Data.Hash.Rolling

data-hash-0.2.0.1: Combinators for building fast hashing functions.

License | BSD-style
Maintainer | jcpetruzza@gmail.com
Stability | experimental
Portability | portable
Safe Haskell | None
Language | Haskell98

Data.Hash.Rolling

Contents

- The `RollingHash` type
  - Construction and manipulation
  - Querying

Description

Efficient implementation of a rolling hash, i.e., the computation of a hash through a moving window of a fixed size `n` over some stream. All operations are O(1) (in particular, they do not depend on the size of the window).

Some laws that this type satisfies:

-     currentHash rh == foldl1 combine (lastHashes rh)

-     length (lastHashes rh) <= windowSize rh

-     length (lastHashes $ addAndRoll rh a) == windowSize rh -- whenever length (lastHashes rh) == windowSize rh

-     last (lastHashes $ addAndRoll rh x) == hash a

-     init (lastHashes $ addAndRoll rh a) isSuffixOf (lastHashes rh)

Synopsis

- data RollingHash a
- rollingHash :: Int -> RollingHash a
- addAndRoll :: Hashable a => RollingHash a -> a -> RollingHash a
- currentHash :: RollingHash a -> Hash
- lastHashes :: RollingHash a -> [Hash]
- windowSize :: RollingHash a -> Int

# The `RollingHash` type

data RollingHash a

Instances

Show (RollingHash a) |

## Construction and manipulation

rollingHash :: Int -> RollingHash a

`rollingHash n` creates a `RollingHash` of window size `n` (for `n > 0`)

addAndRoll :: Hashable a => RollingHash a -> a -> RollingHash a

`addAndRoll x rh` adds a new input element and rolls the window one place through the input (if at least `n` elements were already consumed).

## Querying

currentHash :: RollingHash a -> Hash

lastHashes :: RollingHash a -> [Hash]

`lastHashes rh` returns the last `n` hashes.

windowSize :: RollingHash a -> Int