mathjs/src/function/utils/isPrime.js

'use strict'

const 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.
   */
  const isPrime = typed('isPrime', {
    'number': function (x) {
      if (x < 2) {
        return false
      }
      if (x === 2) {
        return true
      }
      if (x % 2 === 0) {
        return false
      }
      for (let i = 3; i * i <= x; i += 2) {
        if (x % i === 0) {
          return false
        }
      }
      return true
    },

    'BigNumber': function (x) {
      if (x.lt(2)) {
        return false
      }
      if (x.equals(2)) {
        return true
      }
      if (x.mod(2).isZero()) {
        return false
      }
      for (let 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 (x) {
      return deepMap(x, isPrime)
    }
  })

  return isPrime
}

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