{-# OPTIONS_GHC -fno-implicit-prelude #-}
-----------------------------------------------------------------------------
-- |
-- Module : Data.HashTable
-- Copyright : (c) The University of Glasgow 2003
-- License : BSD-style (see the file libraries/base/LICENSE)
--
-- Maintainer : [email protected]
-- Stability : provisional
-- Portability : portable
--
-- An implementation of extensible hash tables, as described in
-- Per-Ake Larson, /Dynamic Hash Tables/, CACM 31(4), April 1988,
-- pp. 446--457. The implementation is also derived from the one
-- in GHC's runtime system (@ghc\/rts\/Hash.{c,h}@).
--
-----------------------------------------------------------------------------
module Data.HashTable (
-- * Basic hash table operations
HashTable, new, insert, delete, lookup, update,
-- * Converting to and from lists
fromList, toList,
-- * Hash functions
-- $hash_functions
hashInt, hashString,
prime,
-- * Diagnostics
longestChain
) where
-- This module is imported by Data.Dynamic, which is pretty low down in the
-- module hierarchy, so don't import "high-level" modules
#ifdef __GLASGOW_HASKELL__
import GHC.Base
#else
import Prelude hiding ( lookup )
#endif
import Data.Tuple ( fst )
import Data.Bits
import Data.Maybe
import Data.List ( maximumBy, length, concat, foldl', partition )
import Data.Int ( Int32 )
#if defined(__GLASGOW_HASKELL__)
import GHC.Num
import GHC.Real ( fromIntegral )
import GHC.Show ( Show(..) )
import GHC.Int ( Int64 )
import GHC.IOBase ( IO, IOArray, newIOArray,
unsafeReadIOArray, unsafeWriteIOArray, unsafePerformIO,
IORef, newIORef, readIORef, writeIORef )
#else
import Data.Char ( ord )
import Data.IORef ( IORef, newIORef, readIORef, writeIORef )
import System.IO.Unsafe ( unsafePerformIO )
import Data.Int ( Int64 )
# if defined(__HUGS__)
import Hugs.IOArray ( IOArray, newIOArray,
unsafeReadIOArray, unsafeWriteIOArray )
# elif defined(__NHC__)
import NHC.IOExtras ( IOArray, newIOArray, readIOArray, writeIOArray )
# endif
#endif
import Control.Monad ( mapM, mapM_, sequence_ )
-----------------------------------------------------------------------
iNSTRUMENTED :: Bool
iNSTRUMENTED = False
-----------------------------------------------------------------------
readHTArray :: HTArray a -> Int32 -> IO a
writeMutArray :: MutArray a -> Int32 -> a -> IO ()
freezeArray :: MutArray a -> IO (HTArray a)
thawArray :: HTArray a -> IO (MutArray a)
newMutArray :: (Int32, Int32) -> a -> IO (MutArray a)
#if defined(DEBUG) || defined(__NHC__)
type MutArray a = IOArray Int32 a
type HTArray a = MutArray a
newMutArray = newIOArray
readHTArray = readIOArray
writeMutArray = writeIOArray
freezeArray = return
thawArray = return
#else
type MutArray a = IOArray Int32 a
type HTArray a = MutArray a -- Array Int32 a
newMutArray = newIOArray
readHTArray arr i = readMutArray arr i -- return $! (unsafeAt arr (fromIntegral i))
readMutArray :: MutArray a -> Int32 -> IO a
readMutArray arr i = unsafeReadIOArray arr (fromIntegral i)
writeMutArray arr i x = unsafeWriteIOArray arr (fromIntegral i) x
freezeArray = return -- unsafeFreeze
thawArray = return -- unsafeThaw
#endif
data HashTable key val = HashTable {
cmp :: !(key -> key -> Bool),
hash_fn :: !(key -> Int32),
tab :: !(IORef (HT key val))
}
-- TODO: the IORef should really be an MVar.
data HT key val
= HT {
kcount :: !Int32, -- Total number of keys.
bmask :: !Int32,
buckets :: !(HTArray [(key,val)])
}
-- ------------------------------------------------------------
-- Instrumentation for performance tuning
-- This ought to be roundly ignored after optimization when
-- iNSTRUMENTED=False.
