-- | 32-bit FNV-1a (Fowler-Noll-Vo) hash

{-# LANGUAGE CPP #-}
module Data.Generics.Fixplate.Util.Hash.FNV.FNV32 
  ( FNV32(..) 
  , unFNV32 
  ) 
  where

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import Data.Char
import Data.Word
import Data.Bits
-- import Data.Int
-- import Data.List

import Data.Generics.Fixplate.Util.Hash.Class 

--------------------------------------------------------------------------------

newtype FNV32 = FNV32 Word32 deriving (Eq,Ord,Show)

unFNV32 :: FNV32 -> Word32
unFNV32 (FNV32 x) = x

instance Hashable FNV32 where 
  hashDigest (FNV32 w) = hashDigest w

instance HashValue FNV32 where
  emptyHash = FNV32 fnv32_offset 
  hashHash (FNV32 w) = hashWord32 w
  showHex  (FNV32 w) = showHex32 w
  hashWord8  x (FNV32 w) = FNV32 (fnv32_octet  x w)
  hashWord16 x (FNV32 w) = FNV32 (fnv32_word16 x w)
  hashWord32 x (FNV32 w) = FNV32 (fnv32_word32 x w)
  hashWord64 x (FNV32 w) = FNV32 (fnv32_word64 x w)

--------------------------------------------------------------------------------

showHex32 :: Word32 -> String
showHex32 h = reverse $ worker 8 h where
  worker :: Int -> Word32 -> String
  worker 0 0 = []
  worker 0 _ = error "Hash/FNV32/showHex: shouldn't happen"
  worker i w = hexdigit (w .&. 15) : worker (i-1) (shiftR w 4) 
  hexdigit :: Word32 -> Char
  hexdigit n
    | k>=0 && k<=9   = chr (k+48)
    | otherwise      = chr (k+55)
    where k = fromIntegral n

--------------------------------------------------------------------------------
-- FNV-1a hash

fnv32_prime, fnv32_offset :: Word32

fnv32_prime  = 16777619   
fnv32_offset = 2166136261 

fnv32_octet :: Word8 -> Word32 -> Word32
fnv32_octet octet old = fnv32_prime * (old `xor` fromIntegral octet)

--------------------------------------------------------------------------------
-- 32 bit

fnv32_word32 :: Word32 -> Word32 -> Word32
fnv32_word32 w = fnv32_octet a . fnv32_octet b . fnv32_octet c . fnv32_octet d where
  a = fromIntegral (255 .&. (       w   ))
  b = fromIntegral (255 .&. (shiftR w  8))
  c = fromIntegral (255 .&. (shiftR w 16))
  d = fromIntegral (255 .&. (shiftR w 24))

{-
fnv32_word24 :: Word32 -> Word32 -> Word32
fnv32_word24 w = fnv32_octet a . fnv32_octet b . fnv32_octet c where
  a = fromIntegral (255 .&. (       w   ))
  b = fromIntegral (255 .&. (shiftR w  8))
  c = fromIntegral (255 .&. (shiftR w 16))
-}

fnv32_word16 :: Word16 -> Word32 -> Word32
fnv32_word16 w = fnv32_octet a . fnv32_octet b where
  a = fromIntegral (255 .&. (       w   ))
  b = fromIntegral (255 .&. (shiftR w  8))

fnv32_word64 :: Word64 -> Word32 -> Word32
fnv32_word64 w = fnv32_word32 a . fnv32_word32 b where
  a = fromIntegral (0xffffffff .&. (       w   ))
  b = fromIntegral (0xffffffff .&. (shiftR w 32))

--------------------------------------------------------------------------------