`include "macros.v"

module alu1 (clk, 
             a_r,    a_a_,  a_d,
             op_r,   op_a_, op_d,
             out_r_, out_a, out_d_);

  input  clk;
  `input(a_r,    a_a,    a_a_,  [(`DATAWIDTH-1):0], a_d)
  `input(op_r,   op_a,   op_a_, [(`DATAWIDTH-1):0], op_d)
  `output(out_r, out_r_, out_a, [(`DATAWIDTH-1):0], out_d_)
  `defreg(out_d_, [(`DATAWIDTH-1):0], out_d)

  reg                    have_a;
  reg [(`DATAWIDTH-1):0] reg_a;
  reg                    have_op;
  reg [(`DATAWIDTH-1):0] reg_op;

  always @(posedge clk) begin
    if (!have_a) begin
      `onread(a_r, a_a) have_a = 1; reg_a = a_d; end
      end
    if (!have_op) begin
      `onread(op_r, op_a) have_op = 1; reg_op = op_d; end
      end
  
    if (have_a && have_op) begin
      case (reg_op)
        0: out_d = -reg_a;
        1: out_d = reg_a+1;
        2: out_d = reg_a-1;
        3: out_d = (reg_a<0) ? (-reg_a) : reg_a;
        default: out_d = 0;
      endcase        
      `onwrite(out_r, out_a)
        have_a  = 0;
        have_op = 0;
      end
    end
  end

endmodule