-- |
-- Module : Data.ASN1.Internal
-- License : BSD-style
-- Maintainer : Vincent Hanquez <vincent@snarc.org>
-- Stability : experimental
-- Portability : unknown
--
module Data.ASN1.Internal
( uintOfBytes
, intOfBytes
, bytesOfUInt
, bytesOfInt
, putVarEncodingIntegral
) where
import Data.Word
import Data.Bits
import Data.ByteString (ByteString)
import qualified Data.ByteString as B
{- | uintOfBytes returns the number of bytes and the unsigned integer represented by the bytes -}
uintOfBytes :: ByteString -> (Int, Integer)
uintOfBytes b = (B.length b, B.foldl (\acc n -> (acc `shiftL` 8) + fromIntegral n) 0 b)
--bytesOfUInt i = B.unfoldr (\x -> if x == 0 then Nothing else Just (fromIntegral (x .&. 0xff), x `shiftR` 8)) i
bytesOfUInt :: Integer -> [Word8]
bytesOfUInt x = reverse (list x)
where list i = if i <= 0xff then [fromIntegral i] else (fromIntegral i .&. 0xff) : list (i `shiftR` 8)
{- | intOfBytes returns the number of bytes in the list and
the represented integer by a two's completement list of bytes -}
intOfBytes :: ByteString -> (Int, Integer)
intOfBytes b
| B.length b == 0 = (0, 0)
| otherwise = (len, if isNeg then -(maxIntLen - v + 1) else v)
where
(len, v) = uintOfBytes b
maxIntLen = 2 ^ (8 * len) - 1
isNeg = testBit (B.head b) 7
{- | bytesOfInt convert an integer into a two's completemented list of bytes -}
bytesOfInt :: Integer -> [Word8]
bytesOfInt i
| i > 0 = if testBit (head uints) 7 then 0 : uints else uints
| i == 0 = [0]
| otherwise = if testBit (head nints) 7 then nints else 0xff : nints
where
uints = bytesOfUInt (abs i)
nints = reverse $ plusOne $ reverse $ map complement $ uints
plusOne [] = [1]
plusOne (x:xs) = if x == 0xff then 0 : plusOne xs else (x+1) : xs
{- ASN1 often uses a particular kind of 7-bit encoding of integers like
in the case of long tags or encoding of integer component of OID's.
Use this function for such an encoding. Assumes a positive integer.
Here is the description of the algorithm of the above encoding:
1. The integer is chunked up into 7-bit groups. Each of these 7bit
chunks are encoded as a single octet.
2. All the octets except the last one has its 8th bit set.
-}
putVarEncodingIntegral :: (Bits i, Integral i) => i -> ByteString
putVarEncodingIntegral i = B.reverse $ B.unfoldr genOctets (i,True)
where genOctets (x,first)
| x > 0 =
let out = fromIntegral (x .&. 0x7F) .|. (if first then 0 else 0x80) in
Just (out, (shiftR x 7, False))
| otherwise = Nothing