-- STRICT version of modifyIORef!
modifyIORef :: IORef a -> (a -> a) -> IO ()
modifyIORef r f = do
v <- readIORef r
let z = f v in z `seq` writeIORef r z
data HashData = HD {
tables :: !Integer,
insertions :: !Integer,
lookups :: !Integer,
totBuckets :: !Integer,
maxEntries :: !Int32,
maxChain :: !Int,
maxBuckets :: !Int32
} deriving (Eq, Show)
{-# NOINLINE hashData #-}
hashData :: IORef HashData
hashData = unsafePerformIO (newIORef (HD { tables=0, insertions=0, lookups=0,
totBuckets=0, maxEntries=0,
maxChain=0, maxBuckets=tABLE_MIN } ))
instrument :: (HashData -> HashData) -> IO ()
instrument i | iNSTRUMENTED = modifyIORef hashData i
| otherwise = return ()
recordNew :: IO ()
recordNew = instrument rec
where rec hd@HD{ tables=t, totBuckets=b } =
hd{ tables=t+1, totBuckets=b+fromIntegral tABLE_MIN }
recordIns :: Int32 -> Int32 -> [a] -> IO ()
recordIns i sz bkt = instrument rec
where rec hd@HD{ insertions=ins, maxEntries=mx, maxChain=mc } =
hd{ insertions=ins+fromIntegral i, maxEntries=mx `max` sz,
maxChain=mc `max` length bkt }
recordResize :: Int32 -> Int32 -> IO ()
recordResize older newer = instrument rec
where rec hd@HD{ totBuckets=b, maxBuckets=mx } =
hd{ totBuckets=b+fromIntegral (newer-older),
maxBuckets=mx `max` newer }
recordLookup :: IO ()
recordLookup = instrument lkup
where lkup hd@HD{ lookups=l } = hd{ lookups=l+1 }
-- stats :: IO String
-- stats = fmap show $ readIORef hashData
-- -----------------------------------------------------------------------------
-- Sample hash functions
-- $hash_functions
--
-- This implementation of hash tables uses the low-order /n/ bits of the hash
-- value for a key, where /n/ varies as the hash table grows. A good hash
-- function therefore will give an even distribution regardless of /n/.
--
-- If your keyspace is integrals such that the low-order bits between
-- keys are highly variable, then you could get away with using 'id'
-- as the hash function.
--
-- We provide some sample hash functions for 'Int' and 'String' below.
golden :: Int32
golden = -1640531527
-- | A sample (and useful) hash function for Int and Int32,
-- implemented by extracting the uppermost 32 bits of the 64-bit
-- result of multiplying by a 32-bit constant. The constant is from
-- Knuth, derived from the golden ratio:
--
-- > golden = round ((sqrt 5 - 1) * 2^31) :: Int
hashInt :: Int -> Int32
hashInt x = mulHi (fromIntegral x) golden
-- hi 32 bits of a x-bit * 32 bit -> 64-bit multiply
mulHi :: Int32 -> Int32 -> Int32
mulHi a b = fromIntegral (r `shiftR` 32)
where r :: Int64
r = fromIntegral a * fromIntegral b :: Int64
-- | A sample hash function for Strings. We keep multiplying by the
-- golden ratio and adding. The implementation is:
--
-- > hashString = foldl' f 0
-- > where f m c = fromIntegral (fromEnum c + 1) * golden + mulHi m golden
--
-- Note that this has not been extensively tested for reasonability,
-- but Knuth argues that repeated multiplication by the golden ratio
-- will minimize gaps in the hash space.
