code}
 
 %*********************************************************
-%*							*
+%*                                                      *
 \subsection{The @Array@ types}
-%*							*
+%*                                                      *
 %*********************************************************
 
 \begin{code}
@@ -287,7 +354,6 @@ type IPr = (Int, Int)
 
 -- | 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
@@ -312,8 +378,8 @@ data STArray s i e
                                        -- used to make sure an index is
                                        -- really in range
                    (MutableArray# s e) -- The actual elements
-	-- No Ix context for STArray.  They are stupid,
-	-- and force an Ix context on the equality instance.
+        -- No Ix context for STArray.  They are stupid,
+        -- and force an Ix context on the equality instance.
 
 -- Just pointer equality on mutable arrays:
 instance Eq (STArray s i e) where
@@ -323,9 +389,9 @@ instance Eq (STArray s i e) where
 
 
 %*********************************************************
-%*							*
+%*                                                      *
 \subsection{Operations on immutable arrays}
-%*							*
+%*                                                      *
 %*********************************************************
 
 \begin{code}
@@ -360,18 +426,18 @@ arrEleBottom = error "(Array.!): undefined array element"
 -- with which the array was constructed.
 {-# INLINE array #-}
 array :: Ix i
-	=> (i,i)	-- ^ a pair of /bounds/, each of the index type
-			-- of the array.  These bounds are the lowest and
-			-- highest indices in the array, in that order.
-			-- For example, a one-origin vector of length
-			-- '10' has bounds '(1,10)', and a one-origin '10'
-			-- by '10' matrix has bounds '((1,1),(10,10))'.
-	-> [(i, e)]	-- ^ a list of /associations/ of the form
-			-- (/index/, /value/).  Typically, this list will
-			-- be expressed as a comprehension.  An
-			-- association '(i, x)' defines the value of
-			-- the array at index 'i' to be 'x'.
-	-> Array i e
+        => (i,i)        -- ^ a pair of /bounds/, each of the index type
+                        -- of the array.  These bounds are the lowest and
+                        -- highest indices in the array, in that order.
+                        -- For example, a one-origin vector of length
+                        -- '10' has bounds '(1,10)', and a one-origin '10'
+                        -- by '10' matrix has bounds '((1,1),(10,10))'.
+        -> [(i, e)]     -- ^ a list of /associations/ of the form
+                        -- (/index/, /value/).  Typically, this list will
+                        -- be expressed as a comprehension.  An
+                        -- association '(i, x)' defines the value of
+                        -- the array at index 'i' to be 'x'.
+        -> Array i e
 array (l,u) ies
     = let n = safeRangeSize (l,u)
       in unsafeArray' (l,u) n
@@ -429,15 +495,38 @@ arr@(Array l u n _) ! i = unsafeAt arr $ safeIndex (l,u) n i
 {-# 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' = unsafeIndex (l,u) i
+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"
+                         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
@@ -462,7 +551,7 @@ indices (Array l u _ _) = range (l,u)
 -- | The list of elements of an array in index order.
 {-# INLINE elems #-}
 elems :: Ix i => Array i e -> [e]
-elems arr@(Array l u n _) =
+elems arr@(Array _ _ n _) =
     [unsafeAt arr i | i <- [0 .. n - 1]]
 
 -- | The list of associations of an array in index order.
@@ -471,7 +560,7 @@ assocs :: Ix i => Array i e -> [(i, 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@
@@ -487,24 +576,24 @@ assocs arr@(Array l u _ _) =
 -- not in general be recursive.
 {-# INLINE accumArray #-}
 accumArray :: Ix i
-	=> (e -> a -> e)	-- ^ accumulating function
-	-> e			-- ^ initial value
-	-> (i,i)		-- ^ bounds of the array
-	-> [(i, a)]		-- ^ association list
-	-> Array i e
-accumArray f init (l,u) ies =
+        => (e -> a -> e)        -- ^ accumulating function
+        -> e                    -- ^ initial value
+        -> (i,i)                -- ^ bounds of the array
+        -> [(i, a)]             -- ^ association list
+        -> Array i e
+accumArray f initial (l,u) ies =
     let n = safeRangeSize (l,u)
-    in unsafeAccumArray' f init (l,u) n
+    in unsafeAccumArray' f initial (l,u) n
                          [(safeIndex (l,u) n i, e) | (i, e) <- ies]
 
 {-# INLINE unsafeAccumArray #-}
 unsafeAccumArray :: Ix i => (e -> a -> e) -> e -> (i,i) -> [(Int, a)] -> Array i e
-unsafeAccumArray f init b ies = unsafeAccumArray' f init b (rangeSize b) ies
+unsafeAccumArray f initial b ies = unsafeAccumArray' f initial b (rangeSize b) ies
 
 {-# INLINE unsafeAccumArray' #-}
 unsafeAccumArray' :: Ix i => (e -> a -> e) -> e -> (i,i) -> Int -> [(Int, a)] -> Array i e
-unsafeAccumArray' f init (l,u) n@(I# n#) ies = runST (ST $ \s1# ->
-    case newArray# n# init s1#          of { (# s2#, marr# #) ->
+unsafeAccumArray' f initial (l,u) n@(I# n#) ies = runST (ST $ \s1# ->
+    case newArray# n# initial s1#          of { (# s2#, marr# #) ->
     foldr (adjust f marr#) (done l u n marr#) ies s2# })
 
 {-# INLINE adjust #-}
@@ -600,9 +689,9 @@ cmpIntArray arr1@(Array l1 u1 n1 _) arr2@(Array l2 u2 n2 _) =
 
 
 %*********************************************************
-%*							*
+%*                                                      *
 \subsection{Array instances}
-%*							*
+%*                                                      *
 %*********************************************************
 
 \begin{code}
@@ -622,16 +711,16 @@ instance (Ix a, Show a, Show b) => Show (Array a b) where
         showsPrec appPrec1 (bounds a) .
         showChar ' ' .
         showsPrec appPrec1 (assocs a)
-	-- Precedence of 'array' is the precedence of application
+        -- Precedence of 'array' is the precedence of application
 
 -- The Read instance is in GHC.Read
 \end{code}
 
 
 %*********************************************************
-%*							*
+%*                                                      *
 \subsection{Operations on mutable arrays}
-%*							*
+%*                                                      *
 %*********************************************************
 
 Idle ADR question: What's the tradeoff here between flattening these
@@ -650,9 +739,9 @@ might be different, though.
 \begin{code}
 {-# INLINE newSTArray #-}
 newSTArray :: Ix i => (i,i) -> e -> ST s (STArray s i e)
-newSTArray (l,u) init = ST $ \s1# ->
+newSTArray (l,u) initial = ST $ \s1# ->
     case safeRangeSize (l,u)            of { n@(I# n#) ->
-    case newArray# n# init s1#          of { (# s2#, marr# #) ->
+    case newArray# n# initial s1#       of { (# s2#, marr# #) ->
     (# s2#, STArray l u n marr# #) }}
 
 {-# INLINE boundsSTArray #-}
@@ -687,9 +776,9 @@ unsafeWriteSTArray (STArray _ _ _ marr#) (I# i#) e = ST $ \s1# ->
 
 
 %*********************************************************
-%*							*
+%*                                                      *
 \subsection{Moving between mutable and immutable}
-%*							*
+%*                                                      *
 %*********************************************************
 
 \begin{code}