Convert A Large Integer To a Hex String In Javascript

Question

I need to find a way to convert a large number into a hex string in javascript. Straight off the bat, I tried myBigNumber.toString(16) but if myBigNumber has a very large value (eg 1298925419114529174706173) then myBigNumber.toString(16) will return an erroneous result, which is just brilliant. I tried writing by own function as follows:

function (integer) {
    var result = '';

    while (integer) {
        result = (integer % 16).toString(16) + result;
        integer = Math.floor(integer / 16);
    }
}

However, large numbers modulo 16 all return 0 (I think this fundamental issue is what is causing the problem with toString. I also tried replacing (integer % 16) with (integer - 16 * Math.floor(integer/16)) but that had the same issue.

I have also looked at the Big Integer Javascript library but that is a huge plugin for one, hopefully relatively straightforward problem.

Any thoughts as to how I can get a valid result? Maybe some sort of divide and conquer approach? I am really rather stuck here.

Answer 1

Assuming you have your integer stored as a decimal string like '1298925419114529174706173':

function dec2hex(str){ // .toString(16) only works up to 2^53
    var dec = str.toString().split(''), sum = [], hex = [], i, s
    while(dec.length){
        s = 1 * dec.shift()
        for(i = 0; s || i < sum.length; i++){
            s += (sum[i] || 0) * 10
            sum[i] = s % 16
            s = (s - sum[i]) / 16
        }
    }
    while(sum.length){
        hex.push(sum.pop().toString(16))
    }
    return hex.join('')
}