fox32-hw/verilog-src/alu.v

/*
  A and B are inputs, O is out
  OP is the operation to perform:
    000 = add
    001 = sub
    010 = mul_lo
    011 = mul_hi
    (011)
    100 = and
    101 = or
    110 = xor
    111 = not A
*/
module alu(
  input [31:0] A,
  input [31:0] B,
  input [2:0] op,
  output [31:0] O,
  output Fflow,
  output Fzero
);

wire [31:0] adder_out;

begin
  wire subtraction = op == 3'b001;
  wire [31:0] adder_B = subtraction ? ~B : B;
  wire adder_cout;

  carry_select_adder a(A, adder_B, subtraction, adder_out, adder_cout);
  assign Fflow = subtraction ? ~adder_cout : adder_cout;
end

wire [31:0] mult_out_hi;
wire [31:0] mult_out_lo;
multiplier mult(A, B, mult_out_hi, mult_out_lo);

assign O =
  op == 3'b000 ? adder_out :
  op == 3'b001 ? adder_out :
  op == 3'b010 ? mult_out_hi :
  op == 3'b011 ? mult_out_lo :
  op == 3'b100 ? A & B :
  op == 3'b101 ? A | B :
  op == 3'b110 ? A ^ B :
  op == 3'b111 ? ~A :
  '0;

assign Fzero = ~ (| O);

endmodule