Add implementation in Crystal

Author: Ary Borenszweig

crystal/sieve.cr

@@ -0,0 +1,79 @@
+class Natural
+  @cnt = 1
+
+  def next
+    @cnt += 1
+  end
+end
+
+class Filter
+  getter number
+  property! next : Filter
+  property! last : Filter
+
+  def initialize(@number : Int32)
+    @last = self
+  end
+
+  def accept_and_add(n)
+    filter = self
+    upto = Math.sqrt(n)
+    loop do
+      if n.divisible_by?(filter.number)
+        return false
+      end
+      if filter.number > upto
+        new_filter = Filter.new(n)
+        last.next = new_filter
+        @last = new_filter
+        return true
+      end
+      filter = filter.next
+    end
+  end
+end
+
+class Primes
+  @natural = Natural.new
+
+  def next
+    loop do
+      n = @natural.next
+      filter = @filter
+      unless filter
+        @filter = Filter.new(n)
+        return n
+      end
+      if filter.accept_and_add(n)
+        return n
+      end
+    end
+  end
+
+  def compute
+    start = Time.now
+    cnt = 0
+    prnt_cnt = 97
+    res = 0
+    loop do
+      res = self.next
+      cnt += 1
+
+      if cnt.divisible_by?(prnt_cnt)
+        took = Time.now - start
+        puts "Computed #{cnt} primes in #{took.milliseconds} ms. Last one is #{res}"
+        prnt_cnt *= 2
+      end
+      break if cnt >= 100000
+    end
+    res
+  end
+end
+
+loop do
+  p = Primes.new
+  time = Time.now
+  p.compute
+  took = Time.now - time
+  puts "Hundred thousand primes computed in #{took.milliseconds}ms"
+end