bigdecimal.c: more precision

* ext/bigdecimal/bigdecimal.c (BigDecimal_div2): need more room
  for precision to round.  [ruby-core:77475] [Bug #12805]

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@56336 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

ChangeLog

@@ -1,3 +1,8 @@
+Tue Oct  4 09:55:12 2016  Nobuyoshi Nakada  <nobu@ruby-lang.org>
+
+	* ext/bigdecimal/bigdecimal.c (BigDecimal_div2): need more room
+	  for precision to round.  [ruby-core:77475] [Bug #12805]
+
 Tue Oct  4 06:05:46 2016  NARUSE, Yui  <naruse@ruby-lang.org>
 
 	* regcomp.c (onig_print_compiled_byte_code): make the shown address

ext/bigdecimal/bigdecimal.c

@@ -1533,7 +1533,7 @@ BigDecimal_div2(VALUE self, VALUE b, VALUE n)
         size_t mx = ix + VpBaseFig()*2;
         size_t pl = VpSetPrecLimit(0);
 
-        GUARD_OBJ(cv, VpCreateRbObject(mx, "0"));
+        GUARD_OBJ(cv, VpCreateRbObject(mx + VpBaseFig(), "0"));
         GUARD_OBJ(av, GetVpValue(self, 1));
         GUARD_OBJ(bv, GetVpValue(b, 1));
         mx = av->Prec + bv->Prec + 2;

test/bigdecimal/test_bigdecimal.rb

@@ -807,6 +807,12 @@ class TestBigDecimal < Test::Unit::TestCase
       BigDecimal.mode(BigDecimal::EXCEPTION_INFINITY, false)
       assert_equal(0, BigDecimal("0").div(BigDecimal("Infinity")))
     end
+
+    x = BigDecimal.new("1")
+    y = BigDecimal.new("0.22")
+    (2..20).each do |i|
+      assert_equal ("0."+"45"*(i/2)+"5"*(i%2)+"E1"), x.div(y, i).to_s, "#{i}"
+    end
   end
 
   def test_abs_bigdecimal