{- | Module : Foreign.C.Structs.Utils Description : Create C structs from Haskell Copyright : (c) Simon Plakolb, 2020 License : MIT Maintainer : s.plakolb@gmail.com Stability : beta This module defined some utility functions for Storable instance declarations. -} module Foreign.C.Structs.Utils ( next, fmax, sizeof ) where import Foreign.Storable (Storable, peek, sizeOf, alignment) import Foreign.Marshal (alloca) import Foreign.Ptr (Ptr, plusPtr, alignPtr) -- | Due to alignment constraints the size of C structs is dependent on the order of fields and their respectible sizes. The function 'sizeof' can calculate the resulting size given a list of all 'alignments' and 'sizes'. sizeof :: [Int] -> [Int] -> Int sizeof as@(_:alignments) (s:sizes) = sizeof' s alignments sizes where sizeof' s [] [] = s `pad` fmax as sizeof' x (a:as) (s:ss) = let s' = x+s in sizeof' (s' `pad` a) as ss pad x a | x `mod` a == 0 = x | otherwise = pad (x+1) a -- | Jumps to the next pointer location in the struct. next :: (Storable a, Storable b, Storable c) => Ptr a -> b -> IO (Ptr c) next ptr x = alloca \$ next' ptr x where next' :: (Storable a, Storable b, Storable c) => Ptr a -> b -> Ptr c -> IO (Ptr c) next' ptr x ptr_x = do let ptr_y = plusPtr ptr \$ sizeOf x y <- peek ptr_x return \$ alignPtr ptr_y \$ alignment y -- | Alias for @foldr max 0@. fmax :: Integral a => [a] -> a fmax = foldr max 0