Javascript summing large integers

Question

In javascript I would like to create the binary hash of a large boolean array (54 elements) with the following method:

function bhash(arr) {
   for (var i = 0, L = arr.length, sum = 0; i < L; sum += Math.pow(2,i)*arr[i++]); 
   return sum;
}

In short: it creates the smallest integer to store an array of booleans in. Now my problem is that javascript apparently uses floats as default. The maximum number I have to create is 2^54-1 but once javascript reaches 2^53 it starts doing weird things:

9007199254740992+1 = 9007199254740994

Is there any way of using integers instead of floats in javascript? Or large integer summations?

Answer 1

Javascript uses floating point internally.

What is JavaScript's highest integer value that a Number can go to without losing precision?

In other words you can't use more than 53 bits. In some implementations you may be limited to 31.

Try storing the bits in more than one variable, use a string, or get a bignum library, or if you only need to deal with integers, a biginteger library.

Answer 2

javascript now has experimental support for BigInt.
At the time of writing only chrome supports this.

caniuse has no entry yet.

BigInt can be either used with a constructor, e.g. BigInt(20) or by appending n, e.g. 20n

Example:

const max = Number.MAX_SAFE_INTEGER;

console.log('javascript Number limit reached', max + 1 === max + 2) // true;

console.log('javascript BigInt limit reached', BigInt(max) + 1n === BigInt(max) + 2n); // false

Answer 3

BigInt is being added as a native feature of JavaScript.

typeof 123;
// → 'number'
typeof 123n;
// → 'bigint'

Example:

const max = BigInt(Number.MAX_SAFE_INTEGER);
const two = 2n;
const result = max + two;
console.log(result);
// → '9007199254740993'

Answer 4

No. Javascript only has one numeric type. You've to code yourself or use a large integer library (and you cannot even overload arithmetic operators).

Answer 5

Another implementation of large integer arithmetic (also using BigInt.js) is available at www.javascripter.net/math/calculators/100digitbigintcalculator.htm. Supports the operations + - * / as well as remainder, GCD, LCM, factorial, primality test, next prime, previous prime.

Answer 6

There are various BigInteger Javascript libraries that you can find through googling. e.g. http://www.leemon.com/crypto/BigInt.html

Answer 7

you're probably running into a byte length limit on your system. i'd take the array of booleans, convert it to an array of binary digits ([true, false, true] => [1,0,1]), then join this array into a string "101", then use parseInt('101',2), and you'll have your answer.

Answer 8

Here's (yet another) wrapper around Leemon Baird's BigInt.js

It is used in this online demo of a big integer calculator in JavaScript which implements the usual four operations + - * /, the modulus (%), and four builtin functions : the square root (sqrt), the power (pow), the recursive factorial (fact) and a memoizing Fibonacci (fibo).