`default_nettype none
module serv_alu
  (
   input wire 	    clk,
   input wire 	    i_rst,
   input wire 	    i_en,
   input wire 	    i_rs1,
   input wire 	    i_op_b,
   input wire 	    i_buf,
   input wire 	    i_init,
   input wire 	    i_cnt_done,
   input wire 	    i_sub,
   input wire [1:0] i_bool_op,
   input wire 	    i_cmp_eq,
   input wire 	    i_cmp_uns,
   output wire 	    o_cmp,
   input wire 	    i_shamt_en,
   input wire 	    i_sh_right,
   input wire 	    i_sh_signed,
   output wire 	    o_sh_done,
   input wire [1:0] i_rd_sel,
   output wire 	    o_rd);

`include "serv_params.vh"

   wire        result_add;
   wire        result_eq;
   wire        result_lt;
   wire        result_sh;

   reg 	       result_lt_r;

   wire [4:0]  shamt;
   reg 	       shamt_msb;

   reg         en_r;
   wire        shamt_ser;
   wire        plus_1;
   wire        b_inv_plus_1;

   assign shamt_ser = i_sh_right ? i_op_b : b_inv_plus_1;

   shift_reg #(.LEN (5)) shamt_reg
     (.clk (clk),
      .i_rst (i_rst),
      .i_en (i_shamt_en),
      .i_d  (shamt_ser),
      .o_q  (shamt[0]),
      .o_par (shamt[4:1]));

   ser_shift shift
     (
      .i_clk (clk),
      .i_load (i_init),
      .i_shamt (shamt),
      .i_shamt_msb (shamt_msb),
      .i_signbit (i_sh_signed & i_rs1),
      .i_right  (i_sh_right),
      .o_done   (o_sh_done),
      .i_d (i_buf),
      .o_q (result_sh));

   wire        b_inv_plus_1_cy;

   always @(posedge clk)
     if (i_shamt_en)
       shamt_msb <= b_inv_plus_1_cy;

   ser_add ser_add_inv_plus_1
     (
      .clk (clk),
      .rst (i_rst),
      .a   (~i_op_b),
      .b   (plus_1),
      .clr (!i_en),
      .q   (b_inv_plus_1),
      .o_v (b_inv_plus_1_cy));

   wire       add_b = i_sub ? b_inv_plus_1 : i_op_b;

   ser_add ser_add
     (
      .clk (clk),
      .rst (i_rst),
      .a   (i_rs1),
      .b   (add_b),
      .clr (!i_en),
      .q   (result_add),
      .o_v ());

   ser_lt ser_lt
     (
      .i_clk (clk),
      .i_a   (i_rs1),
      .i_b   (i_op_b),
      .i_clr (!i_init),
      .i_sign (i_cnt_done & !i_cmp_uns),
      .o_q   (result_lt));

   assign plus_1 = i_en & !en_r;
   assign o_cmp = i_cmp_eq ? result_eq : result_lt;

   localparam [15:0] BOOL_LUT = 16'h8E96;//And, Or, =, xor
   wire result_bool = BOOL_LUT[{i_bool_op, i_rs1, i_op_b}];

   assign o_rd = (i_rd_sel == ALU_RESULT_ADD) ? result_add :
                 (i_rd_sel == ALU_RESULT_SR)  ? result_sh :
                 (i_rd_sel == ALU_RESULT_LT)  ? result_lt_r & plus_1:
                 (i_rd_sel == ALU_RESULT_BOOL) ? result_bool : 1'bx;


   reg 	eq_r;

   always @(posedge clk) begin
      if (i_init) begin
	 result_lt_r <= result_lt;
	 eq_r <= result_eq;
      end else begin
	 eq_r <= 1'b1;
      end
      en_r <= i_en;
   end

   assign result_eq = eq_r & (i_rs1 == i_op_b);

endmodule