-module Adders (main, no_carry_adder) where
+module Adders where
import Bits
+import qualified Sim
import Language.Haskell.Syntax
-main = do show_add exp_adder; show_add rec_adder;
+mainIO f = Sim.simulateIO (Sim.stateless f) ()
+
+-- This function is from Sim.hs, but we redefine it here so it can get inlined
+-- by default.
+stateless :: (i -> o) -> (i -> () -> ((), o))
+stateless f = \i s -> (s, f i)
show_add f = do print ("Sum: " ++ (displaysigs s)); print ("Carry: " ++ (displaysig c))
where
b = [Low, Low, Low, High]
(s, c) = f (a, b)
--- Combinatoric no-carry adder
+mux2 :: Bit -> (Bit, Bit) -> Bit
+mux2 Low (a, b) = a
+mux2 High (a, b) = b
+
+-- Not really an adder, but this is nice minimal hardware description
+wire :: Bit -> Bit
+wire a = a
+
+-- Not really an adder either, but a slightly more complex example
+inv :: Bit -> Bit
+inv a = hwnot a
+
+-- Not really an adder either, but a slightly more complex example
+invinv :: Bit -> Bit
+invinv a = hwnot (hwnot a)
+
+-- Not really an adder either, but a slightly more complex example
+dup :: Bit -> (Bit, Bit)
+dup a = (a, a)
+
+-- Not really an adder either, but a simple stateful example (D-flipflop)
+dff :: Bit -> Bit -> (Bit, Bit)
+dff d s = (s', q)
+ where
+ q = s
+ s' = d
+
+type ShifterState = (Bit, Bit, Bit, Bit)
+shifter :: Bit -> ShifterState -> (ShifterState, Bit)
+shifter a s =
+ (s', o)
+ where
+ s' = (a, b, c, d)
+ (b, c, d, o) = s
+
+-- Combinatoric stateless no-carry adder
-- A -> B -> S
no_carry_adder :: (Bit, Bit) -> Bit
no_carry_adder (a, b) = a `hwxor` b
--- Combinatoric (one-bit) full adder
+-- Combinatoric stateless half adder
+-- A -> B -> (S, C)
+half_adder :: (Bit, Bit) -> (Bit, Bit)
+{-# NOINLINE half_adder #-}
+half_adder (a, b) =
+ ( a `hwxor` b, a `hwand` b )
+
+-- Combinatoric stateless full adder
-- (A, B, C) -> (S, C)
full_adder :: (Bit, Bit, Bit) -> (Bit, Bit)
full_adder (a, b, cin) = (s, c)
where
- s = a `hwxor` b `hwxor` cin
- c = a `hwand` b `hwor` (cin `hwand` (a `hwxor` b))
+ (s1, c1) = half_adder(a, b)
+ (s, c2) = half_adder(s1, cin)
+ c = c1 `hwor` c2
+
+sfull_adder = stateless full_adder
-- Four bit adder
-- Explicit version