module exe (
  input  logic               clk,
  input  logic               rst,

  //-----------------
  // Decode Interface
  //-----------------
  input  logic               idu_exe_instrVld_ID,

  // Register Access
  input  logic               idu_exe_rs1Vld_ID,
  input  logic [REG_IDX-1:0] idu_exe_rs1Idx_ID,
  input  logic               idu_exe_rs2Vld_ID,
  input  logic [REG_IDX-1:0] idu_exe_rs2Idx_ID,

  // Branch Type
  input  logic               idu_exe_instrJmp_ID,
  input  logic               idu_exe_instrBr_ID,

  // ALU information
  input  alu_op_t            idu_exe_aluOp_ID,

  // Passthrough Information
  input  mem_op_t            idu_exe_instrMemOp_ID,
  input  mem_size_t          idu_exe_instrMemSize_ID,
  input  rd_data_sel_t       idu_exe_instrRdDataSel_ID,

  //-----------------
  // Memory Interface
  //-----------------
  // ALU Result information
  output logic [WORD_WID-1:0] exe_mem_aluOpOut_EXE,
  // Stall
  input  logic                mem_exe_stallVld_EXE,
  // Memory Information
  output mem_op_t             exe_mem_instrMemOp_EXE,
  output mem_size_t           exe_mem_instrMemSize_EXE,
  // Passthrough information
  output rd_data_sel_t        exe_mem_instrRdDataSel_EXE,

  //-----------------------
  // Fetch Branch Interface
  //-----------------------
  output logic                exe_ifu_brRes_EXE,
  output logic                exe_ifu_brTaken_EXE,
  output logic [WORD_WID-1:0] exe_ifu_brPC_EXE,

  //--------------------
  // Writeback Interface
  //--------------------
  input  logic                wb_exe_rdVld_WB,
  input  logic [REG_IDX-1:0]  wb_exe_rdIdx_WB,
  input  logic [WORD_WID-1:0] wb_exe_rdData_WB

);

  logic                instrVld_EXE;

  // Alu
  logic [WORD_WID-1:0] aluSumDiff_EXE;
  logic [WORD_WID-1:0] aluSumDiffIn1_EXE;
  logic [WORD_WID-1:0] aluSumDiffIn2_EXE;

  logic [WORD_WID-1:0] aluLeftShft_EXE;
  logic [WORD_WID-1:0] aluRightShft_EXE;
  logic [WORD_WID-1:0] aluRightShftUsign_EXE;
  logic [WORD_WID-1:0] aluRightShftSext_EXE;

  logic [WORD_WID-1:0] aluCmp_EXE;
  logic [WORD_WID-1:0] aluCmpSign_EXE;
  logic [WORD_WID-1:0] aluCmpUsign_EXE;
  logic                aluCmpMsbDiff_EXE;
  logic                aluCmpLowUsign_EXE;

  // Branch Resolution
  logic          [5:0] brResChoice_EXE;

  // Reg File
  logic [NUM_REG-1:1] [WORD_WID-1:0] regData_XXX;

  // Stall Signal
  assign stallVld_ID = exe_mem_instrVld_EXE & ~mem_exe_stallVld_EXE;

  //--------------------
  // Decode Output Flops
  //--------------------

  // Flop Decode information
  AFFR #(.WIDTH(1))        AFFR_EXE_instrVld (.q(exe_mem_instrVld_EXE), .d(idu_exe_instrVld_ID), .en(stallVld_ID), .clk(clk), rst(rst));
  AFF  #(.DTYPE(alu_op_t)) AFF_EXE_aluOp     (.q(idu_exe_aluOp_EXE),    .d(idu_exe_aluOp_ID),    .en(stallVld_ID), .clk(clk));
  AFF  #(.WIDTH(WORD_WID)) AFF_EXE_pc        (.q(idu_exe_pc_EXE),       .d(idu_exe_pc_ID),       .en(stallVld_ID), .clk(clk));
  AFF  #(.WIDTH(1))        AFF_EXE_instrJmp  (.q(idu_exe_instrJmp_EXE), .d(idu_exe_instrJmp_ID), .en(stallVld_ID), .clk(clk));
  AFF  #(.WIDTH(1))        AFF_EXE_brRes     (.q(idu_exe_brRes_EXE),    .d(brResNxt_EXEM1),      .en(stallVld_ID), .clk(clk));

