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

4 files changed, 141 insertions, 18 deletions

diff --git a/test/ruby/test_float.rb b/test/ruby/test_float.rb
index b31c0415f2..f2989e4f5b 100644
--- a/test/ruby/test_float.rb
+++ b/test/ruby/test_float.rb
@@ -659,6 +659,48 @@ class TestFloat < Test::Unit::TestCase
     }
   end
 
+  def test_round_half_even
+    assert_equal(12.0, 12.5.round(half: :even))
+    assert_equal(14.0, 13.5.round(half: :even))
+
+    assert_equal(2.2, 2.15.round(1, half: :even))
+    assert_equal(2.2, 2.25.round(1, half: :even))
+    assert_equal(2.4, 2.35.round(1, half: :even))
+
+    assert_equal(-2.2, -2.15.round(1, half: :even))
+    assert_equal(-2.2, -2.25.round(1, half: :even))
+    assert_equal(-2.4, -2.35.round(1, half: :even))
+
+    assert_equal(7.1364, 7.13645.round(4, half: :even))
+    assert_equal(7.1365, 7.1364501.round(4, half: :even))
+    assert_equal(7.1364, 7.1364499.round(4, half: :even))
+
+    assert_equal(-7.1364, -7.13645.round(4, half: :even))
+    assert_equal(-7.1365, -7.1364501.round(4, half: :even))
+    assert_equal(-7.1364, -7.1364499.round(4, half: :even))
+  end
+
+  def test_round_half_up
+    assert_equal(13.0, 12.5.round(half: :up))
+    assert_equal(14.0, 13.5.round(half: :up))
+
+    assert_equal(2.2, 2.15.round(1, half: :up))
+    assert_equal(2.3, 2.25.round(1, half: :up))
+    assert_equal(2.4, 2.35.round(1, half: :up))
+
+    assert_equal(-2.2, -2.15.round(1, half: :up))
+    assert_equal(-2.3, -2.25.round(1, half: :up))
+    assert_equal(-2.4, -2.35.round(1, half: :up))
+
+    assert_equal(7.1365, 7.13645.round(4, half: :up))
+    assert_equal(7.1365, 7.1364501.round(4, half: :up))
+    assert_equal(7.1364, 7.1364499.round(4, half: :up))
+
+    assert_equal(-7.1365, -7.13645.round(4, half: :up))
+    assert_equal(-7.1365, -7.1364501.round(4, half: :up))
+    assert_equal(-7.1364, -7.1364499.round(4, half: :up))
+  end
+
   def test_Float
     assert_in_delta(0.125, Float("0.1_2_5"), 0.00001)
     assert_in_delta(0.125, "0.1_2_5__".to_f, 0.00001)
diff --git a/test/ruby/test_integer.rb b/test/ruby/test_integer.rb
index 6e505ec003..d9dd754ca6 100644
--- a/test/ruby/test_integer.rb
+++ b/test/ruby/test_integer.rb
@@ -187,13 +187,49 @@ class TestInteger < Test::Unit::TestCase
     assert_int_equal(11110, 11111.round(-1))
     assert_int_equal(11100, 11111.round(-2))
     assert_int_equal(+200, +249.round(-2))
-    assert_int_equal(+300, +250.round(-2))
+    assert_int_equal(+200, +250.round(-2))
     assert_int_equal(-200, -249.round(-2))
-    assert_int_equal(-300, -250.round(-2))
-    assert_int_equal(+30 * 10**70, (+25 * 10**70).round(-71))
-    assert_int_equal(-30 * 10**70, (-25 * 10**70).round(-71))
+    assert_int_equal(+200, +249.round(-2, half: :even))
+    assert_int_equal(+200, +250.round(-2, half: :even))
+    assert_int_equal(+300, +349.round(-2, half: :even))
+    assert_int_equal(+400, +350.round(-2, half: :even))
+    assert_int_equal(+200, +249.round(-2, half: :up))
+    assert_int_equal(+300, +250.round(-2, half: :up))
+    assert_int_equal(+300, +349.round(-2, half: :up))
+    assert_int_equal(+400, +350.round(-2, half: :up))
+    assert_int_equal(-200, -250.round(-2))
+    assert_int_equal(-200, -249.round(-2, half: :even))
+    assert_int_equal(-200, -250.round(-2, half: :even))
+    assert_int_equal(-300, -349.round(-2, half: :even))
+    assert_int_equal(-400, -350.round(-2, half: :even))
+    assert_int_equal(-200, -249.round(-2, half: :up))
+    assert_int_equal(-300, -250.round(-2, half: :up))
+    assert_int_equal(-300, -349.round(-2, half: :up))
+    assert_int_equal(-400, -350.round(-2, half: :up))
+    assert_int_equal(+20 * 10**70, (+25 * 10**70).round(-71))
+    assert_int_equal(-20 * 10**70, (-25 * 10**70).round(-71))
     assert_int_equal(+20 * 10**70, (+25 * 10**70 - 1).round(-71))
     assert_int_equal(-20 * 10**70, (-25 * 10**70 + 1).round(-71))
+    assert_int_equal(+40 * 10**70, (+35 * 10**70).round(-71))
+    assert_int_equal(-40 * 10**70, (-35 * 10**70).round(-71))
+    assert_int_equal(+30 * 10**70, (+35 * 10**70 - 1).round(-71))
+    assert_int_equal(-30 * 10**70, (-35 * 10**70 + 1).round(-71))
+    assert_int_equal(+20 * 10**70, (+25 * 10**70).round(-71, half: :even))
+    assert_int_equal(-20 * 10**70, (-25 * 10**70).round(-71, half: :even))
+    assert_int_equal(+20 * 10**70, (+25 * 10**70 - 1).round(-71, half: :even))
+    assert_int_equal(-20 * 10**70, (-25 * 10**70 + 1).round(-71, half: :even))
+    assert_int_equal(+40 * 10**70, (+35 * 10**70).round(-71, half: :even))
+    assert_int_equal(-40 * 10**70, (-35 * 10**70).round(-71, half: :even))
+    assert_int_equal(+30 * 10**70, (+35 * 10**70 - 1).round(-71, half: :even))
+    assert_int_equal(-30 * 10**70, (-35 * 10**70 + 1).round(-71, half: :even))
+    assert_int_equal(+30 * 10**70, (+25 * 10**70).round(-71, half: :up))
+    assert_int_equal(-30 * 10**70, (-25 * 10**70).round(-71, half: :up))
+    assert_int_equal(+20 * 10**70, (+25 * 10**70 - 1).round(-71, half: :up))
+    assert_int_equal(-20 * 10**70, (-25 * 10**70 + 1).round(-71, half: :up))
+    assert_int_equal(+40 * 10**70, (+35 * 10**70).round(-71, half: :up))
+    assert_int_equal(-40 * 10**70, (-35 * 10**70).round(-71, half: :up))
+    assert_int_equal(+30 * 10**70, (+35 * 10**70 - 1).round(-71, half: :up))
+    assert_int_equal(-30 * 10**70, (-35 * 10**70 + 1).round(-71, half: :up))
 
