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217 lines
7.5 KiB
Idris
217 lines
7.5 KiB
Idris
--
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-- Specification
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--
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-- a. Unsigned integers
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--
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-- Unsigned integers with a precision of x bit have a valid
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-- range of [0,2^x - 1]. They support all the usual arithmetic
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-- operations: +,*,-,div, and mod. If the result y of an operation
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-- is outside the valid range, the unsigned remainder modulo 2^x of y
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-- is returned instead. The same kind of truncation happens when
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-- other numeric types are cast to one of the unsigned integer
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-- types.
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--
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-- Example: For `Bits8` the valid range is [0,255]. Below are some
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-- example calculations. All numbers are considered to be of type `Bits8`
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-- unless specified otherwise:
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--
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-- 255 + 7 = 6
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-- 3 * 128 = 128
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-- (-1) = 255
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-- 7 - 10 = 253
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--
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-- b. Signed integers
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--
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-- Signed integers with a precision of x bit have a valid
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-- range of [-2^(x-1),2^(x-1) - 1]. They support all the usual arithmetic
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-- operations: +,*,-,div, and mod. If the result `y` of an operation
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-- is outside the valid range, the signed remainder modulo 2^x of `y`
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-- is calculated and 2^x subtracted from the result if it
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-- is still out of bounds. The same kind of truncation happens when
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-- other numeric types are cast to one of the signed integer
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-- types.
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--
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-- Example: For `Int8` the valid range is [-128,127]. Below are some
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-- example calculations. All numbers are considered to be of type `Int8`
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-- unless specified otherwise:
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--
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-- 127 + 7 = -122
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-- 3 * 64 = -64
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-- 2 * (-64) = -128
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-- (-129) = 127
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-- 7 - 10 = -3
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--
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import Data.List
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import Data.Stream
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record IntType (a : Type) where
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constructor MkIntType
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name : String
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signed : Bool
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precision : Integer
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min : Integer
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max : Integer
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intType : Bool -> String -> Integer -> IntType a
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intType True n p = let ma = prim__shl_Integer 1 (p - 1)
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in MkIntType n True p (negate ma) (ma - 1)
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intType False n p = let ma = prim__shl_Integer 1 p
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in MkIntType n False p 0 (ma - 1)
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bits8 : IntType Bits8
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bits8 = intType False "Bits8" 8
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bits16 : IntType Bits16
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bits16 = intType False "Bits16" 16
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bits32 : IntType Bits32
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bits32 = intType False "Bits32" 32
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bits64 : IntType Bits64
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bits64 = intType False "Bits64" 64
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int8 : IntType Int8
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int8 = intType True "Int8" 8
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int16 : IntType Int16
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int16 = intType True "Int16" 16
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int32 : IntType Int32
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int32 = intType True "Int32" 32
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int64 : IntType Int64
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int64 = intType True "Int64" 64
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int : IntType Int
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int = intType True "Int" 32
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record Op a where
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constructor MkOp
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name : String
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op : a -> a -> a
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opInt : Integer -> Integer -> Integer
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allowZero : Bool
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type : IntType a
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add : Num a => IntType a -> Op a
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add = MkOp "+" (+) (+) True
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sub : Neg a => IntType a -> Op a
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sub = MkOp "-" (-) (-) True
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mul : Num a => IntType a -> Op a
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mul = MkOp "*" (*) (*) True
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div : Integral a => IntType a -> Op a
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div = MkOp "div" (div) (div) False
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mod : Integral a => IntType a -> Op a
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mod = MkOp "mod" (mod) (mod) False
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pairs : List (Integer,Integer)
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pairs = let powsOf2 = [1,2,4,8,128,256,32768,65536,2147483648,4294967296,9223372036854775808,18446744073709551616]
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naturals = powsOf2 ++ map (\x => x-1) powsOf2
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-- positive and negative versions of naturals
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ints = naturals ++ map negate naturals
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-- naturals paired with ints
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in [| (,) ints naturals |]
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-- This check does the following: For a given binary operation `op`,
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-- calculate the result of applying the operation to all passed pairs
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-- of integers in `pairs` and check, with the given bit size, if
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-- the result is out of bounds. If it is, calculate the result
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-- modulo 2^bits. This gives the reference result as an `Integer`.
