module FPCVT(D, S, E, F);
    input wire [11:0] D;

    output reg S;
    output reg [2:0] E;
    output reg [3:0] F;

    reg out_of_range;
    reg round_bit;
    reg [11:0] D2;
    integer i;
    integer zero_count;

    always @* begin
        D2 = D;

        S = D2 >> 11; // Get the sign bit of the input number D
        D2 = S == 1 ? ~D2 + 1 : D2; // If negative, invert the bits and add 1 (get the magnitude)

        zero_count = 0; // count how many leading zeros
        for(i=11; i>=0 && ~D2[i]; i=i-1) begin
            zero_count=zero_count+1;
        end

        E = zero_count >= 8 ? 0 : 8 - zero_count; // calculate the exponent

        if (E != 0) begin
            for (i = 0; i < 4; i = i + 1) begin // calculate the significand
                F[i] = D2[8-zero_count+i];
            end
        end else begin
            for (i = 0; i < 4; i = i + 1) begin
                F[i] = D2[i]; // least significant 4 bits
            end
        end

        out_of_range = 0;
        round_bit = D2[7-zero_count]; // what happens if no 5th bit?
        if (round_bit) begin
            if (F == 4'b1111) begin // need to increase exponent
                if (E == 3'b111) begin
                    out_of_range = 1;
                end else begin
                    E = E+1;
                end
                F = 4'b1000; // 1111 + 1 = 10000 then shift to 1000
            end else begin
                F = F+1;
            end
        end

        // note: our range should be 1_111_1111 = -1920 to 0_111_1111 = 1920
        // i guess we could hard code those limits . . .
        if (out_of_range || D == 100000000000) begin
            F = 15;
            E = 7;
        end
    end
endmodule

module FPCVT_testbench();
    wire S;
    wire [2:0] E;
    wire [3:0] F;
    wire [11:0] D;
    assign D = 12'b000000101100;

    FPCVT myFPCVT(D, S, E, F);

    always @* begin
      $display("%b",D);
      $display("%b",S);
      $display("%b",E);
      $display("%b",F);
    end
endmodule