bpo-29602: fix signed zero handling in complex constructor (#204)

* bpo-29602: fix signed zero handling in complex constructor

* Add missing have_getformat definition; remove use of unittest subtests.
diff --git a/Lib/test/test_complex.py b/Lib/test/test_complex.py
index c0383b2..02b292f 100644
--- a/Lib/test/test_complex.py
+++ b/Lib/test/test_complex.py
@@ -8,6 +8,13 @@
 NAN = float("nan")
 # These tests ensure that complex math does the right thing
 
+# decorator for skipping tests on non-IEEE 754 platforms
+have_getformat = hasattr(float, "__getformat__")
+requires_IEEE_754 = unittest.skipUnless(have_getformat and
+    float.__getformat__("double").startswith("IEEE"),
+    "test requires IEEE 754 doubles")
+
+
 class ComplexTest(unittest.TestCase):
 
     def assertAlmostEqual(self, a, b):
@@ -441,6 +448,28 @@
                     b = 'y %s x' % op
                     self.assertTrue(type(eval(a)) is type(eval(b)) is xcomplex)
 
+    @requires_IEEE_754
+    def test_constructor_special_numbers(self):
+        class complex2(complex):
+            pass
+        for x in 0.0, -0.0, INF, -INF, NAN:
+            for y in 0.0, -0.0, INF, -INF, NAN:
+                z = complex(x, y)
+                self.assertFloatsAreIdentical(z.real, x)
+                self.assertFloatsAreIdentical(z.imag, y)
+                z = complex2(x, y)
+                self.assertIs(type(z), complex2)
+                self.assertFloatsAreIdentical(z.real, x)
+                self.assertFloatsAreIdentical(z.imag, y)
+                z = complex(complex2(x, y))
+                self.assertIs(type(z), complex)
+                self.assertFloatsAreIdentical(z.real, x)
+                self.assertFloatsAreIdentical(z.imag, y)
+                z = complex2(complex(x, y))
+                self.assertIs(type(z), complex2)
+                self.assertFloatsAreIdentical(z.real, x)
+                self.assertFloatsAreIdentical(z.imag, y)
+
     def test_hash(self):
         for x in xrange(-30, 30):
             self.assertEqual(hash(x), hash(complex(x, 0)))