66 lines
2.3 KiB
Haskell
66 lines
2.3 KiB
Haskell
-- |
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-- Module : Crypto.Number.Serialize
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-- License : BSD-style
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-- Maintainer : Vincent Hanquez <vincent@snarc.org>
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-- Stability : experimental
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-- Portability : Good
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--
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-- fast serialization primitives for integer
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{-# LANGUAGE BangPatterns #-}
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module Crypto.Number.Serialize
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( i2osp
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, os2ip
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, i2ospOf
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, i2ospOf_
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, lengthBytes
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) where
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import Data.Bits
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import Data.Word
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import Foreign.Storable
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import Crypto.Number.Compat
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import Crypto.Internal.Compat (unsafeDoIO)
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import qualified Crypto.Number.Serialize.Internal as Internal
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import qualified Crypto.Internal.ByteArray as B
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-- | os2ip converts a byte string into a positive integer
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os2ip :: B.ByteArrayAccess ba => ba -> Integer
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os2ip bs = unsafeDoIO $ B.withByteArray bs $ \src -> Internal.os2ip src (B.length bs)
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-- | i2osp converts a positive integer into a byte string
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--
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-- first byte is MSB (most significant byte), last byte is the LSB (least significant byte)
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i2osp :: B.ByteArray ba => Integer -> ba
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i2osp 0 = B.allocAndFreeze 1 $ \p -> pokeByteOff p 0 (0 :: Word8)
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i2osp m = B.allocAndFreeze sz (\p -> Internal.i2osp m p sz >> return ())
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where
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!sz = lengthBytes m
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-- | just like i2osp, but take an extra parameter for size.
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-- if the number is too big to fit in @len bytes, nothing is returned
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-- otherwise the number is padded with 0 to fit the @len required.
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i2ospOf :: B.ByteArray ba => Int -> Integer -> Maybe ba
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i2ospOf len m
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| len <= 0 = Nothing
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| m < 0 = Nothing
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| otherwise = Just $ B.unsafeCreate len $ \p -> Internal.i2ospOf m p len >> return ()
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--
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-- | just like i2ospOf except that it doesn't expect a failure: i.e.
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-- an integer larger than the number of output bytes requested
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--
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-- for example if you just took a modulo of the number that represent
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-- the size (example the RSA modulo n).
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i2ospOf_ :: B.ByteArray ba => Int -> Integer -> ba
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i2ospOf_ len = maybe (error "i2ospOf_: integer is larger than expected") id . i2ospOf len
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-- | returns the number of bytes to store an integer with i2osp
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--
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-- with integer-simple, this function is really slow.
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lengthBytes :: Integer -> Int
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lengthBytes n = gmpSizeInBytes n `onGmpUnsupported` nbBytes n
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where
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nbBytes !v
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| v < 256 = 1
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| otherwise = 1 + nbBytes (v `shiftR` 8)
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