hdlbits-Adder100i

Adder100i

Create a 100-bit binary ripple-carry adder by instantiating 100 full adders. The adder adds two 100-bit numbers and a carry-in to produce a 100-bit sum and carry out. To encourage you to actually instantiate full adders, also output the carry-out from each full adder in the ripple-carry adder. cout[99] is the final carry-out from the last full adder, and is the carry-out you usually see.

Hint

There are many full adders to instantiate. An instance array or generate statement would help here.

solution

module top_module( 
    input [99:0] a, b,
    input cin,
    output [99:0] cout,
    output [99:0] sum );
    
    assign cout[0] = a[0] & b[0] | a[0] & cin | b[0] & cin;
    assign sum[0]  = a[0] ^ b[0] ^ cin;
    
    always @(*) begin
        for (integer i = 1; i < 100; i++) begin
            cout[i] = a[i] & b[i] | a[i] & cout[i-1] | b[i] & cout[i-1];
            sum[i]  = a[i] ^ b[i] ^ cout[i-1];
        end
    end
endmodule