arithmetic.v

4位alu

module arithmetic(a,b,c0,S1,S0,g,cout);
input [3:0] a,b;
input c0;
input S1,S0;
output [3:0] g;

output cout;
reg cout;

wire [3:0] a,b;
wire c0,S1,S0; 
reg [3:0] g;

reg [4:0] result;       // ALU result 
reg [3:0] ctl;

always @(a or b or c0 or S1 or S0 )
begin
 result = alu_out(a,b,c0,ctl); 
 g    = result[3:0]; 
 cout  = result[4] ; 
 ctl= {S1,S0,c0};
 end



function [4:0] alu_out; 
input  [3:0] a,b ; 
input        c0 ; 
input  [3:0] ctl ; 



begin
    case (ctl)
        3'b000:  alu_out=a;          //Transfer
        3'b001:  alu_out=a+1;        //Increase
        3'b010:  alu_out=a+b;        //Addition
        3'b011:  alu_out=a+b+1;     //Increment the sum of a and b by 1
        3'b100:  alu_out=a+(~b);     //a plus one`s complement of b
        3'b101:  alu_out=a+(~b)+1;   //a minus b
        3'b110:  alu_out=(~a)+b;     //b plus one`s complement of a
        3'b111:  alu_out=(~a)+b+1;   //b minus a
        default: begin
            $display("unknown opcode");
             alu_out=5'bxxxxx;
        end
endcase
end
endfunction 



endmodule