     assert_int_equal(1111_1111_1111_1111_1111_1111_1111_1110, 1111_1111_1111_1111_1111_1111_1111_1111.round(-1))
     assert_int_equal(-1111_1111_1111_1111_1111_1111_1111_1110, (-1111_1111_1111_1111_1111_1111_1111_1111).round(-1))
diff --git a/test/ruby/test_rational.rb b/test/ruby/test_rational.rb
index 387f4121cf..d65c292970 100644
--- a/test/ruby/test_rational.rb
+++ b/test/ruby/test_rational.rb
@@ -597,17 +597,20 @@ class Rational_Test < Test::Unit::TestCase
   end
 
   def test_trunc
-    [[Rational(13, 5),  [ 2,  3,  2,  3]], #  2.6
-     [Rational(5, 2),   [ 2,  3,  2,  3]], #  2.5
-     [Rational(12, 5),  [ 2,  3,  2,  2]], #  2.4
-     [Rational(-12,5),  [-3, -2, -2, -2]], # -2.4
-     [Rational(-5, 2),  [-3, -2, -2, -3]], # -2.5
-     [Rational(-13, 5), [-3, -2, -2, -3]], # -2.6
+    [[Rational(13, 5),  [ 2,  3,  2,  3,  3,  3]], #  2.6
+     [Rational(5, 2),   [ 2,  3,  2,  2,  2,  3]], #  2.5
+     [Rational(12, 5),  [ 2,  3,  2,  2,  2,  2]], #  2.4
+     [Rational(-12,5),  [-3, -2, -2, -2, -2, -2]], # -2.4
+     [Rational(-5, 2),  [-3, -2, -2, -2, -2, -3]], # -2.5
+     [Rational(-13, 5), [-3, -2, -2, -3, -3, -3]], # -2.6
     ].each do |i, a|
-      assert_equal(a[0], i.floor)
-      assert_equal(a[1], i.ceil)
-      assert_equal(a[2], i.truncate)
-      assert_equal(a[3], i.round)
+      s = proc {i.inspect}
+      assert_equal(a[0], i.floor, s)
+      assert_equal(a[1], i.ceil, s)
+      assert_equal(a[2], i.truncate, s)
+      assert_equal(a[3], i.round, s)
+      assert_equal(a[4], i.round(half: :even), s)
+      assert_equal(a[5], i.round(half: :up), s)
     end
   end
 
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