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Commit f687e48

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Improve some Int{Map,Set} bitwise ops (#1126)
* mask: Now creates the Prefix, skipping some unnecessary operations * branchMask: Shift the high bit right instead of the low bit left * branchPrefix: New function to directly create a Prefix instead of going via mask. The performance improvements appear to be too small to show up in benchmarks, but these changes also make the code nicer.
1 parent f602764 commit f687e48

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3 files changed

+31
-34
lines changed

3 files changed

+31
-34
lines changed

‎containers/src/Data/IntMap/Internal.hs

Lines changed: 7 additions & 13 deletions
Original file line numberDiff line numberDiff line change
@@ -286,7 +286,6 @@ module Data.IntMap.Internal (
286286
-- * Utility
287287
, link
288288
, linkKey
289-
, linkWithMask
290289
, bin
291290
, binCheckLeft
292291
, binCheckRight
@@ -330,6 +329,7 @@ import Data.IntSet.Internal.IntTreeCommons
330329
, signBranch
331330
, mask
332331
, branchMask
332+
, branchPrefix
333333
, TreeTreeBranch(..)
334334
, treeTreeBranch
335335
, i2w
@@ -2180,8 +2180,7 @@ mergeA
21802180
| i2w k1 < i2w k2 = binA p t1 t2
21812181
| otherwise = binA p t2 t1
21822182
where
2183-
m = branchMask k1 k2
2184-
p = Prefix (mask k1 m .|. m)
2183+
p = branchPrefix k1 k2
21852184
{-# INLINE linkA #-}
21862185

21872186
-- A variant of 'bin' that ensures that effects for negative keys are executed
@@ -3461,7 +3460,7 @@ ascLinkTop :: Stack a -> Int -> IntMap a -> Int -> Stack a
34613460
ascLinkTop stk !rk r !rm = case stk of
34623461
Nada -> Push rm r stk
34633462
Push m l stk'
3464-
| i2w m < i2w rm -> let p = Prefix (mask rk m.|. m)
3463+
| i2w m < i2w rm -> let p = mask rk m
34653464
in ascLinkTop stk' rk (Bin p l r) rm
34663465
| otherwise -> Push rm r stk
34673466

@@ -3478,7 +3477,7 @@ ascLinkStack stk !rk r = case stk of
34783477
| signBranch p -> Bin p r l
34793478
| otherwise -> ascLinkStack stk' rk (Bin p l r)
34803479
where
3481-
p = Prefix (mask rk m.|. m)
3480+
p = mask rk m
34823481

34833482
{--------------------------------------------------------------------
34843483
Eq
@@ -3652,17 +3651,12 @@ linkKey k1 t1 p2 t2 = link k1 t1 (unPrefix p2) t2
36523651
-- maps must be different. @k1@ must share the prefix of @t1@ and @k2@ must
36533652
-- share the prefix of @t2@.
36543653
link :: Int -> IntMap a -> Int -> IntMap a -> IntMap a
3655-
link k1 t1 k2 t2 = linkWithMask (branchMask k1 k2) k1 t1 k2 t2
3656-
{-# INLINE link #-}
3657-
3658-
-- `linkWithMask` is useful when the `branchMask` has already been computed
3659-
linkWithMask :: Int -> Key -> IntMap a -> Key -> IntMap a -> IntMap a
3660-
linkWithMask m k1 t1 k2 t2
3654+
link k1 t1 k2 t2
36613655
| i2w k1 < i2w k2 = Bin p t1 t2
36623656
| otherwise = Bin p t2 t1
36633657
where
3664-
p = Prefix (mask k1 m .|. m)
3665-
{-# INLINE linkWithMask #-}
3658+
p = branchPrefix k1 k2
3659+
{-# INLINE link #-}
36663660

36673661
{--------------------------------------------------------------------
36683662
@bin@ assures that we never have empty trees within a tree.

‎containers/src/Data/IntSet/Internal.hs

Lines changed: 7 additions & 12 deletions
Original file line numberDiff line numberDiff line change
@@ -207,6 +207,7 @@ import Data.IntSet.Internal.IntTreeCommons
207207
, signBranch
208208
, mask
209209
, branchMask
210+
, branchPrefix
210211
, TreeTreeBranch(..)
211212
, treeTreeBranch
212213
, i2w
@@ -1355,8 +1356,7 @@ fromRange (lx,rx)
13551356
| lx > rx = empty
13561357
| lp == rp = Tip lp (bitmapOf rx `shiftLL` 1 - bitmapOf lx)
13571358
| otherwise =
1358-
let m = branchMask lx rx
1359-
p = Prefix (mask lx m .|. m)
1359+
let p = branchPrefix lx rx
13601360
in if signBranch p -- handle negative numbers
13611361
then Bin p (goR 0) (goL 0)
13621362
else Bin p (goL (unPrefix p)) (goR (unPrefix p))
@@ -1444,7 +1444,7 @@ ascLinkTop :: Stack -> Int -> IntSet -> Int -> Stack
14441444
ascLinkTop stk !rk r !rm = case stk of
14451445
Nada -> Push rm r stk
14461446
Push m l stk'
1447-
| i2w m < i2w rm -> let p = Prefix (mask rk m.|. m)
1447+
| i2w m < i2w rm -> let p = mask rk m
14481448
in ascLinkTop stk' rk (Bin p l r) rm
14491449
| otherwise -> Push rm r stk
14501450

