@polkadot/util
Version:
A collection of useful utilities for @polkadot
33 lines (32 loc) • 1.19 kB
JavaScript
;
Object.defineProperty(exports, "__esModule", { value: true });
exports.nSqrt = nSqrt;
const x_bigint_1 = require("@polkadot/x-bigint");
const consts_js_1 = require("./consts.js");
const toBigInt_js_1 = require("./toBigInt.js");
/**
* @name nSqrt
* @summary Calculates the integer square root of a bigint
*/
function nSqrt(value) {
const n = (0, toBigInt_js_1.nToBigInt)(value);
if (n < consts_js_1._0n) {
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 <= consts_js_1._2pow53n) {
// ~~ is more performant that Math.floor
return (0, x_bigint_1.BigInt)(~~Math.sqrt(Number(n)));
}
// 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._sqrt2pow53n;
while (true) {
const x1 = ((n / x0) + x0) >> consts_js_1._1n;
if (x0 === x1 || (x0 === (x1 - consts_js_1._1n))) {
return x0;
}
x0 = x1;
}
}