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|
-- |
-- Module : Crypto.Number.Serialize.Internal.LE
-- License : BSD-style
-- Maintainer : Vincent Hanquez <vincent@snarc.org>
-- Stability : experimental
-- Portability : Good
--
-- Fast serialization primitives for integer using raw pointers (little endian)
{-# LANGUAGE BangPatterns #-}
module Crypto.Number.Serialize.Internal.LE
( i2osp
, i2ospOf
, os2ip
) where
import Crypto.Number.Compat
import Crypto.Number.Basic
import Data.Bits
import Data.Memory.PtrMethods
import Data.Word (Word8)
import Foreign.Ptr
import Foreign.Storable
-- | Fill a pointer with the little endian binary representation of an integer
--
-- If the room available @ptrSz@ is less than the number of bytes needed,
-- 0 is returned. Likewise if a parameter is invalid, 0 is returned.
--
-- Returns the number of bytes written
i2osp :: Integer -> Ptr Word8 -> Int -> IO Int
i2osp m ptr ptrSz
| ptrSz <= 0 = return 0
| m < 0 = return 0
| m == 0 = pokeByteOff ptr 0 (0 :: Word8) >> return 1
| ptrSz < sz = return 0
| otherwise = fillPtr ptr sz m >> return sz
where
!sz = numBytes m
-- | Similar to 'i2osp', except it will pad any remaining space with zero.
i2ospOf :: Integer -> Ptr Word8 -> Int -> IO Int
i2ospOf m ptr ptrSz
| ptrSz <= 0 = return 0
| m < 0 = return 0
| ptrSz < sz = return 0
| otherwise = do
memSet ptr 0 ptrSz
fillPtr ptr sz m
return ptrSz
where
!sz = numBytes m
fillPtr :: Ptr Word8 -> Int -> Integer -> IO ()
fillPtr p sz m = gmpExportIntegerLE m p `onGmpUnsupported` export 0 m
where
export ofs i
| ofs >= sz = return ()
| otherwise = do
let (i', b) = i `divMod` 256
pokeByteOff p ofs (fromIntegral b :: Word8)
export (ofs+1) i'
-- | Transform a little endian binary integer representation pointed by a
-- pointer and a size into an integer
os2ip :: Ptr Word8 -> Int -> IO Integer
os2ip ptr ptrSz
| ptrSz <= 0 = return 0
| otherwise = gmpImportIntegerLE ptrSz ptr `onGmpUnsupported` loop 0 (ptrSz-1) ptr
where
loop :: Integer -> Int -> Ptr Word8 -> IO Integer
loop !acc i !p
| i < 0 = return acc
| otherwise = do
w <- peekByteOff p i :: IO Word8
loop ((acc `shiftL` 8) .|. fromIntegral w) (i-1) p
|
