mathjs/lib/function/utils/isPrime.js

Math.js is an extensive math library for JavaScript and Node.js. It features a flexible expression parser with support for symbolic computation, comes with a large set of built-in functions and constants, and offers an integrated solution to work with dif

'use strict';

var deepMap = require('../../utils/collection/deepMap');

function factory(type, config, load, typed) {
  /**
   * Test whether a value is prime: has no divisors other than itself and one.
   * The function supports type `number`, `bignumber`.
   *
   * The function is evaluated element-wise in case of Array or Matrix input.
   *
   * Syntax:
   *
   *     math.isPrime(x)
   *
   * Examples:
   *
   *    math.isPrime(3)                     // returns true
   *    math.isPrime(-2)                    // returns false
   *    math.isPrime(0)                     // returns false
   *    math.isPrime(-0)                    // returns false
   *    math.isPrime(0.5)                   // returns false
   *    math.isPrime('2')                   // returns true
   *    math.isPrime([2, 17, 100])           // returns [true, true, false]
   *
   * See also:
   *
   *    isNumeric, isZero, isNegative, isInteger
   *
   * @param {number | BigNumber | Array | Matrix} x  Value to be tested
   * @return {boolean}  Returns true when `x` is larger than zero.
   *                    Throws an error in case of an unknown data type.
   */
  var isPrime = typed('isPrime', {
    'number': function number(x) {
      if (x < 2) {
        return false;
      }

      if (x === 2) {
        return true;
      }

      if (x % 2 === 0) {
        return false;
      }

      for (var i = 3; i * i <= x; i += 2) {
        if (x % i === 0) {
          return false;
        }
      }

      return true;
    },
    'BigNumber': function BigNumber(x) {
      if (x.lt(2)) {
        return false;
      }

      if (x.equals(2)) {
        return true;
      }

      if (x.mod(2).isZero()) {
        return false;
      }

      for (var i = type.BigNumber(3); i.times(i).lte(x); i = i.plus(1)) {
        if (x.mod(i).isZero()) {
          return false;
        }
      }

      return true;
    },
    'Array | Matrix': function ArrayMatrix(x) {
      return deepMap(x, isPrime);
    }
  });
  return isPrime;
}

exports.name = 'isPrime';
exports.factory = factory;