merge revision(s) 55604,55612: [Backport #13138]

	* numeric.c (flo_round): [EXPERIMENTAL] adjust the case that the
	  receiver is close to the exact but unrepresentable middle value
	  of two values in the given precision.
	  http://d.hatena.ne.jp/hnw/20160702

	numeric.c: round as double

	* numeric.c (flo_round): compare as double, not long double with
	  i387.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/branches/ruby_2_3@58513 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

1 files changed, 9 insertions, 3 deletions

diff --git a/numeric.c b/numeric.c
index ca961d8d6c..c1c673927c 100644
--- a/numeric.c
+++ b/numeric.c
@@ -1786,7 +1786,7 @@ static VALUE
 flo_round(int argc, VALUE *argv, VALUE num)
 {
     VALUE nd;
-    double number, f;
+    double number, f, x;
     int ndigits = 0;
     int binexp;
     enum {float_dig = DBL_DIG+2};
@@ -1828,8 +1828,14 @@ flo_round(int argc, VALUE *argv, VALUE num)
 	return DBL2NUM(0);
     }
     f = pow(10, ndigits);
-    return DBL2NUM(round(number * f) / f);
-}
+    x = round(number * f);
+    if (x > 0) {
+	if ((double)((x + 0.5) / f) <= number) x += 1;
+    }
+    else {
+	if ((double)((x - 0.5) / f) >= number) x -= 1;
+    }
+    return DBL2NUM(x / f);}
 
 /*
  *  call-seq: