How to divide by huge number

Question

I am trying to do this:

const numerator = 268435456;
const denominator = 2 ** 64;
const decimalFraction = numerator / denominator;

To make this work, I have tried to use the code suggested here: https://stackoverflow.com/a/54409977/3846032:

const rawValue = 268435456n;
const exponent = 2n ** 64n;
const precision = 100_000_000;
const fraction = Number((rawValue * BigInt(precision)) / exponent) / precision;

When I run this in dev it works fine, but in prod I get this error:

Uncaught TypeError: can't convert BigInt to number

I believe it is coming from 2n ** 64n.

I'm using create-react-app and some digging reveals this: https://github.com/facebook/create-react-app/issues/6907#issuecomment-778178677).

Unfortunately this suggestion makes it fail in both dev and prod with an OOM error.

Any suggestions on how to make this work would be appreciated.

Why are you still using normal numbers with BigInt? `precision` should use BigInt as well: `100_000_000n`, so then you'd just use `(rawValue * precision) / exponent / precision`. — kelsny, Jan 09 '23 at 16:39
Because I want to get a decimal `number` at the end of this. Regardless, if I try what you suggest, unfortunately I still get the same problem with the OOM. — Daniel Porteous, Jan 09 '23 at 16:41
`268435456 / Math.pow(2, 64)` gives me the expected `1.4551915228366852e-11` in my react-app — 0stone0, Jan 09 '23 at 16:45
Ahhh, the OOM was a problem later in the code, my bad. Let me write an answer summarizing what to do. — Daniel Porteous, Jan 09 '23 at 16:56
You'll need more than `100_000_000` for the precision because the quotient of your example is on the order of 1e-11. In other words, even if your example worked, it would display 0. e.g.: `Number((268435456n * 100_000_000n) / 2n ** 64n) / 100_000_000` is `0`. but `Number((268435456n * 100_000_000_000n) / 2n ** 64n) / 100_000_000_000` is `1e-11` — Wyck, Jan 09 '23 at 17:40

score 0 · Answer 1 · answered Jan 09 '23 at 16:58

Use Math.pow(2, 64) instead of 2 ** 64:

const Example = () => {

    const x = 268435456;
    const y = Math.pow(2, 64);

    return (x / y);
}

ReactDOM.render(<Example />, document.getElementById("react"));

<script src="https://cdnjs.cloudflare.com/ajax/libs/react/17.0.1/umd/react.production.min.js"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/react-dom/17.0.1/umd/react-dom.production.min.js"></script>
<div id="react"></div>

Daniel Porteous · Answer 2 · 2023-01-09T17:02:34.183

0

So it turns out the OOM I was getting was unrelated to this particular problem, so disregard that part.

As for this error:

Uncaught TypeError: can't convert BigInt to number

You can avoid it by doing Math.power(2, 64) instead of 2n ** 64n.

The issue in question: https://github.com/facebook/create-react-app/issues/11705.

edited Jan 09 '23 at 17:02

answered Jan 09 '23 at 16:58

Daniel Porteous

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You probably mean `2n ** 64n` and not `2 ** 64`. `2 ** 64` should be equivalent to `Math.pow(2, 64)`. – Marco Jan 09 '23 at 17:00
Yes true, my mistake, updated! – Daniel Porteous Jan 09 '23 at 17:02

How to divide by huge number

2 Answers2