-- | Arrays of pointers to boxed values.
module Runtime.Prim.Array
export value
 allocArray     : [r1 r2 : Region]. Nat# -> Ptr# r1 Obj -> Ptr# r2 Obj
 writeArray     : [r1 r2 : Region]. Ptr# r1 Obj -> Nat# -> Ptr# r2 Obj -> Ptr# r1 Obj
 readArray      : [r1 r2 : Region]. Ptr# r1 Obj -> Nat# -> Ptr# r2 Obj
 fillArray      : [r1 r2 : Region]. Ptr# r1 Obj -> Nat# -> Nat# -> Ptr# r2 Obj -> Ptr# r1 Obj

import value
 allocBoxed     : [r1    : Region]. Tag# -> Nat# -> Ptr# r1 Obj
 setBoxed       : [r1 r2 : Region]. Ptr# r1 Obj  -> Nat# -> Ptr# r2 Obj -> Void#

with letrec


-- | Allocate an array of boxed values, consisting of the same element
--   for all positions.
allocArray 
        [r1 r2: Region]
        (len: Nat#) (val: Ptr# r1 Obj): Ptr# r2 Obj
 = do   arr     = allocBoxed [r2] (truncate# 0#) len
        fillArray arr 0# len val
        arr


-- | Write an element into an array.
writeArray 
        [r1 r2: Region] 
        (obj: Ptr# r1 Obj) (ix: Nat#) (val: Ptr# r2 Obj): Ptr# r1 Obj
 = do   
        -- Get address of the first byte after the end of the array.
        len     = promote# (peek# [r1] [Word32#] (castPtr# obj) 4#)
        top     = add# 8#  (shl# len (size2# [Addr#]))

        -- Bounded poke.
        -- If the requested address is past the end of the array then abort.
        off     = add# 8#  (shl# ix  (size2# [Addr#]))
        _       = pokeBounded# (castPtr# obj) off top val
        obj


-- | Read an element from an array.
readArray 
        [r1 r2: Region]
        (obj: Ptr# r1 Obj) (ix: Nat#): Ptr# r2 Obj
 = do   
        -- Get address of the first byte after the end of the array.
        len     = promote# (peek# [r1] [Word32#] (castPtr# obj) 4#) 
        top     = add# 8#  (shl#  len  (size2# [Addr#]))

        -- Bounded peek.
        -- If the requested address is past the end of the array then abort.
        off     = add# 8#  (shl#  ix   (size2# [Addr#]))
        result  = peekBounded# (castPtr# obj) off top
        result


-- | Fill all elements of an array with the same value.
fillArray
        [r1 r2: Region]
        (arr: Ptr# r1 Obj) (start end: Nat#) (val: Ptr# r2 Obj): Ptr# r1 Obj

 = case ge# start end of
        True#   -> arr
        False#  -> do
                setBoxed arr start val
                fillArray arr (add# start 1#) end val