/*                                                                      
 Copyright 2019 Blue Liang, liangkangnan@163.com
                                                                         
 Licensed under the Apache License, Version 2.0 (the "License");         
 you may not use this file except in compliance with the License.        
 You may obtain a copy of the License at                                 
                                                                         
     http://www.apache.org/licenses/LICENSE-2.0                          
                                                                         
 Unless required by applicable law or agreed to in writing, software    
 distributed under the License is distributed on an "AS IS" BASIS,       
 WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 See the License for the specific language governing permissions and     
 limitations under the License.                                          
 */

`include "defines.v"


module div(

    input wire clk,
    input wire rst,

    input wire[`RegBus] dividend_i,
    input wire[`RegBus] divisor_i,
    input wire start_i,
    input wire[2:0] op_i,
    input wire[`RegAddrBus] reg_waddr_i,

    output reg[`DoubleRegBus] result_o,
	output reg ready_o,
    output wire busy_o,
    output reg[2:0] op_o,
    output reg[`RegAddrBus] reg_waddr_o

    );

    localparam STATE_IDLE = 0;
    localparam STATE_START = 1;
    localparam STATE_INVERT = 2;
    localparam STATE_END = 3;

    reg[`RegBus] dividend_temp;
    reg[`RegBus] divisor_temp;
    reg[1:0] state;
    reg[6:0] count;
    reg[`RegBus] div_result;
    reg[`RegBus] div_remain;
    reg[`RegBus] minuend;
    reg[`RegBus] divisor_zero_result;
    reg invert_result;


    assign busy_o = (state != STATE_IDLE)? `True : `False;


    always @ (posedge clk) begin
        if (rst == `RstEnable) begin
            state <= STATE_IDLE;
            ready_o <= `DivResultNotReady;
            result_o <= {`ZeroWord, `ZeroWord};
            div_result <= `ZeroWord;
            div_remain <= `ZeroWord;
            divisor_zero_result <= ~32'b00000001 + 1'b1;
            op_o <= 3'h0;
            reg_waddr_o <= `ZeroWord;
            dividend_temp <= `ZeroWord;
            divisor_temp <= `ZeroWord;
            invert_result <= 1'b0;
        end else begin
            case (state)
                STATE_IDLE: begin
                    if (start_i == `DivStart) begin
                        op_o <= op_i;
                        reg_waddr_o <= reg_waddr_i;

                        if (divisor_i == `ZeroWord) begin
                            ready_o <= `DivResultReady;
                            result_o <= {dividend_i, divisor_zero_result};
                        end else begin
                            count <= 7'd31;
                            state <= STATE_START;
                            div_result <= `ZeroWord;
                            div_remain <= `ZeroWord;

                            if ((op_i == `INST_DIV) || (op_i == `INST_REM)) begin
                                if (dividend_i[31] == 1'b1) begin
                                    dividend_temp <= ~dividend_i + 1;
                                    minuend <= ((~dividend_i + 1) >> 7'd31) & 1'b1;
                                end else begin
                                    dividend_temp <= dividend_i;
                                    minuend <= (dividend_i >> 7'd31) & 1'b1;
                                end
                                if (divisor_i[31] == 1'b1) begin
                                    divisor_temp <= ~divisor_i + 1;
                                end else begin
                                    divisor_temp <= divisor_i;
                                end
                            end else begin
                                dividend_temp <= dividend_i;
                                minuend <= (dividend_i >> 7'd31) & 1'b1;
                                divisor_temp <= divisor_i;
                            end

                            if (((op_i == `INST_DIV) && (dividend_i[31] ^ divisor_i[31] == 1'b1))
                                || ((op_i == `INST_REM) && (dividend_i[31] == 1'b1))) begin
                                invert_result <= 1'b1;
                            end else begin
                                invert_result <= 1'b0;
                            end
                        end
                    end else begin
                        ready_o <= `DivResultNotReady;
                        result_o <= {`ZeroWord, `ZeroWord};
                    end
                end

                STATE_START: begin
                    if (start_i == `DivStart) begin
                        if (count >= 7'd1) begin
                            if (minuend >= divisor_temp) begin
                                div_result <= (div_result << 1'b1) | 1'b1;
                                minuend <= ((minuend - divisor_temp) << 1'b1) | ((dividend_temp >> (count - 1'b1)) & 1'b1);
                            end else begin
                                div_result <= (div_result << 1'b1) | 1'b0;
                                minuend <= (minuend << 1'b1) | ((dividend_temp >> (count - 1'b1)) & 1'b1);
                            end
                            count <= count - 1'b1;
                        end else begin
                            state <= STATE_INVERT;
                            if (minuend >= divisor_temp) begin
                                div_result <= (div_result << 1'b1) | 1'b1;
                                div_remain <= minuend - divisor_temp;
                            end else begin
                                div_result <= (div_result << 1'b1) | 1'b0;
                                div_remain <= minuend;
                            end
                        end
                    end else begin
                        ready_o <= `DivResultReady;
                        result_o <= {`ZeroWord, `ZeroWord};
                        state <= STATE_IDLE;
                    end
                end

                STATE_INVERT: begin
                    if (start_i == `DivStart) begin
                        if (invert_result == 1'b1) begin
                            div_result <= ~div_result + 1'b1;
                            div_remain <= ~div_remain + 1'b1;
                        end
                        state <= STATE_END;
                    end else begin
                        ready_o <= `DivResultReady;
                        result_o <= {`ZeroWord, `ZeroWord};
                        state <= STATE_IDLE;
                    end
                end

                STATE_END: begin
                    if (start_i == `DivStart) begin
                        ready_o <= `DivResultReady;
                        result_o <= {div_remain, div_result};
                        state <= STATE_IDLE;
                    end else begin
                        state <= STATE_IDLE;
                        result_o <= {`ZeroWord, `ZeroWord};
                        ready_o <= `DivResultNotReady;
                    end
                end

            endcase
        end
    end

endmodule