请用verilog写一段2进制bcd码转10进制

以下是一种可能的实现方式，使用了递归和模块化的思想：

module bcd2dec(
    input [3:0] bcd,
    output reg [3:0] dec
);

always @(*) begin
    case (bcd)
        4'b0000: dec = 4'b0000;
        4'b0001: dec = 4'b0001;
        4'b0010: dec = 4'b0010;
        4'b0011: dec = 4'b0011;
        4'b0100: dec = 4'b0100;
        4'b0101: dec = 4'b0101;
        4'b0110: dec = 4'b0110;
        4'b0111: dec = 4'b0111;
        4'b1000: dec = 4'b1000;
        4'b1001: dec = 4'b1001;
        default: dec = 4'b0000; // in case of invalid input
    endcase
end

endmodule


module bcd2dec_recursive(
    input [n:0] bcd,
    input n,
    output reg [n:0] dec
);

// base case: when n = 0 (i.e., only one digit left)
// convert the last BCD digit to decimal
// and assign it to the least significant bit of the output
// then return
assign dec[0] = bcd2dec(bcd[3:0]);
assign dec[1:n] = 0; // clear the rest of the bits
if (n == 0) begin
    return;
end

// recursive case: when n > 0 (i.e., more than one digit left)
// recursively convert the higher order BCD digits to decimal,
// multiply each result by the appropriate power of 10,
// and add them all up to get the final decimal value
// then assign it to the output and return
reg [n-1:0] dec_higher; // intermediate result for higher order digits
bdc2dec_recursive #(.n(n-1)) (
    .bcd(bcd[3:n]),
    .dec(dec_higher)
);
assign dec = {dec_higher * 10, dec[3:0]};
end

endmodule

上述代码中，`bcd2dec` 模块实现了将单个BCD码转换为十进制数的功能。`bcd2dec_recursive` 模块则实现了将多位BCD码转换为十进制数的功能，其基本思路是：将最高位BCD码转换为十进制数；然后将其余高位BCD码转换为十进制数，乘以10的相应次幂，再加上最高位的十进制数，即可得到最终结果。递归过程中，每次调用都会将BCD码的位数减1，直到只剩下最后一位为止。