41. A "population count" circuit counts the number of '1's in an input vector. Build a population count circuit for a 255-bit input vector.

 1 module top_module( 
 2     input [254:0] in,
 3     output [7:0] out );
 4     
 5 //“popcount”电路计算输入向量中“1”的数量。为 255 位输入向量构建人口计数电路。
 6     always@(*)
 7         begin
 8             out = 0;
 9             for(int i = 0;i < 255;i++)
10                 out = out +in[i];
11         end
12     
13 endmodule

 

42. Create a 100-bit binary ripple-carry adder by instantiating 100 full addres. The adder adds two 100-bit numbers and a carry-in to produce a 100-bit sum and carry out. To encourage you to actually instantiate full adders, also output the carry-out from each full adder in the ripple-carry adder. cout[99] is the final carry-out from the last full adder, and is the carry-out you usually see.

 1 // Adder-100i 方法一  
 2 module top_module( 
 3     input [99:0] a, b,
 4     input cin,
 5     output [99:0] cout,
 6     output [99:0] sum );
 7     
 8     integer i;
 9     
10     always @ (*) begin
11         for(i = 0; i < 100; i = i + 1) begin
12             if(i == 0)
13                 {cout[i],sum[i]} = a[i] + b[i] + cin;
14             else
15                 {cout[i],sum[i]} = a[i] + b[i] + cout[i-1];
16         end            
17     end
18  
19 endmodule
20 
21 
22 // Adder100i 方法二
23 module top_module(
24     input [99:0] a,b,
25     input cin,
26     output [99:0] cout,
27     output [99:0] sum
28     );
29     
30     generate
31         genvar i;
32         for(i = 0; i < 100; i = i + 1) begin:addr100
33             if(i == 0)
34                 assign {cout[i],sum[i]} = a[i] + b[i] + cin;
35                 //Error: {cout[i],sum[i]} = a[i] + b[i] + cin;
36             else
37                 assign {cout[i],sum[i]} = a[i] + b[i] + cout[i-1];
38                 //Error: {cout[i],sum[i]} = a[i] + b[i] + cout[i-1];
39         end            
40     endgenerate
41  
42 endmodule

43. You are provided with a BCD one-digit adder named bcd_fadd that adds two BCD digits and carry-in, and produces a sum and carry-out.

module bcd_fadd (
    input [3:0] a,
    input [3:0] b,
    input     cin,
    output   cout,
    output [3:0] sum );

Instantiate 100 copies of bcd_fadd to create a 100-digit BCD ripple-carry adder. Your adder should add two 100-digit BCD numbers (packed into 400-bit vectors) and a carry-in to produce a 100-digit sum and carry out.

 1  //BCD-Adder：generate-for方法
 2  
 3  module top_module( 
 4      input [399:0] a, b,
 5      input cin,
 6      output cout,
 7      output [399:0] sum );
 8      
 9      
10      wire[99:0] cout1;
11      bcd_fadd add0(.a(a[3:0]),
12                    .b(b[3:0]),
13                    .cin(cin),
14                    .cout(cout1[0]),
15                    .sum(sum[3:0])
16                   );
17      
18      //这题题目要求只能用generate-for来做
19      genvar i;
20      generate
21          for( i = 0 ; i<=99 ; i = i + 1)begin:bcd_fadder
22              bcd_fadd inst(
23                  .a(a[4*i+3:4*i]),
24                  .b(b[4*i+3:4*i]),
25                  .cin(cout1[i-1]),
26                  .sum(sum[4*i+3:4*i]),
27                  .cout(cout1[i])
28              );
29          end
30      endgenerate
31      assign cout = cout1[99];
32  
33  endmodule
34  
35 //这段代码，我觉得写的没问题，但是编译不通过，报错如下：
36 //Error (10232): Verilog HDL error at top_module.v(23): index -1 cannot fall outside the declared range [99:0] for vector "cout1" 
37 　　//File: /home/h/work/hdlbits.3553395/top_module.v Line: 23