  //--------------
  // Register File
  //--------------
  assign rs1WrFwd_ID = wb_exe_rdWrVld_WB & (idu_exe_rs1Idx_ID == wb_exe_rdIdx_WB);
  assign rs2WrFwd_ID = wb_exe_rdWrVld_WB & (idu_exe_rs2Idx_ID == wb_exe_rdIdx_WB);

  always_ff @(posedge clk) begin
    // RS1 Read Port with Forwarding
    if (instrRs1Vld_ID) begin
      if (idx_exe_rs1Idx == REG_IDX'0)                          // X0 Register
        idu_exe_rs1Data_EXE <= WORD_SIZE'0;
      else if (rs1WrFwd_ID) begin                               // Write Foward
        idu_exe_rs1Data_EXE <= wb_exe_rdData_WB;
      else                                                      // Normal Read
        idu_exe_rs1Data_EXE <= regData_XXX[idu_exe_rs1Idx_ID];
    end

    // RS2 Read Port with Forwarding
    if (instrRs2Vld_ID) begin
      if (idx_exe_rs2Idx == REG_IDX'0)                          // X0 Register
        idu_exe_rs2Data_EXE <= WORD_WID'0;
      else if (rs2WrFwd_ID) begin                               // Write Foward
        idu_exe_rs2Data_EXE <= wb_exe_rdData_WB;
      else                                                      // Normal Read
        idu_exe_rs2Data_EXE <= regData_XXX[idu_exe_rs1Idx_ID];
    end

    // RD Write Port
    if (wb_exe_rdWrVld_WB & (~|wb_exe_rdIdx_WB)) begin
      regData_XXX[wb_exe_rdIdx_WB] <= wb_exe_rdData_WB;
    end
  end

  //----
  // ALU
  //----

  // Operand Selection
  assign aluIn1_EXE = (aluOp_EXE.rs1Sel == PC)   ? pc_EXE :             // PC for AUIPC, JAL
                      (aluOp_EXE.rs1Sel == ZERO) ? WORD_WID'(0) :       // 0 for LUI
                                                   rs1Data_EXE;         // RS1 for other operations

  assign aluIn2_EXE = (aluOp_EXE.rs2Sel == RS2)  ? rs2Data_EXE :        // RS2 for R type operations
                                                   aluOp_EXE.immediate; // Immediate for all other operations

  // Two's complement negation of aluIn2 if func7 is set (subtract)
  assign aluSumDiffIn1_EXE = aluIn1_EXE;
  assign aluSumDiffIn2_EXE = ({WORD_WID{aluOp_EXE.func7}} ^ aluIn2_EXE) + aluOp_EXE.func7;
  assign aluSumDiff_EXE    = aluSumDiffIn1_EXE + aluSumDiffIn2_EXE;

  // Shifter, TODO: Explicit signed barrel shifter with sign bit
  assign aluRightShftUsign_EXE = aluIn1_EXE >> aluIn2_EXE[4:0];
  assign aluRightShftSext_EXE  = ~({WORD_WID{1'b1}} >> aluIn2_EXE[4:0]);
  assign aluRightShft_EXE      = aluRightShftUsgn_EXE | (aluRightShftSext_EXE & {WORD_WID{aluOp_EXE.func7}});

  FLIP #( .WIDTH(WORD_WID) ) EXE_aluLeftShft ( .in (aluRightShftUsign_EXE), .out(aluLeftShft_EXE) );

