NB. 8-bit adder and 8-bit ALU using 4 bit adders (circuit model)

require'circuits.ijs'

fourBitAdder =: monad define 
'a3 a2 a1 a0 b3 b2 b1 b0 cin' =. y.
t0 =. bitAdder a0 , b0 , cin
t1 =. bitAdder a1 , b1 , wireOutput 0 ; t0
t2 =. bitAdder a2 , b2 , wireOutput 0 ; t1
t3 =. bitAdder a3 , b3 , wireOutput 0 ; t2
(wireOutput 0 1 ; t3) , (wireOutput 1 ; t2) , (wireOutput 1 ; t1) , wireOutput 1 ; t0
)

NB. There are too many inputs in an 8-bit adder, so decimal inputs
NB. are used and converted, using the following utilities:

dtb =: (8#2)&#:
btd =: signed_value

NB. 8-bit adder

eightBitAdder =: monad define 
'a  b cin' =. dtb y.
t0 =. fourBitAdder (4 5 6 7 from a) , (4 5 6 7 from b) , 7 from cin
t1 =. fourBitAdder (0 1 2 3 from a) , (0 1 2 3 from b) , wireOutput 0 ; t0
btd (wireOutput 0 1 2 3 4 ; t1) , wireOutput 1 2 3 4 ; t0
)

NB. Next we define an 8-bit ALU using 4 bit adders.
NB. The ALU does addition when cin is 0 and
NB. subtraction when cin is 1.

eightBitALU =: monad define 
'a b cin' =. y.
a =. dtb a
b =. bitXor rank 1 cin,rank 0 dtb b
t0 =. fourBitAdder (4 5 6 7 from a) , (4 5 6 7 from b) , cin
t1 =. fourBitAdder (0 1 2 3 from a) , (0 1 2 3 from b) , wireOutput 0 ; t0
btd (wireOutput 0 1 2 3 4 ; t1) , wireOutput 1 2 3 4 ; t0
)