tough-rational/lib/functions/to-string.js

Rational class using BigInt with fallback to bignumber.js

'use strict';

const strip = require('../strip');
const util = require('../util');
const powGenerator = require('./pow-generator');
const pow = powGenerator();
const compat = require('../compat');

const PRECISION_PADDING = compat.testForBigInt() ? BigInt(1000) : 1000;

const maybeAddLeadingZero = (s) => {
  if (util.first(s) === '.') return '0' + s;
  return s;
};

const defaultToZero = (s) => !String(s) ? '0' : s;

const toString = ([ aNum, aDen ], [ bNum, bDen ]) => {
  const decimals = bNum / bDen;
  const zeroes = BigInt(decimals) + PRECISION_PADDING;
  const precisionCliff = pow(BigInt(10), zeroes);
  const factor = precisionCliff / aDen;
  const digits = [].slice.call(String(aNum * factor));
  const insertDecimalAt = digits.length - Number(zeroes);
  const joined = insertDecimalAt < 0 ? ['.'].concat(Array.apply(null, { length: Math.abs(insertDecimalAt) }).map(() => 0)).concat(digits).join('') : digits.slice(0, insertDecimalAt).concat('.').concat(digits.slice(insertDecimalAt)).join('');
  const decimalPosition = joined.lastIndexOf('.');
  if (!~decimalPosition) return maybeAddLeadingZero(strip.stripZeroes(joined));
  return defaultToZero(maybeAddLeadingZero(strip.stripZeroes(joined.substr(0, decimalPosition + 1 + Number(decimals)))));
};

module.exports = toString;