JavaScript Bitwise Masking

Question

This question is similar to this other question; however, I\'d like to understand why this is working as it is.

The following code:

console.log((pars         


        

Answer 1

Because bitwise operations (like &) are done on signed 32-bit integers in javascript. 0xFFFFFFFF, where all bits are set, is actually -1, and the 0xde000000 you are expecting is actually -570425344.

Answer 2

In JavaScript, all bitwise operations (and & among them) return signed 32-bit integer as a result, in the range −2³¹ through 2³¹−1, inclusive. That's why you have that extra bit (0xde000000 is greater than 0x7ffffff) representing a sign now, meaning that you get a negative value instead.

One possible fix:

var r = 0xdeadbeef & 0xff000000;
if (r < 0) {
  r += (1 << 30) * 4;
}
console.log( r.toString(16) ); // 'de000000'