marcandre	2015-06-09 12:32:11 +0900 (Tue, 09 Jun 2015)

  New Revision: 50802

  http://svn.ruby-lang.org/cgi-bin/viewvc.cgi?view=revision&revision=50802

  Log:
    * lib/prime.rb: Simplify and optimize EratosthenesSieve

  Modified files:
    trunk/lib/prime.rb
Index: lib/prime.rb
===================================================================
--- lib/prime.rb	(revision 50801)
+++ lib/prime.rb	(revision 50802)
@@ -424,10 +424,11 @@ class Prime https://github.com/ruby/ruby/blob/trunk/lib/prime.rb#L424
       segment_max = [segment_min + max_segment_size, max_cached_prime * 2].min
       root = Integer(Math.sqrt(segment_max).floor)
 
-      sieving_primes = @primes[1 .. -1].take_while { |prime| prime <= root }
-
       segment = ((segment_min + 1) .. segment_max).step(2).to_a
-      sieving_primes.each do |prime|
+
+      (1..Float::INFINITY).each do |sieving|
+        prime = @primes[sieving]
+        break if prime > root
         composite_index = (-(segment_min + 1 + prime) / 2) % prime
         while composite_index < segment.size do
           segment[composite_index] = nil

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