hashString :: String -> Int32
hashString = foldl' f 0
where f m c = fromIntegral (ord c + 1) * golden + mulHi m golden
-- | A prime larger than the maximum hash table size
prime :: Int32
prime = 33554467
-- -----------------------------------------------------------------------------
-- Parameters
tABLE_MAX :: Int32
tABLE_MAX = 32 * 1024 * 1024 -- Maximum size of hash table
tABLE_MIN :: Int32
tABLE_MIN = 8
hLOAD :: Int32
hLOAD = 7 -- Maximum average load of a single hash bucket
hYSTERESIS :: Int32
hYSTERESIS = 64 -- entries to ignore in load computation
{- Hysteresis favors long association-list-like behavior for small tables. -}
-- -----------------------------------------------------------------------------
-- Creating a new hash table
-- | Creates a new hash table. The following property should hold for the @eq@
-- and @hash@ functions passed to 'new':
--
-- > eq A B => hash A == hash B
--
new
:: (key -> key -> Bool) -- ^ @eq@: An equality comparison on keys
-> (key -> Int32) -- ^ @hash@: A hash function on keys
-> IO (HashTable key val) -- ^ Returns: an empty hash table
new cmpr hash = do
recordNew
-- make a new hash table with a single, empty, segment
let mask = tABLE_MIN-1
bkts' <- newMutArray (0,mask) []
bkts <- freezeArray bkts'
let
kcnt = 0
ht = HT { buckets=bkts, kcount=kcnt, bmask=mask }
table <- newIORef ht
return (HashTable { tab=table, hash_fn=hash, cmp=cmpr })
-- -----------------------------------------------------------------------------
-- Inserting a key\/value pair into the hash table
-- | Inserts a key\/value mapping into the hash table.
--
-- Note that 'insert' doesn't remove the old entry from the table -
-- the behaviour is like an association list, where 'lookup' returns
-- the most-recently-inserted mapping for a key in the table. The
-- reason for this is to keep 'insert' as efficient as possible. If
-- you need to update a mapping, then we provide 'update'.
--
insert :: HashTable key val -> key -> val -> IO ()
insert ht key val =
updatingBucket CanInsert (\bucket -> ((key,val):bucket, 1, ())) ht key
-- ------------------------------------------------------------
-- The core of the implementation is lurking down here, in findBucket,
-- updatingBucket, and expandHashTable.
tooBig :: Int32 -> Int32 -> Bool
tooBig k b = k-hYSTERESIS > hLOAD * b
-- index of bucket within table.
bucketIndex :: Int32 -> Int32 -> Int32
bucketIndex mask h = h .&. mask
-- find the bucket in which the key belongs.
-- returns (key equality, bucket index, bucket)
--
-- This rather grab-bag approach gives enough power to do pretty much
-- any bucket-finding thing you might want to do. We rely on inlining
-- to throw away the stuff we don't want. I'm proud to say that this
-- plus updatingBucket below reduce most of the other definitions to a
-- few lines of code, while actually speeding up the hashtable
-- implementation when compared with a version which does everything
-- from scratch.
{-# INLINE findBucket #-}
findBucket :: HashTable key val -> key -> IO (HT key val, Int32, [(key,val)])
findBucket HashTable{ tab=ref, hash_fn=hash} key = do
table@HT{ buckets=bkts, bmask=b } <- readIORef ref
let indx = bucketIndex b (hash key)
bucket <- readHTArray bkts indx
return (table, indx, bucket)
data Inserts = CanInsert
| Can'tInsert
deriving (Eq)
-- updatingBucket is the real workhorse of all single-element table
-- updates. It takes a hashtable and a key, along with a function
-- describing what to do with the bucket in which that key belongs. A
-- flag indicates whether this function may perform table insertions.
-- The function returns the new contents of the bucket, the number of
-- bucket entries inserted (negative if entries were deleted), and a
-- value which becomes the return value for the function as a whole.
-- The table sizing is enforced here, calling out to expandSubTable as
-- necessary.
-- This function is intended to be inlined and specialized for every
-- calling context (eg every provided bucketFn).