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--
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-- Now perform the same operation with the same input but for
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-- the integer type we'd like to check and cast the result back
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-- to an `Integer`. Create a nice error message for every pair
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-- that fails (returns an empty list if all goes well).
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check : (Num a, Cast a Integer) => Op a -> List String
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check (MkOp name op opInt allowZero $ MkIntType type signed bits mi ma) =
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let ps = if allowZero then pairs
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else filter ((0 /=) . checkBounds . snd) pairs
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in mapMaybe failing ps
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where
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trueMod : Integer -> Integer -> Integer
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trueMod x y = let res = x `mod` y
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in if res < 0 then res + y else res
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checkBounds : Integer -> Integer
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checkBounds n = let r1 = trueMod n (ma + 1 - mi)
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in if r1 > ma
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then r1 - (ma + 1 - mi)
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else r1
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failing : (Integer,Integer) -> Maybe String
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failing (x,y) =
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let resInteger = opInt x y
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resMod = checkBounds $ opInt (checkBounds x) (checkBounds y)
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resA = cast {to = Integer} (op (fromInteger x) (fromInteger y))
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in if resA == resMod
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then Nothing
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else Just #"Error when calculating \#{show x} \#{name} \#{show y} for \#{type}: Expected \#{show resMod} but got \#{show resA} (unrounded: \#{show resInteger})"#
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--------------------------------------------------------------------------------
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-- Main
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--------------------------------------------------------------------------------
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main : IO ()
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main = do traverse_ putStrLn . check $ add int8
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traverse_ putStrLn . check $ sub int8
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traverse_ putStrLn . check $ mul int8
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traverse_ putStrLn . check $ div int8
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traverse_ putStrLn . check $ mod int8
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traverse_ putStrLn . check $ add int16
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traverse_ putStrLn . check $ sub int16
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traverse_ putStrLn . check $ mul int16
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traverse_ putStrLn . check $ div int16
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traverse_ putStrLn . check $ mod int16
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traverse_ putStrLn . check $ add int32
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traverse_ putStrLn . check $ sub int32
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traverse_ putStrLn . check $ mul int32
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traverse_ putStrLn . check $ div int32
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traverse_ putStrLn . check $ mod int32
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traverse_ putStrLn . check $ add int64
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traverse_ putStrLn . check $ sub int64
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traverse_ putStrLn . check $ mul int64
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traverse_ putStrLn . check $ div int64
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traverse_ putStrLn . check $ mod int64
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traverse_ putStrLn . check $ add int
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traverse_ putStrLn . check $ sub int
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traverse_ putStrLn . check $ mul int
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traverse_ putStrLn . check $ div int
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traverse_ putStrLn . check $ mod int
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traverse_ putStrLn . check $ add bits8
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traverse_ putStrLn . check $ sub bits8
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traverse_ putStrLn . check $ mul bits8
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traverse_ putStrLn . check $ div bits8
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traverse_ putStrLn . check $ mod bits8
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traverse_ putStrLn . check $ add bits16
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traverse_ putStrLn . check $ sub bits16
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traverse_ putStrLn . check $ mul bits16
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traverse_ putStrLn . check $ div bits16
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traverse_ putStrLn . check $ mod bits16
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traverse_ putStrLn . check $ add bits32
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traverse_ putStrLn . check $ sub bits32
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traverse_ putStrLn . check $ mul bits32
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traverse_ putStrLn . check $ div bits32
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traverse_ putStrLn . check $ mod bits32
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traverse_ putStrLn . check $ add bits64
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traverse_ putStrLn . check $ sub bits64
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traverse_ putStrLn . check $ mul bits64
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traverse_ putStrLn . check $ div bits64
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traverse_ putStrLn . check $ mod bits64
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