numeric.c: round to nearest even

* numeric.c (flo_round, int_round): support round-to-nearest-even
  semantics of IEEE 754 to match sprintf behavior, and add `half:`
  optional keyword argument for the old behavior.
  [ruby-core:76273] [Bug #12548]

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@56590 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

1 files changed, 46 insertions, 4 deletions

diff --git a/test/test_mathn.rb b/test/test_mathn.rb
index aaf132ba88..2ea049502c 100644
--- a/test/test_mathn.rb
+++ b/test/test_mathn.rb
@@ -96,17 +96,17 @@ class TestMathn < Test::Unit::TestCase
   def test_round
     assert_separately(%w[-rmathn], <<-EOS, ignore_stderr: true)
       assert_equal( 3, ( 13/5).round)
-      assert_equal( 3, (  5/2).round)
+      assert_equal( 2, (  5/2).round)
       assert_equal( 2, ( 12/5).round)
       assert_equal(-2, (-12/5).round)
-      assert_equal(-3, ( -5/2).round)
+      assert_equal(-2, ( -5/2).round)
       assert_equal(-3, (-13/5).round)
 
       assert_equal( 3, ( 13/5).round(0))
-      assert_equal( 3, (  5/2).round(0))
+      assert_equal( 2, (  5/2).round(0))
       assert_equal( 2, ( 12/5).round(0))
       assert_equal(-2, (-12/5).round(0))
-      assert_equal(-3, ( -5/2).round(0))
+      assert_equal(-2, ( -5/2).round(0))
       assert_equal(-3, (-13/5).round(0))
 
       assert_equal(( 13/5), ( 13/5).round(2))
@@ -115,6 +115,48 @@ class TestMathn < Test::Unit::TestCase
       assert_equal((-12/5), (-12/5).round(2))
       assert_equal(( -5/2), ( -5/2).round(2))
       assert_equal((-13/5), (-13/5).round(2))
+
+      assert_equal( 3, ( 13/5).round(half: :even))
+      assert_equal( 2, (  5/2).round(half: :even))
+      assert_equal( 2, ( 12/5).round(half: :even))
+      assert_equal(-2, (-12/5).round(half: :even))
+      assert_equal(-2, ( -5/2).round(half: :even))
+      assert_equal(-3, (-13/5).round(half: :even))
+
+      assert_equal( 3, ( 13/5).round(0, half: :even))
+      assert_equal( 2, (  5/2).round(0, half: :even))
+      assert_equal( 2, ( 12/5).round(0, half: :even))
+      assert_equal(-2, (-12/5).round(0, half: :even))
+      assert_equal(-2, ( -5/2).round(0, half: :even))
+      assert_equal(-3, (-13/5).round(0, half: :even))
+
+      assert_equal(( 13/5), ( 13/5).round(2, half: :even))
+      assert_equal((  5/2), (  5/2).round(2, half: :even))
+      assert_equal(( 12/5), ( 12/5).round(2, half: :even))
+      assert_equal((-12/5), (-12/5).round(2, half: :even))
+      assert_equal(( -5/2), ( -5/2).round(2, half: :even))
+      assert_equal((-13/5), (-13/5).round(2, half: :even))
+
+      assert_equal( 3, ( 13/5).round(half: :up))
+      assert_equal( 3, (  5/2).round(half: :up))
+      assert_equal( 2, ( 12/5).round(half: :up))
+      assert_equal(-2, (-12/5).round(half: :up))
+      assert_equal(-3, ( -5/2).round(half: :up))
+      assert_equal(-3, (-13/5).round(half: :up))
+
+      assert_equal( 3, ( 13/5).round(0, half: :up))
+      assert_equal( 3, (  5/2).round(0, half: :up))
+      assert_equal( 2, ( 12/5).round(0, half: :up))
+      assert_equal(-2, (-12/5).round(0, half: :up))
+      assert_equal(-3, ( -5/2).round(0, half: :up))
+      assert_equal(-3, (-13/5).round(0, half: :up))
+
+      assert_equal(( 13/5), ( 13/5).round(2, half: :up))
+      assert_equal((  5/2), (  5/2).round(2, half: :up))
+      assert_equal(( 12/5), ( 12/5).round(2, half: :up))
+      assert_equal((-12/5), (-12/5).round(2, half: :up))
+      assert_equal(( -5/2), ( -5/2).round(2, half: :up))
+      assert_equal((-13/5), (-13/5).round(2, half: :up))
     EOS
   end
 end