{-# INLINE updatingBucket #-}
updatingBucket :: Inserts -> ([(key,val)] -> ([(key,val)], Int32, a)) ->
HashTable key val -> key ->
IO a
updatingBucket canEnlarge bucketFn
ht@HashTable{ tab=ref, hash_fn=hash } key = do
(table@HT{ kcount=k, buckets=bkts, bmask=b },
indx, bckt) <- findBucket ht key
(bckt', inserts, result) <- return $ bucketFn bckt
let k' = k + inserts
table1 = table { kcount=k' }
bkts' <- thawArray bkts
writeMutArray bkts' indx bckt'
freezeArray bkts'
table2 <- if canEnlarge == CanInsert && inserts > 0 then do
recordIns inserts k' bckt'
if tooBig k' b
then expandHashTable hash table1
else return table1
else return table1
writeIORef ref table2
return result
expandHashTable :: (key -> Int32) -> HT key val -> IO (HT key val)
expandHashTable hash table@HT{ buckets=bkts, bmask=mask } = do
let
oldsize = mask + 1
newmask = mask + mask + 1
recordResize oldsize (newmask+1)
--
if newmask > tABLE_MAX-1
then return table
else do
--
newbkts' <- newMutArray (0,newmask) []
let
splitBucket oldindex = do
bucket <- readHTArray bkts oldindex
let (oldb,newb) =
partition ((oldindex==). bucketIndex newmask . hash . fst) bucket
writeMutArray newbkts' oldindex oldb
writeMutArray newbkts' (oldindex + oldsize) newb
mapM_ splitBucket [0..mask]
newbkts <- freezeArray newbkts'
return ( table{ buckets=newbkts, bmask=newmask } )
-- -----------------------------------------------------------------------------
-- Deleting a mapping from the hash table
-- Remove a key from a bucket
deleteBucket :: (key -> Bool) -> [(key,val)] -> ([(key, val)], Int32, ())
deleteBucket _ [] = ([],0,())
deleteBucket del (pair@(k,_):bucket) =
case deleteBucket del bucket of
(bucket', dels, _) | del k -> dels' `seq` (bucket', dels', ())
| otherwise -> (pair:bucket', dels, ())
where dels' = dels - 1
-- | Remove an entry from the hash table.
delete :: HashTable key val -> key -> IO ()
delete ht@HashTable{ cmp=eq } key =
updatingBucket Can'tInsert (deleteBucket (eq key)) ht key
-- -----------------------------------------------------------------------------
-- Updating a mapping in the hash table
-- | Updates an entry in the hash table, returning 'True' if there was
-- already an entry for this key, or 'False' otherwise. After 'update'
-- there will always be exactly one entry for the given key in the table.
--
-- 'insert' is more efficient than 'update' if you don't care about
-- multiple entries, or you know for sure that multiple entries can't
-- occur. However, 'update' is more efficient than 'delete' followed
-- by 'insert'.
update :: HashTable key val -> key -> val -> IO Bool
update ht@HashTable{ cmp=eq } key val =
updatingBucket CanInsert
(\bucket -> let (bucket', dels, _) = deleteBucket (eq key) bucket
in ((key,val):bucket', 1+dels, dels/=0))
ht key
-- -----------------------------------------------------------------------------
-- Looking up an entry in the hash table
-- | Looks up the value of a key in the hash table.
lookup :: HashTable key val -> key -> IO (Maybe val)
lookup ht@HashTable{ cmp=eq } key = do
recordLookup
(_, _, bucket) <- findBucket ht key
let firstHit (k,v) r | eq key k = Just v
| otherwise = r
return (foldr firstHit Nothing bucket)
-- -----------------------------------------------------------------------------
-- Converting to/from lists
-- | Convert a list of key\/value pairs into a hash table. Equality on keys
-- is taken from the Eq instance for the key type.
--
fromList :: (Eq key) => (key -> Int32) -> [(key,val)] -> IO (HashTable key val)
fromList hash list = do
table <- new (==) hash
sequence_ [ insert table k v | (k,v) <- list ]
return table
-- | Converts a hash table to a list of key\/value pairs.
--
toList :: HashTable key val -> IO [(key,val)]
toList = mapReduce id concat
{-# INLINE mapReduce #-}
mapReduce :: ([(key,val)] -> r) -> ([r] -> r) -> HashTable key val -> IO r
mapReduce m r HashTable{ tab=ref } = do
HT{ buckets=bckts, bmask=b } <- readIORef ref
fmap r (mapM (fmap m . readHTArray bckts) [0..b])
-- -----------------------------------------------------------------------------
-- Diagnostics
-- | This function is useful for determining whether your hash
-- function is working well for your data set. It returns the longest
-- chain of key\/value pairs in the hash table for which all the keys
-- hash to the same bucket. If this chain is particularly long (say,
-- longer than 14 elements or so), then it might be a good idea to try
-- a different hash function.
--
longestChain :: HashTable key val -> IO [(key,val)]
longestChain = mapReduce id (maximumBy lengthCmp)
where lengthCmp (_:x)(_:y) = lengthCmp x y
lengthCmp [] [] = EQ
lengthCmp [] _ = LT
lengthCmp _ [] = GT
|
