mathjs/src/function/arithmetic/round.js

/**
 * Round a value towards the nearest integer
 *
 *     round(x)
 *     round(x, n)
 *
 * For matrices, the function is evaluated element wise.
 *
 * @param {Number | Complex | Array | Matrix} x
 * @param {Number | Array} [n] number of decimals (by default n=0)
 * @return {Number | Complex | Array | Matrix} res
 */
math.round = function round(x, n) {
  if (arguments.length != 1 && arguments.length != 2) {
    throw newArgumentsError('round', arguments.length, 1, 2);
  }

  if (n == undefined) {
    // round (x)
    if (isNumber(x)) {
      return Math.round(x);
    }

    if (x instanceof Complex) {
      return Complex.create (
          Math.round(x.re),
          Math.round(x.im)
      );
    }

    if (Array.isArray(x) || x instanceof Matrix) {
      return util.map(x, math.round);
    }

    if (x.valueOf() !== x) {
      // fallback on the objects primitive value
      return math.round(x.valueOf());
    }

    throw newUnsupportedTypeError('round', x);
  }
  else {
    // round (x, n)
    if (!isNumber(n)) {
      throw new TypeError('Number of decimals in function round must be an integer');
    }
    if (n !== Math.round(n)) {
      throw new TypeError('Number of decimals in function round must be integer');
    }
    if (n < 0 || n > 9) {
      throw new Error ('Number of decimals in function round must be in te range of 0-9');
    }

    if (isNumber(x)) {
      return roundNumber(x, n);
    }

    if (x instanceof Complex) {
      return Complex.create (
          roundNumber(x.re, n),
          roundNumber(x.im, n)
      );
    }

    if (Array.isArray(x) || x instanceof Matrix ||
        Array.isArray(n) || n instanceof Matrix) {
      return util.map2(x, n, math.round);
    }

    if (x.valueOf() !== x || n.valueOf() !== n) {
      // fallback on the objects primitive values
      return math.round(x.valueOf(), n.valueOf());
    }

    throw newUnsupportedTypeError('round', x, n);
  }
};

/**
 * round a number to the given number of decimals, or to zero if decimals is
 * not provided
 * @param {Number} value
 * @param {Number} [decimals]  number of decimals, between 0 and 15 (0 by default)
 * @return {Number} roundedValue
 */
function roundNumber (value, decimals) {
  if (decimals) {
    var p = Math.pow(10, decimals);
    return Math.round(value * p) / p;
  }
  else {
    return Math.round(value);
  }
}