How is the modulo operator implemented in the HotSpot JVM?

Question

I understand that the modulus operation can be optimised using a little & wise magic where the divisor is a power of 2...

• and presuma

Answer 1

Here is one sample code snippet

public class Test {

    public static void main(String[] args)  {
        int a=103;
        int b=5;
        int c=a%b;
        }
    }

Now if you see the compiled code of it You will see

public static void main(java.lang.String[]);
   flags: ACC_PUBLIC, ACC_STATIC
   Code:
     stack=2, locals=4, args_size=1
        0: bipush        103
        2: istore_1
        3: iconst_5
        4: istore_2
        5: iload_1
        6: iload_2
        7: irem
        8: istore_3
        9: return

bipush- push a byte onto the stack as an integer value ie 103

istore_1-Pops an int off the stack and stores it in local variable,in the current frame.

and in 3: iconst_5 constant integer is pushed onto the stack

istore_2 does the same as istore_1 just variable named changed.

Then 5: iload_1 and 6:iload_2 both the variables are again pushed onto stack for operations

now at 7:irem the remainder operator works which you are calling as modulo.

Now how does Remainder operators works. It's Pops two ints(value of a and b) off the operand stack, divides a by b , computes the remainder and pushes the int remainder back onto the stack. The remainder is (b - ((a / b) * b)). This is what is used by the % operator in Java.