Hashable32.hs

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