locutus/php/math/round.js

Locutus other languages' standard libraries to JavaScript for fun and educational purposes

'use strict';

function roundToInt(value, mode) {
  var tmp = Math.floor(Math.abs(value) + 0.5);

  if (mode === 'PHP_ROUND_HALF_DOWN' && value === tmp - 0.5 || mode === 'PHP_ROUND_HALF_EVEN' && value === 0.5 + 2 * Math.floor(tmp / 2) || mode === 'PHP_ROUND_HALF_ODD' && value === 0.5 + 2 * Math.floor(tmp / 2) - 1) {
    tmp -= 1;
  }

  return value < 0 ? -tmp : tmp;
}

module.exports = function round(value) {
  var precision = arguments.length > 1 && arguments[1] !== undefined ? arguments[1] : 0;
  var mode = arguments.length > 2 && arguments[2] !== undefined ? arguments[2] : 'PHP_ROUND_HALF_UP';

  //  discuss at: https://locutus.io/php/round/
  // original by: Philip Peterson
  //  revised by: Onno Marsman (https://twitter.com/onnomarsman)
  //  revised by: T.Wild
  //  revised by: Rafał Kukawski (https://blog.kukawski.pl)
  //    input by: Greenseed
  //    input by: meo
  //    input by: William
  //    input by: Josep Sanz (https://www.ws3.es/)
  // bugfixed by: Brett Zamir (https://brett-zamir.me)
  //  revised by: Rafał Kukawski
  //   example 1: round(1241757, -3)
  //   returns 1: 1242000
  //   example 2: round(3.6)
  //   returns 2: 4
  //   example 3: round(2.835, 2)
  //   returns 3: 2.84
  //   example 4: round(1.1749999999999, 2)
  //   returns 4: 1.17
  //   example 5: round(58551.799999999996, 2)
  //   returns 5: 58551.8
  //   example 6: round(4096.485, 2)
  //   returns 6: 4096.49

  var floatCast = require('../_helpers/_php_cast_float');
  var intCast = require('../_helpers/_php_cast_int');
  var p;

  // the code is heavily based on the native PHP implementation
  // https://github.com/php/php-src/blob/PHP-7.4/ext/standard/math.c#L355

  value = floatCast(value);
  precision = intCast(precision);
  p = Math.pow(10, precision);

  if (isNaN(value) || !isFinite(value)) {
    return value;
  }

  // if value already integer and positive precision
  // then nothing to do, return early
  if (Math.trunc(value) === value && precision >= 0) {
    return value;
  }

  // PHP does a pre-rounding before rounding to desired precision
  // https://wiki.php.net/rfc/rounding#pre-rounding_to_the_value_s_precision_if_possible
  var preRoundPrecision = 14 - Math.floor(Math.log10(Math.abs(value)));

  if (preRoundPrecision > precision && preRoundPrecision - 15 < precision) {
    value = roundToInt(value * Math.pow(10, preRoundPrecision), mode);
    value /= Math.pow(10, Math.abs(precision - preRoundPrecision));
  } else {
    value *= p;
  }

  value = roundToInt(value, mode);

  return value / p;
};
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