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module Hashable32 (Hash, Hashable (..), VisiHash (..), showHash, showsHash) where

import Data.List (foldl')

import Data.Word (Word32)

import Text.Printf

type Hash = Word32

showHash :: Hash -> String

showHash = printf "%#010x"

showsHash = showString . showHash

newtype VisiHash = VH Hash

instance Show VisiHash where

show (VH h) = showHash h

-- Combine two hash values. 0 is the left identity

combine :: Hash -> Hash -> Hash

combine a b = a * 16777619 + b

defaultSalt :: Hash

defaultSalt = 0xdeadbeef

class Hashable a where

hash :: a -> Hash

hash = hashWithSalt defaultSalt

hashWithSalt :: Hash -> a -> Hash

hashWithSalt s = combine s . hash

instance Hashable Word32 where

hash = id

instance Hashable Int where

hash = fromIntegral

instance Hashable Char where

hash = fromIntegral . fromEnum

instance (Hashable a, Hashable b) => Hashable (a, b) where

hash (a, b) = hash a `combine` hash b

instance Hashable a => Hashable [a] where

hash [] = 0

hash [x] = hash x

hash (x : xs) = hash x `combine` hash xs