marcandre	2015-06-09 11:45:31 +0900 (Tue, 09 Jun 2015)

  New Revision: 50800

  http://svn.ruby-lang.org/cgi-bin/viewvc.cgi?view=revision&revision=50800

  Log:
    * lib/matrix.rb: Simplify and optimize EratosthenesSieve
      based on patch by Ajay Kumar. [Fixes GH-921]

  Modified files:
    trunk/ChangeLog
    trunk/lib/prime.rb
Index: ChangeLog
===================================================================
--- ChangeLog	(revision 50799)
+++ ChangeLog	(revision 50800)
@@ -1,3 +1,8 @@ https://github.com/ruby/ruby/blob/trunk/ChangeLog#L1
+Tue Jun  9 11:45:00 2015  Marc-Andre Lafortune  <ruby-core@m...>
+
+	* lib/matrix.rb: Simplify and optimize EratosthenesSieve
+	  based on patch by Ajay Kumar. [Fixes GH-921]
+
 Mon Jun  8 05:09:58 2015  Koichi Sasada  <ko1@a...>
 
 	* gc.c (obj_info): print method id for T_IMEMO/ment.
Index: lib/prime.rb
===================================================================
--- lib/prime.rb	(revision 50799)
+++ lib/prime.rb	(revision 50800)
@@ -425,13 +425,10 @@ class Prime https://github.com/ruby/ruby/blob/trunk/lib/prime.rb#L425
       root = Integer(Math.sqrt(segment_max).floor)
 
       sieving_primes = @primes[1 .. -1].take_while { |prime| prime <= root }
-      offsets = Array.new(sieving_primes.size) do |i|
-        (-(segment_min + 1 + sieving_primes[i]) / 2) % sieving_primes[i]
-      end
 
       segment = ((segment_min + 1) .. segment_max).step(2).to_a
-      sieving_primes.each_with_index do |prime, index|
-        composite_index = offsets[index]
+      sieving_primes.each do |prime|
+        composite_index = (-(segment_min + 1 + prime) / 2) % prime
         while composite_index < segment.size do
           segment[composite_index] = nil
           composite_index += prime

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