prime?

prime.coffee

isPrime = (num)->
  # 整数チェック
  if Math.floor(num) isnt num then return false
  if num < 2 then return false
  if num is 2 then return true

  # 偶数は除いてチェック
  if num % 2 is 0 then return false
  for n in [3..Math.floor num/2] by 2 when num % n is 0 then return false
  # 素数発見
  true

getPrimes = (range) -> for num in [0...range] when isPrime num then num

module.exports =
  isPrime: isPrime
  getPrimes : getPrimes

# test
do ->
  console.time 'test'
  console.assert getPrimes(100000).length is 9592 , "getPrimes(10000).length 9592 is #{getPrimes(100000).length} "
  console.assert isPrime(2.2)  is false  , 'isPrime(2.2)  is false '
  console.assert isPrime(1)    is false  , 'isPrime(1)    is false '
  console.assert isPrime(2)    is true   , 'isPrime(2)    is true  '
  console.assert isPrime(3)    is true   , 'isPrime(3)    is true  '
  console.assert isPrime(4)    is false  , 'isPrime(4)    is false '
  console.assert isPrime(5)    is true   , 'isPrime(5)    is true  '
  console.assert isPrime(6)    is false  , 'isPrime(6)    is false '
  console.assert isPrime(7)    is true   , 'isPrime(7)    is true  '
  console.assert isPrime(8)    is false  , 'isPrime(8)    is false '
  console.assert isPrime(9)    is false  , 'isPrime(9)    is false '
  console.assert isPrime(10)   is false  , 'isPrime(10)   is false '
  console.assert isPrime(983)  is true   , 'isPrime(983)  is true  '
  console.assert isPrime(6473) is true   , 'isPrime(6473) is true  '
  console.assert isPrime(6479) is false  , 'isPrime(6479) is false '
  console.assert isPrime(209719) is true  , 'isPrime(209719) is true '
  console.timeEnd 'test'