@@ -1461,7 +1461,7 @@ ascLinkStack stk !rk r = case stk of
14611461
| signBranch p -> Bin p r l
14621462
| otherwise -> ascLinkStack stk' rk (Bin p l r)
14631463
where
1464-
p = Prefix (mask rk m.|. m)
1464+
p = mask rk m
14651465

14661466
{--------------------------------------------------------------------
14671467
Eq
@@ -1698,17 +1698,12 @@ linkKey k1 t1 p2 t2 = link k1 t1 (unPrefix p2) t2
16981698
-- sets must be different. @k1@ must share the prefix of @t1@ and @k2@ must
16991699
-- share the prefix of @t2@.
17001700
link :: Int -> IntSet -> Int -> IntSet -> IntSet
1701-
link k1 t1 k2 t2 = linkWithMask (branchMask k1 k2) k1 t1 k2 t2
1702-
{-# INLINE link #-}
1703-
1704-
-- `linkWithMask` is useful when the `branchMask` has already been computed
1705-
linkWithMask :: Int -> Key -> IntSet -> Key -> IntSet -> IntSet
1706-
linkWithMask m k1 t1 k2 t2
1701+
link k1 t1 k2 t2
17071702
| i2w k1 < i2w k2 = Bin p t1 t2
17081703
| otherwise = Bin p t2 t1
17091704
where
1710-
p = Prefix (mask k1 m .|. m)
1711-
{-# INLINE linkWithMask #-}
1705+
p = branchPrefix k1 k2
1706+
{-# INLINE link #-}
17121707

17131708
{--------------------------------------------------------------------
17141709
@bin@ assures that we never have empty trees within a tree.

‎containers/src/Data/IntSet/Internal/IntTreeCommons.hs

Lines changed: 17 additions & 9 deletions
Original file line numberDiff line numberDiff line change
@@ -35,12 +35,13 @@ module Data.IntSet.Internal.IntTreeCommons
3535
, treeTreeBranch
3636
, mask
3737
, branchMask
38+
, branchPrefix
3839
, i2w
3940
, Order(..)
4041
) where
4142

4243
import Data.Bits (Bits(..), countLeadingZeros)
43-
import Utils.Containers.Internal.BitUtil (wordSize)
44+
import Utils.Containers.Internal.BitUtil (iShiftRL)
4445

4546
#ifdef __GLASGOW_HASKELL__
4647
import Language.Haskell.TH.Syntax (Lift)
@@ -144,20 +145,27 @@ signBranch :: Prefix -> Bool
144145
signBranch p = unPrefix p == (minBound :: Int)
145146
{-# INLINE signBranch #-}
146147

147-
-- | The prefix of key @i@ up to (but not including) the switching
148-
-- bit @m@.
149-
mask :: Key -> Int -> Int
150-
mask i m = i .&. ((-m) `xor` m)
148+
-- | The prefix of @Int@ @i@ up to the switching bit @m@.
149+
mask :: Int -> Int -> Prefix
150+
mask i m = Prefix ((i .&. negate m) .|. m)
151151
{-# INLINE mask #-}
152152

153-
-- | The first switching bit where the two prefixes disagree.
153+
-- | The first switching bit where the two @Int@s disagree.
154154
--
155-
-- Precondition for defined behavior: p1 /= p2
155+
-- Precondition for defined behavior: i1 /= i2
156156
branchMask :: Int -> Int -> Int
157-
branchMask p1 p2 =
158-
unsafeShiftL 1 (wordSize - 1 - countLeadingZeros (p1 `xor` p2))
157+
branchMask i1 i2 = iShiftRL (minBound :: Int) (countLeadingZeros (i1 `xor` i2))
159158
{-# INLINE branchMask #-}
160159

160+
-- | The shared prefix of two @Int@s.
161+
--
162+
-- Precondition for defined behavior: i1 /= i2
163+
branchPrefix :: Int -> Int -> Prefix
164+
branchPrefix i1 i2 = Prefix ((i1 .|. i2) .&. m)
165+
where
166+
m = unsafeShiftR (minBound :: Int) (countLeadingZeros (i1 `xor` i2))
167+
{-# INLINE branchPrefix #-}
168+
161169
i2w :: Int -> Word
162170
i2w = fromIntegral
163171
{-# INLINE i2w #-}

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