77 lines
2.4 KiB
Haskell
77 lines
2.4 KiB
Haskell
-- |
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-- Module : Crypto.Number.Serialize.Internal
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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 using raw pointers
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{-# LANGUAGE BangPatterns #-}
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module Crypto.Number.Serialize.Internal
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( i2osp
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, i2ospOf
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, os2ip
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) where
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import Crypto.Number.Compat
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import Crypto.Number.Basic
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import Data.Bits
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import Data.Memory.PtrMethods
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import Data.Word (Word8)
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import Foreign.Ptr
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import Foreign.Storable
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-- | fill a pointer with the big endian binary representation of an integer
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--
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-- if the room available @ptrSz is less than the number of bytes needed,
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-- 0 is returned. Likewise if a parameter is invalid, 0 is returned.
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--
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-- returns the number of bytes written
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i2osp :: Integer -> Ptr Word8 -> Int -> IO Int
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i2osp m ptr ptrSz
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| ptrSz <= 0 = return 0
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| m < 0 = return 0
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| m == 0 = pokeByteOff ptr 0 (0 :: Word8) >> return 1
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| ptrSz < sz = return 0
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| otherwise = fillPtr ptr sz m >> return sz
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where
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!sz = numBytes m
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-- | Similar to 'i2osp', except it will pad any remaining space with zero.
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i2ospOf :: Integer -> Ptr Word8 -> Int -> IO Int
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i2ospOf m ptr ptrSz
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| ptrSz <= 0 = return 0
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| m < 0 = return 0
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| ptrSz < sz = return 0
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| otherwise = do
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memSet ptr 0 ptrSz
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fillPtr (ptr `plusPtr` padSz) sz m
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return ptrSz
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where
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!sz = numBytes m
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!padSz = ptrSz - sz
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fillPtr :: Ptr Word8 -> Int -> Integer -> IO ()
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fillPtr p sz m = gmpExportInteger m p `onGmpUnsupported` export (sz-1) m
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where
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export ofs i
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| ofs == 0 = pokeByteOff p ofs (fromIntegral i :: Word8)
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| otherwise = do
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let (i', b) = i `divMod` 256
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pokeByteOff p ofs (fromIntegral b :: Word8)
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export (ofs-1) i'
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-- | transform a big endian binary integer representation pointed by a pointer and a size
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-- into an integer
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os2ip :: Ptr Word8 -> Int -> IO Integer
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os2ip ptr ptrSz
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| ptrSz <= 0 = return 0
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| otherwise = gmpImportInteger ptrSz ptr `onGmpUnsupported` loop 0 0 ptr
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where
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loop :: Integer -> Int -> Ptr Word8 -> IO Integer
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loop !acc i p
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| i == ptrSz = return acc
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| otherwise = do
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w <- peekByteOff p i :: IO Word8
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loop ((acc `shiftL` 8) .|. fromIntegral w) (i+1) p
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