ez-couch-0.6.1: src/EZCouch/Base62.hs

{-# LANGUAGE DeriveDataTypeable #-}
{-# LANGUAGE OverloadedStrings #-}
{-# LANGUAGE NoMonomorphismRestriction #-}
module EZCouch.Base62 where

import Prelude ()
import ClassyPrelude
import qualified Data.List as List
import Data.Vector ((!))
import Data.Bits

chars = ['0'..'9'] ++ ['A'..'Z'] ++ ['a'..'z']
charsVector = asVector . fromList $ chars
charsLength = fromIntegral $ length charsVector

-- | Produces individual values for the whole range of ints including negatives. If you know that the value will allways be positive use `fromUnsigned64` instead.
fromSigned64 = fromUnsigned64 . zzEncode64 

fromUnsigned64 0 = charsVector ! 0 : []
fromUnsigned64 a = if a >= 0
  then reverse . fromUnsigned64' $ a
  else error $ "EZCouch.Base62.fromUnsigned64: Negative value: " ++ show a
  where
    fromUnsigned64' 0 = []
    fromUnsigned64' a = charsVector ! fromIntegral c : fromUnsigned64' b
      where
        b = div a charsLength 
        c = mod a charsLength

zzEncode64 :: Int64 -> Word64
zzEncode64 x = fromIntegral ((x `shiftL` 1) `xor` (x `shiftR` 63))