bitwise AND in Javascript with a 64 bit integer

Question

I am looking for a way of performing a bitwise AND on a 64 bit integer in JavaScript.

JavaScript will cast all of its double values into signed 32-bit integers to do

Answer 1

Javascript doesn't support 64 bit integers out of the box. This is what I ended up doing:

1. Found long.js, a self contained Long implementation on github.
2. Convert the string value representing the 64 bit number to a Long.
3. Extract the high and low 32 bit values
4. Do a 32 bit bitwise and between the high and low bits, separately
5. Initialise a new 64 bit Long from the low and high bit
6. If the number is > 0 then there is correlation between the two numbers

Note: for the code example below to work you need to load long.js.

// Handy to output leading zeros to make it easier to compare the bits when outputting to the console
function zeroPad(num, places){
    var zero = places - num.length + 1;
  return Array(+(zero > 0 && zero)).join('0') + num;
}

// 2^3 = 8
var val1 = Long.fromString('8', 10);
var val1High = val1.getHighBitsUnsigned();
var val1Low = val1.getLowBitsUnsigned();

// 2^61 = 2305843009213693960
var val2 = Long.fromString('2305843009213693960', 10);
var val2High = val2.getHighBitsUnsigned();
var val2Low = val2.getLowBitsUnsigned();

console.log('2^3 & (2^3 + 2^63)')
console.log(zeroPad(val1.toString(2), 64));
console.log(zeroPad(val2.toString(2), 64));

var bitwiseAndResult = Long.fromBits(val1Low & val2Low, val1High & val2High, true);

console.log(bitwiseAndResult);
console.log(zeroPad(bitwiseAndResult.toString(2), 64));
console.log('Correlation betwen val1 and val2 ?');
console.log(bitwiseAndResult > 0);

Console output:

2^3

0000000000000000000000000000000000000000000000000000000000001000

2^3 + 2^63

0010000000000000000000000000000000000000000000000000000000001000

2^3 & (2^3 + 2^63)

0000000000000000000000000000000000000000000000000000000000001000

Correlation between val1 and val2?

true