###---------------------------
# Program: 4 Bit Adder - Ring
# Author:  Bert Mariani
# Date:    2018-02-28
#
# Bit Adder: Input  A B Cin
#            Output S   Cout
#
# A ^ B => axb                XOR gate
#          axb ^ C => Sout    XOR gate
#          axb & C => d       AND gate
#
# A & B => anb                AND gate
#          anb | d => Cout     OR gate
#
# Call Adder for number of bit in input fields
###-------------------------------------------
### 4 Bits

Cout     = "0"
OutputS  = "0000"
InputA   = "0101"
InputB   = "1101"

   See "InputA:.. "+ InputA +nl
   See "InputB:.. "+ InputB +nl
BitsAdd(InputA, InputB)
   See "Sum...: "+ Cout +" "+ OutputS +nl+nl

###-------------------------------------------
### 32 Bits

Cout     = "0"
OutputS  = "00000000000000000000000000000000"
InputA   = "01010101010101010101010101010101"
InputB   = "11011101110111011101110111011101"

   See "InputA:.. "+ InputA +nl
   See "InputB:.. "+ InputB +nl
BitsAdd(InputA, InputB)
   See "Sum...: "+ Cout +" "+ OutputS +nl+nl

###-------------------------------

Func BitsAdd(InputA, InputB)
	nbrBits = len(InputA)
	
	for i = nbrBits to 1 step -1
	      A = InputA[i]
	      B = InputB[i]
	      C = Cout

              S = Adder(A,B,C)
	      OutputS[i] = "" + S
	next
return

###------------------------
Func Adder(A,B,C)

    axb  =   A ^ B
    Sout = axb ^ C
    d    = axb & C

    anb  =   A & B
    Cout = anb | d    ### Cout is global

return(Sout)
###------------------------