3 import Language.Haskell.Syntax
5 main = do show_add exp_adder; show_add rec_adder;
7 show_add f = do print ("Sum: " ++ (displaysigs s)); print ("Carry: " ++ (displaysig c))
9 a = [High, High, High, High]
10 b = [Low, Low, Low, High]
13 -- Not really an adder, but this is nice minimal hardware description
17 -- Not really an adder either, but a slightly more complex example
21 -- Combinatoric stateless no-carry adder
23 no_carry_adder :: (Bit, Bit) -> Bit
24 no_carry_adder (a, b) = a `hwxor` b
26 -- Combinatoric stateless half adder
28 half_adder :: (Bit, Bit) -> (Bit, Bit)
30 ( a `hwxor` b, a `hwand` b )
32 -- Combinatoric stateless full adder
33 -- (A, B, C) -> (S, C)
34 full_adder :: (Bit, Bit, Bit) -> (Bit, Bit)
35 full_adder (a, b, cin) = (s, c)
37 s = a `hwxor` b `hwxor` cin
38 c = a `hwand` b `hwor` (cin `hwand` (a `hwxor` b))
42 -- [a] -> [b] -> ([s], cout)
43 exp_adder :: ([Bit], [Bit]) -> ([Bit], Bit)
45 exp_adder ([a3,a2,a1,a0], [b3,b2,b1,b0]) =
46 ([s3, s2, s1, s0], c3)
48 (s0, c0) = full_adder (a0, b0, Low)
49 (s1, c1) = full_adder (a1, b1, c0)
50 (s2, c2) = full_adder (a2, b2, c1)
51 (s3, c3) = full_adder (a3, b3, c2)
53 -- Any number of bits adder
55 -- [a] -> [b] -> ([s], cout)
56 rec_adder :: ([Bit], [Bit]) -> ([Bit], Bit)
58 rec_adder ([], []) = ([], Low)
59 rec_adder ((a:as), (b:bs)) =
62 (rest, cin) = rec_adder (as, bs)
63 (s, cout) = full_adder (a, b, cin)
65 -- Four bit adder, using the continous adder below
66 -- [a] -> [b] -> ([s], cout)
68 -- ([s3, s2, s1, s0], c)
70 -- ((s0, _):(s1, _):(s2, _):(s3, c):_) = con_adder (zip ((reverse as) ++ lows) ((reverse bs) ++ lows))
72 -- Continuous sequential version
73 -- Stream a -> Stream b -> Stream (sum, cout)
74 --con_adder :: Stream (Bit, Bit) -> Stream (Bit, Bit)
76 -- Forward to con_adder_int, but supply an initial state
78 -- con_adder_int pin Low
80 -- Stream a -> Stream b -> state -> Stream (s, c)
81 --con_adder_int :: Stream (Bit, Bit) -> Bit -> Stream (Bit, Bit)
82 --con_adder_int ((a,b):rest) cin =
83 -- (s, cout) : con_adder_int rest cout
85 -- (s, cout) = full_adder a b cin
87 -- vim: set ts=8 sw=2 sts=2 expandtab: