rss.rb: fix usec width

* lib/rss/rss.rb (Time#w3cdtf): fix zero-trimmed width of fraction
  digits.  [ruby-core:70667] [Bug #11509]

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@51766 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

ChangeLog

@@ -1,3 +1,8 @@
+Sat Sep  5 11:39:52 2015  Nobuyoshi Nakada  <nobu@ruby-lang.org>
+
+	* lib/rss/rss.rb (Time#w3cdtf): fix zero-trimmed width of fraction
+	  digits.  [ruby-core:70667] [Bug #11509]
+
 Sat Sep  5 08:28:58 2015  Nobuyoshi Nakada  <nobu@ruby-lang.org>
 
 	* hash.c (rb_hash_equal, rb_hash_eql): [DOC] the orders of each

lib/rss/rss.rb

@@ -53,7 +53,7 @@ class Time
       if usec.zero?
         fraction_digits = 0
       else
-        fraction_digits = Math.log10(usec.to_s.sub(/0*$/, '').to_i).floor + 1
+        fraction_digits = strftime('%6N').sub!(/0*\z/, '').size
       end
       xmlschema(fraction_digits)
     end

test/rss/test_to_s.rb

@@ -102,6 +102,12 @@ module RSS
       assert_textinput20(@textinput_info, rss.textinput)
     end
 
+    def test_time_w3cdtf
+      assert_equal("2015-09-05T01:25:48.0001Z",
+                   Time.utc(2015, 9, 5, 1, 25, 48, 100).w3cdtf,
+                   '[ruby-core:70667] [Bug #11509]')
+    end
+
     private
     def setup_xml_declaration_info
       @version = "1.0"