bigdecimal.c: check underflow

* ext/bigdecimal/bigdecimal.c (BigDecimal_to_f): check underflow since
  strtod() sets errno to ERANGE at underflow too.  [ruby-core:47342]
  [Bug #6944]

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@36854 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

3 files changed, 36 insertions, 8 deletions

diff --git a/ChangeLog b/ChangeLog
index 55b791bf66..1d396d38f6 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,9 @@
+Thu Aug 30 16:17:52 2012  Nobuyoshi Nakada  <nobu@ruby-lang.org>
+
+	* ext/bigdecimal/bigdecimal.c (BigDecimal_to_f): check underflow since
+	  strtod() sets errno to ERANGE at underflow too.  [ruby-core:47342]
+	  [Bug #6944]
+
 Thu Aug 30 12:44:43 2012  Akinori MUSHA  <knu@iDaemons.org>
 
 	* lib/set.rb (Set#{<,>,<=,>=}): Define comparison operators as
diff --git a/ext/bigdecimal/bigdecimal.c b/ext/bigdecimal/bigdecimal.c
index 866ce345fc..e8ba40a531 100644
--- a/ext/bigdecimal/bigdecimal.c
+++ b/ext/bigdecimal/bigdecimal.c
@@ -696,8 +696,10 @@ BigDecimal_to_f(VALUE self)
     VpToString(p, buf, 0, 0);
     errno = 0;
     d = strtod(buf, 0);
-    if (errno == ERANGE)
-	goto overflow;
+    if (errno == ERANGE) {
+	if (d == 0.0) goto underflow;
+	if (fabs(d) >= HUGE_VAL) goto overflow;
+    }
     return rb_float_new(d);
 
 overflow:
diff --git a/test/bigdecimal/test_bigdecimal.rb b/test/bigdecimal/test_bigdecimal.rb
index d440e4cedb..6694697e0e 100644
--- a/test/bigdecimal/test_bigdecimal.rb
+++ b/test/bigdecimal/test_bigdecimal.rb
@@ -540,15 +540,35 @@ class TestBigDecimal < Test::Unit::TestCase
     assert_kind_of(Float,   x .to_f)
     assert_kind_of(Float, (-x).to_f)
 
+    bug6944 = '[ruby-core:47342]'
+
     BigDecimal.mode(BigDecimal::EXCEPTION_UNDERFLOW, true)
-    assert_raise(FloatDomainError) {
-      BigDecimal("1e#{Float::MIN_10_EXP - 2*Float::DIG}").to_f }
-    assert_raise(FloatDomainError) {
-      BigDecimal("-1e#{Float::MIN_10_EXP - 2*Float::DIG}").to_f }
+    x = "1e#{Float::MIN_10_EXP - 2*Float::DIG}"
+    assert_raise(FloatDomainError, x) {BigDecimal(x).to_f}
+    x = "-#{x}"
+    assert_raise(FloatDomainError, x) {BigDecimal(x).to_f}
+    x = "1e#{Float::MIN_10_EXP - Float::DIG}"
+    assert_nothing_raised(FloatDomainError, x) {
+      assert_in_delta(0.0, BigDecimal(x).to_f, 10**Float::MIN_10_EXP, bug6944)
+    }
+    x = "-#{x}"
+    assert_nothing_raised(FloatDomainError, x) {
+      assert_in_delta(0.0, BigDecimal(x).to_f, 10**Float::MIN_10_EXP, bug6944)
+    }
 
     BigDecimal.mode(BigDecimal::EXCEPTION_UNDERFLOW, false)
-    assert_equal( 0.0, BigDecimal("1e#{Float::MIN_10_EXP - 2*Float::DIG}").to_f)
-    assert_equal(-0.0, BigDecimal("-1e#{Float::MIN_10_EXP - 2*Float::DIG}").to_f)
+    x = "1e#{Float::MIN_10_EXP - 2*Float::DIG}"
+    assert_equal( 0.0, BigDecimal(x).to_f, x)
+    x = "-#{x}"
+    assert_equal(-0.0, BigDecimal(x).to_f, x)
+    x = "1e#{Float::MIN_10_EXP - Float::DIG}"
+    assert_nothing_raised(FloatDomainError, x) {
+      assert_in_delta(0.0, BigDecimal(x).to_f, 10**Float::MIN_10_EXP, bug6944)
+    }
+    x = "-#{x}"
+    assert_nothing_raised(FloatDomainError, x) {
+      assert_in_delta(0.0, BigDecimal(x).to_f, 10**Float::MIN_10_EXP, bug6944)
+    }
   end
 
   def test_coerce