Hash

module Hash exposing (hash)

{-| A simple hash function for Elm.

@docs hash
-}

import Bitwise exposing (shiftLeft)
import Char exposing (toCode)
import String exposing (foldl)


{-
from http://www.cse.yorku.ca/~oz/hash.html

```c
unsigned long hash(unsigned char *str) {
  unsigned long hash = 5381;
  int c;

  while (c = *str++)
    hash = ((hash << 5) + hash) + c; /* hash * 33 + c */

  return hash;
}
```
-}

{-|
Hashes a String to an Int using the
[djb2](http://www.cse.yorku.ca/~oz/hash.html) algorithm. This is in no way
cryptographically secure. It is just for turning abirary strings in to numbers.

    hash "yolo swaggins" == 2438413579
-}
hash : String -> Int
hash str =
  foldl updateHash 5381 str


updateHash : Char -> Int -> Int
updateHash c h =
  (h `shiftLeft` 5) + h + toCode c