How to do bitwise AND in javascript on variables that are longer than 32 bit?

Question

I have 2 numbers in javascript that I want to bit and. They both are 33bit long

in C#:

 ((4294967296 & 4294967296 )==0) is false 

but in javascript:

 ((4294967296 & 4294967296 )==0) is true 

4294967296 is ((long)1) << 32

As I understand it, it is due to the fact that javascript converts values to int32 when performing bit wise operations.

How do I work around this? Any suggestions on how to replace bit and with a set of other math operations so that bits are not lost?

Answer 1

Here's a fun function for arbitrarily large integers:

function BitwiseAndLarge(val1, val2) {     var shift = 0, result = 0;     var mask = ~((~0) << 30); // Gives us a bit mask like 01111..1 (30 ones)     var divisor = 1 << 30; // To work with the bit mask, we need to clear bits at a time     while( (val1 != 0) && (val2 != 0) ) {         var rs = (mask & val1) & (mask & val2);         val1 = Math.floor(val1 / divisor); // val1 >>> 30         val2 = Math.floor(val2 / divisor); // val2 >>> 30         for(var i = shift++; i--;) {             rs *= divisor; // rs << 30         }         result += rs;     }     return result; } 

Assuming that the system handles at least 30-bit bitwise operations properly.

Answer 2

You could split each of the vars into 2 32-bit values (like a high word and low word), then do a bitwise operation on both pairs.

The script below runs as a Windows .js script. You can replace WScript.Echo() with alert() for Web.

var a = 4294967296; var b = 4294967296;  var w = 4294967296; // 2^32  var aHI = a / w; var aLO = a % w; var bHI = b / w; var bLO = b % w;  WScript.Echo((aHI & bHI) * w + (aLO & bLO));