Fix Math.cbrt(0.0) on glibc

This should return 0, but on glibc it returned NaN.

Fixes [Bug #17804]

2 files changed, 2 insertions, 1 deletions

diff --git a/math.c b/math.c
index 470979c424..3b72149feb 100644
--- a/math.c
+++ b/math.c
@@ -703,7 +703,7 @@ math_cbrt(VALUE unused_obj, VALUE x)
     double f = Get_Double(x);
     double r = cbrt(f);
 #if defined __GLIBC__
-    if (isfinite(r)) {
+    if (isfinite(r) && !(f == 0.0 && r == 0.0)) {
 	r = (2.0 * r + (f / r / r)) / 3.0;
     }
 #endif
diff --git a/test/ruby/test_math.rb b/test/ruby/test_math.rb
index 5cc12bcfeb..6c2b25787f 100644
--- a/test/ruby/test_math.rb
+++ b/test/ruby/test_math.rb
@@ -201,6 +201,7 @@ class TestMath < Test::Unit::TestCase
     check(-2, Math.cbrt(-8))
     check(3, Math.cbrt(27))
     check(-0.1, Math.cbrt(-0.001))
+    check(0.0, Math.cbrt(0.0))
     assert_nothing_raised { assert_infinity(Math.cbrt(1.0/0)) }
     assert_operator(Math.cbrt(1.0 - Float::EPSILON), :<=, 1.0)
   end