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bundled/Crypto/Number/Serialize/Internal/LE.hs

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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