util.c: do not underflow

* util.c (ruby_strtod): do not underflow only by preceeding zeros,
  which may be canceled out by the exponent.
  http://twitter.com/kazuho/status/753829998767714305

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@55689 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

3 files changed, 8 insertions, 1 deletions

diff --git a/ChangeLog b/ChangeLog
index 1313d5c71a..fdade505fc 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,9 @@
+Fri Jul 15 17:08:57 2016  Nobuyoshi Nakada  <nobu@ruby-lang.org>
+
+	* util.c (ruby_strtod): do not underflow only by preceeding zeros,
+	  which may be canceled out by the exponent.
+	  http://twitter.com/kazuho/status/753829998767714305
+
 Fri Jul 15 15:32:13 2016  NAKAMURA Usaku  <usa@ruby-lang.org>
 
 	* time.c (time_arg): it seems that this function sometimes causes SEGV
diff --git a/test/ruby/test_literal.rb b/test/ruby/test_literal.rb
index c37b206539..05b81f944d 100644
--- a/test/ruby/test_literal.rb
+++ b/test/ruby/test_literal.rb
@@ -493,6 +493,7 @@ class TestRubyLiteral < Test::Unit::TestCase
         }
       }
     }
+    assert_equal(100.0, 0.0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000100e100)
   end
 
   def test_symbol_list
diff --git a/util.c b/util.c
index 0b0c935832..17819e522a 100644
--- a/util.c
+++ b/util.c
@@ -2145,7 +2145,7 @@ break2:
         for (; c >= '0' && c <= '9'; c = *++s) {
 have_dig:
             nz++;
-            if (nf > DBL_DIG * 4) continue;
+            if (nd > DBL_DIG * 4) continue;
             if (c -= '0') {
                 nf += nz;
                 for (i = 1; i < nz; i++)