Judging if a year is a leap year in Verilog code

[xofun]

Judge a leap year

Hi,all:
It is easy to achieve it in C code:

if(year%4==0 && year% 100!=0 || year%400==0 )

I want to transfer the C code to verilog code. Is there a function aviliable to judge a year can be divided exactly by 4,100,or 400?By right shift "year" with code "year>>1" for twice time,it is OK if i get 2 zeros.Then how about 100 and 400?

Best regards

 

[nand_gates]

Re: Judge a leap year

Here is the verilog code!

/*    leap years are all the years divisible by 4, 
      except that years divisible by 100 are not leap years, 
      but years divisible by 400 are leap years. 

Encoding the year:

      binary ? easy for divisible by 4,  
      but difficult for 100 and 400 (not powers of 2)

      BCD ? easy for 100, 
      but more difficult for 4, what about 400?

Parts:
      construct a circuit that determines if the year is divisible by 4
      construct a circuit that determines if the year is divisible by 100
      construct a circuit that determines if the year is divisible by 400
      combine the results of the previous three steps to yield the leap year flag

Reference :
       Contemporary logic design Randy H. Katz 2nd ed Chapter 5 
*/
 

module leap(/*AUTOARG*/
   // Outputs
   leap_year_flag, 
   // Inputs
   year
   );
   input [15:0] year; // years in 4 digit bcd
   output      leap_year_flag;

   wire        div_by_100, div_by_400;
   reg         div_by4;
   
   /* Divisible-by-4 circuit 
    Only need to look at low-order two digits of the year 
    all years ending in 00, 04, 08, 12, 16, 20, etc. are divisible by 4

    if tens digit is even, then divisible by 4 if ones digit is 0, 4, or 8
    if tens digit is odd, then divisible by 4 if the ones digit is 2 or 6.  
    Translates into the following Boolean expression 
    */
   always @(/*AS*/year) 
     if (year[4]) begin  //tens digit is odd
        div_by4 = (year[3:0] == 4'h2) | (year[3:0] == 4'h6);
     end else begin
        div_by4 = (year[3:0] == 4'h0) | (year[3:0] == 4'h4) | (year[3:0] == 4'h8);
     end

   /*
    Divisible-by-100 just requires checking that all bits of two low-order digits are all 0: 
    */
   assign      div_by_100 = (year[7:4] == 4'h0) & (year[3:0] == 4'h0);
   
   /*
    Divisible-by-400 combines the divisible-by-4 
    (applied to the thousands and hundreds digits) 
    and divisible-by-100 circuits 
    */
   assign      div_by_400 = div_by_100 & div_by4;

   assign      leap_year_flag = div_by4 & (~div_by_100) | div_by_400;
   
endmodule // leap

Hope this helps!