Merge latest dtoa.c [Bug #13545]

Apply some part of http://www.netlib.org/fp/dtoa.c with my eyes...

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@58796 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

2 files changed, 9 insertions, 5 deletions

diff --git a/test/ruby/test_float.rb b/test/ruby/test_float.rb
index 579b1d186a..17e831812e 100644
--- a/test/ruby/test_float.rb
+++ b/test/ruby/test_float.rb
@@ -16,6 +16,8 @@ class TestFloat < Test::Unit::TestCase
     assert_in_delta(13.4 % 1, 0.4, 0.0001)
     assert_equal(36893488147419111424,
                  36893488147419107329.0.to_i)
+    assert_equal(1185151044158398820374743613440,
+                 1.1851510441583988e+30.to_i)
   end
 
   def nan_test(x,y)
diff --git a/util.c b/util.c
index f5ad0ec810..3ebb2fea9a 100644
--- a/util.c
+++ b/util.c
@@ -2117,7 +2117,7 @@ break2:
     for (nd = nf = 0; (c = *s) >= '0' && c <= '9'; nd++, s++)
         if (nd < 9)
             y = 10*y + c - '0';
-        else if (nd < 16)
+        else if (nd < DBL_DIG + 2)
             z = 10*z + c - '0';
     nd0 = nd;
 #ifdef USE_LOCALE
@@ -2157,17 +2157,19 @@ break2:
         for (; c >= '0' && c <= '9'; c = *++s) {
 have_dig:
             nz++;
-            if (nd > DBL_DIG * 4) continue;
+            if (nd > DBL_DIG * 4) {
+		continue;
+	    }
             if (c -= '0') {
                 nf += nz;
                 for (i = 1; i < nz; i++)
                     if (nd++ < 9)
                         y *= 10;
-                    else if (nd <= DBL_DIG + 1)
+                    else if (nd <= DBL_DIG + 2)
                         z *= 10;
                 if (nd++ < 9)
                     y = 10*y + c;
-                else if (nd <= DBL_DIG + 1)
+                else if (nd <= DBL_DIG + 2)
                     z = 10*z + c;
                 nz = 0;
             }
@@ -2255,7 +2257,7 @@ ret0:
 
     if (!nd0)
         nd0 = nd;
-    k = nd < DBL_DIG + 1 ? nd : DBL_DIG + 1;
+    k = nd < DBL_DIG + 2 ? nd : DBL_DIG + 2;
     dval(rv) = y;
     if (k > 9) {
 #ifdef SET_INEXACT