  // Set Less Than
  assign aluCmpMsbDiff_EXE = aluIn2_EXE ^ aluIn1_EXE;
  assign aluCmpLowUsign_EXE = aluIn1_EXE[WORD_WID-2:0] < aluIn2_EXE[WORD_WID-2:0];
  assign aluCmpSign_EXE        = aluCmpMsbDiff_EXE ? aluIn1_EXE[WORD_WID-1] : aluCmpLowUsign_EXE; // If diff signs (MSB) and in1 negative, then in1 < 0 < in2, else compare low bits
  assign aluCmpUSign_EXE       = aluCmpMsbDiff_EXE ? aluIn2_EXE[WORD_WID-1] : aluCmpLowUsign_EXE; // If diff MSB and MSB in2[31] == 1,     then in1 < in2,     else compare low bits

  // Bitwise Operations
  assign aluXor_EXE = aluIn1_EXE ^ aluIn2_EXE;
  assign aluOr_EXE = aluIn1_EXE | aluIn2_EXE;
  assign aluAnd_EXE = aluIn1_EXE & aluIn2_EXE;

  // ALU Operation Select
  assign aluOpRes_EXE[0] = aluSumDiff_EXE;
  assign aluOpRes_EXE[1] = aluLeftShft_EXE;
  assign aluOpRes_EXE[2] = {(WORD_WID - 1)'(0), aluCmpSign_EXE};
  assign aluOpRes_EXE[3] = {(WORD_WID - 1)'(0), aluCmpUSign_EXE};
  assign aluOpRes_EXE[4] = aluXor_EXE;
  assign aluOpRes_EXE[5] = aluRightShft_EXE;
  assign aluOpRes_EXE[6] = aluOr_EXE;
  assign aluOpRes_EXE[7] = aluAnd_EXE;

  EMUX #(
      .WIDTH (WORD_WID),
      .INPUTS(8)
  ) EMUX_exe_aluOpSel (
      .in (aluOpResults_EXE),
      .out(aluOpOut_EXE),
      .sel(aluOp_EXE.func3)
  );

  // rd is either PC from jump instr or alu output
  assign exe_mem_rdData_EXE = instrJmp_EXE ? pc_EXE : aluOpOut_EXE;

  //------------------
  // Branch Resolution
  //------------------
  assign exe_ifu_brPC_EXE    = aluOpOut_EXE;
  assign exe_ifu_brRes_EXE   = brRes_EXE;
  assign exe_ifu_brTaken_EXE = (brTaken_EXE & idu_exe_instrBr_ID) | idu_exe_instrJmp_ID;


  assign brResChoice_EXE[0] = ~|aluXor_EXE;
  assign brResChoice_EXE[1] =  |aluXor_EXE;
  assign brResChoice_EXE[2] =   aluCmpSign_EXE;
  assign brResChoice_EXE[3] =  ~aluCmpSign_EXE;
  assign brResChoice_EXE[4] =   aluCmpUSign_EXE;
  assign brResChoice_EXE[5] =  ~aluCmpUSign_EXE;

  EMUX #(
      .WIDTH (1),
      .INPUTS(6)
  ) EMUX_exe_aluOpSel (
      .in (brResChoice_EXE),
      .out(brTaken_EXE),
      .sel(idu_exe_brOp_ID)
  );

  //---------------------
  // Pipeline passthrough
  //---------------------

  // Memory
  AFF #(.DTYPE(mem_op_t)) AFF_EXE_instRdDataSel (
    .q(exe_mem_instrMemOp_EXE),
    .d(idu_exe_instrMemOp_ID),
    .en(stallVld_ID),
    .clk(clk)
  );

  AFF #(.DTYPE(mem_op_size_t)) AFF_EXE_instMemSize (
    .q(exe_mem_instrMemSize_EXE),
    .d(idu_exe_instrMemSize_ID),
    .en(stallVld_ID),
    .clk(clk)
  );

  // Write Back
  AFF #(.DTYPE(rd_data_sel_t)) AFF_EXE_instRdDataSel (
    .q(exe_mem_instrRdDataSel_EXE),
    .d(idu_exe_instrRdDataSel_ID),
    .en(stallVld_ID),
    .clk(clk)
  );

endmodule