@polkadot/util
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A collection of useful utilities for @polkadot
42 lines (41 loc) • 1.33 kB
JavaScript
;
Object.defineProperty(exports, "__esModule", { value: true });
exports.bnSqrt = bnSqrt;
const bn_js_1 = require("./bn.js");
const consts_js_1 = require("./consts.js");
const toBn_js_1 = require("./toBn.js");
/**
* @name bnSqrt
* @summary Calculates the integer square root of a BN
* @example
* <BR>
*
* ```javascript
* import BN from 'bn.js';
* import { bnSqrt } from '@polkadot/util';
*
* bnSqrt(new BN(16)).toString(); // => '4'
* ```
*/
function bnSqrt(value) {
const n = (0, toBn_js_1.bnToBn)(value);
if (n.isNeg()) {
throw new Error('square root of negative numbers is not supported');
}
// https://stackoverflow.com/questions/53683995/javascript-big-integer-square-root/
// shortcut <= 2^53 - 1 to use the JS utils
if (n.lte(consts_js_1.BN_MAX_INTEGER)) {
// ~~ More performant version of Math.floor
return new bn_js_1.BN(~~Math.sqrt(n.toNumber()));
}
// Use sqrt(MAX_SAFE_INTEGER) as starting point. since we already know the
// output will be larger than this, we expect this to be a safe start
let x0 = consts_js_1.BN_SQRT_MAX_INTEGER.clone();
while (true) {
const x1 = n.div(x0).iadd(x0).ishrn(1);
if (x0.eq(x1) || x0.eq(x1.sub(consts_js_1.BN_ONE))) {
return x0;
}
x0 = x1;
}
}