Update to ruby/spec@254c380

1 files changed, 9 insertions, 0 deletions

diff --git a/spec/ruby/core/enumerable/sum_spec.rb b/spec/ruby/core/enumerable/sum_spec.rb
index c9d7017b45..4a978794e5 100644
--- a/spec/ruby/core/enumerable/sum_spec.rb
+++ b/spec/ruby/core/enumerable/sum_spec.rb
@@ -25,4 +25,13 @@ describe 'Enumerable#sum' do
   it 'takes a block to transform the elements' do
     @enum.sum { |element| element * 2 }.should == 10/3r
   end
+
+  # https://bugs.ruby-lang.org/issues/12217
+  # https://github.com/ruby/ruby/blob/master/doc/ChangeLog-2.4.0#L6208-L6214
+  it "uses Kahan's compensated summation algorithm for precise sum of float numbers" do
+    floats = [2.7800000000000002, 5.0, 2.5, 4.44, 3.89, 3.89, 4.44, 7.78, 5.0, 2.7800000000000002, 5.0, 2.5].to_enum
+    naive_sum = floats.reduce { |sum, e| sum + e }
+    naive_sum.should == 50.00000000000001
+    floats.sum.should == 50.0
+  end
 end