Generic primes generator

An example of how to implement a generic primes generator that you can use with any numerical type. Of course, performances will be impacted by your choice :

• howlongfor(intPrimes.drop(25000).head) // res0: (String, Int) = (459ms,287137)
• howlongfor(longPrimes.drop(25000).head) // res1: (String, Long) = (1349ms,287137)
• howlongfor(bigIntPrimes.drop(25000).head) // res2: (String, BigInt) = (4361ms,287137)

My primes project can be found here.

Simplified source code

	package experiments
	object Primes {
	class Generator[NUM](implicit numops: Integral[NUM]) {
	import annotation.tailrec
	import numops._
	private val two = one + one
	private val three = one + one + one
	private def sqrt(number: NUM) = { //https://issues.scala-lang.org/browse/SI-3739
	def next(n: NUM, i: NUM): NUM = (n + i / n) / two
	var n = one
	var n1 = next(n, number)
	while ((n1 - n).abs > one) {
	n = n1
	n1 = next(n, number)
	}
	while (n1 * n1 > number) {
	n1 -= one
	}
	n1
	}
	def isPrime(v: NUM): Boolean = {
	val upTo = sqrt(v)
	@tailrec
	def checkUpTo(from: NUM): Boolean = {
	if (v % from == 0) false
	else if (from == upTo) true else checkUpTo(from + one)
	}
	(v <= three) || checkUpTo(two)
	}
	def integers = {
	def next(cur: NUM): Stream[NUM] = cur #:: next(cur + one)
	next(one)
	}
	def candidates = integers.tail
	def primes =
	candidates
	.filter(isPrime(_))
	}
	def howlongfor[T](proc: => T): Tuple2[String, T] = {
	def now = System.currentTimeMillis
	now match {
	case start =>
	val result = proc
	(s"${now - start}ms", result)
	}
	}
	def intPrimes = (new Generator[Int]).primes
	def longPrimes = (new Generator[Long]).primes
	def bigIntPrimes = (new Generator[BigInt]).primes
	howlongfor(intPrimes.drop(25000).head) // res0: (String, Int) = (459ms,287137)
	howlongfor(longPrimes.drop(25000).head) // res1: (String, Long) = (1349ms,287137)
	howlongfor(bigIntPrimes.drop(25000).head) // res2: (String, BigInt) = (4361ms,287137)
	}

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