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bundled/Crypto/Internal/Builder.hs

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+-- |
+-- Module      : Crypto.Internal.Builder
+-- License     : BSD-style
+-- Maintainer  : Olivier Chéron <olivier.cheron@gmail.com>
+-- Stability   : stable
+-- Portability : Good
+--
+-- Delaying and merging ByteArray allocations.  This is similar to module
+-- "Data.ByteArray.Pack" except the total length is computed automatically based
+-- on what is appended.
+--
+{-# LANGUAGE BangPatterns #-}
+module Crypto.Internal.Builder
+    ( Builder
+    , buildAndFreeze
+    , builderLength
+    , byte
+    , bytes
+    , zero
+    ) where
+
+import           Data.ByteArray (ByteArray, ByteArrayAccess)
+import qualified Data.ByteArray as B
+import           Data.Memory.PtrMethods (memSet)
+
+import           Foreign.Ptr (Ptr, plusPtr)
+import           Foreign.Storable (poke)
+
+import           Crypto.Internal.Imports hiding (empty)
+
+data Builder =  Builder !Int (Ptr Word8 -> IO ())  -- size and initializer
+
+instance Semigroup Builder where
+    (Builder s1 f1) <> (Builder s2 f2) = Builder (s1 + s2) f
+      where f p = f1 p >> f2 (p `plusPtr` s1)
+
+builderLength :: Builder -> Int
+builderLength (Builder s _) = s
+
+buildAndFreeze :: ByteArray ba => Builder -> ba
+buildAndFreeze (Builder s f) = B.allocAndFreeze s f
+
+byte :: Word8 -> Builder
+byte !b = Builder 1 (`poke` b)
+
+bytes :: ByteArrayAccess ba => ba -> Builder
+bytes bs = Builder (B.length bs) (B.copyByteArrayToPtr bs)
+
+zero :: Int -> Builder
+zero s = if s > 0 then Builder s (\p -> memSet p 0 s) else empty
+
+empty :: Builder
+empty = Builder 0 (const $ return ())