What is the different of bitwise operation between javascript and java

Question

I'm doing some code conversion from javascript to java. When starting process some bitwise operation, I found the behavior of the bitwise operation between javascript and java are so different. I'm relatively experienced in the JVM side, the operation seems normal for me. But in the javascript side, I'm kind of confusing. I have checked MDN on mozilla the demo listed seem normal for me, but I found some case, not as my expected.

Question:

Would you help to explain why the bitwise operation & in the code that I attached are so different in javascript and java?
Also, I know that my knowledge in javascript is not enough for me to perform some kind of code conversion between these two languages, is there any useful site that helps me have a better understanding on the bitwise operation or the data structure of numeric data in javascript?

Java code

        Long x = 4023233417L;
        System.out.println(String.format("%d => %s",x, Long.toBinaryString(x)));
        Long y = 2562383102L;
        System.out.println(String.format("%d => %s",y, Long.toBinaryString(y)));
        Long result = x & y;
        System.out.println(String.format("%d => %s",result, Long.toBinaryString(result)));

        //Output
        //4023233417 => 11101111110011011010101110001001
        //2562383102 => 10011000101110101101110011111110
        //2290649224 => 10001000100010001000100010001000

Javascript code

x= 4023233417
console.log(x.toString(2))
y = 2562383102
console.log(y.toString(2))
result = x & y
console.log(result.toString(2))
//Output
//11101111110011011010101110001001
//10011000101110101101110011111110
//-1110111011101110111011101111000

I expecting x & y should "10001000100010001000100010001000".

But in the javascript code, the result is: "-1110111011101110111011101111000"

Akshay Bande · Accepted Answer · 2019-11-10 05:29:36Z

1

In javascript, you can perform bitwise operations on 32-bit numbers only. Even javascript use IEEE 754 floating-point standard to represent the number. Bitwise operation can be performed on 32-bit number. Hence rest of the bits will get ignored.

To convert any number to its 32-bit representation, number | 0 with it. When javascript reads x & y it considers 32-bits of x and y and ignores other bits silently. In your case, the numbers on which you are performing bitwise are x = -271733879 and y = -1732584194.

The safe range for bitwise operations in Javascript is Math.pow(-2,31) (-2147483648, about -2.1 billion) to Math.pow(2,32)-1 (2147483647, about +2.1 billion).

x= 4023233417;
console.log(x.toString(2))
y = 2562383102 ;
console.log(y.toString(2));

result = x & y;

console.log(result.toString(2)); //-1110111011101110111011101111000

x = x | 0; //-271733879
y = y | 0; //-1732584194
console.log("32 bit x: " + x);
console.log("32 bit y: " + y);
result = x & y;

console.log(result.toString(2)); //-1110111011101110111011101111000

edited Nov 10, 2019 at 5:29

answered Nov 10, 2019 at 5:24

Akshay Bande

2,6052 gold badges17 silver badges34 bronze badges

Sign up to request clarification or add additional context in comments.

1 Comment

Xeth Hung Over a year ago

Thanks for your answer, it provides useful information.

Collectives™ on Stack Overflow

What is the different of bitwise operation between javascript and java

1 Answer 1

1 Comment

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

1 Comment

Your Answer

Sign up or log in

Post as a guest

Related