x**2 should about equal x*x (including for a float x such that the result is

inf) but didn't; added a test to test_float to verify that, and ignored the
ERANGE value for errno in the pow operation to make the new test pass (with
help from Marilyn Davis at the Google Python Sprint -- thanks!).

2 files changed, 17 insertions, 4 deletions

diff --git a/Lib/test/test_float.py b/Lib/test/test_float.py
index fb47db8eb0..d616ad9543 100644
--- a/Lib/test/test_float.py
+++ b/Lib/test/test_float.py
@@ -99,12 +99,25 @@ class IEEEFormatTestCase(unittest.TestCase):
                               ('<f', LE_FLOAT_NAN)]:
                 struct.unpack(fmt, data)
 
+# on an IEEE platform, "overflowing" operations produce infinity
+
+class IEEEOperationsTestCase(unittest.TestCase):
+    if float.__getformat__("double").startswith("IEEE"):
+        def test_double_infinity(self):
+            big = 4.8e159
+            pro = big*big
+            self.assertEquals(repr(pro), 'inf')
+            sqr = big**2
+            self.assertEquals(repr(sqr), 'inf')
+
 
 def test_main():
     test_support.run_unittest(
         FormatFunctionsTestCase,
         UnknownFormatTestCase,
-        IEEEFormatTestCase)
+        IEEEFormatTestCase,
+        IEEEOperationsTestCase,
+        )
 
 if __name__ == '__main__':
     test_main()
diff --git a/Objects/floatobject.c b/Objects/floatobject.c
index fa09084669..5aeabd9d93 100644
--- a/Objects/floatobject.c
+++ b/Objects/floatobject.c
@@ -821,12 +821,12 @@ float_pow(PyObject *v, PyObject *w, PyObject *z)
 	ix = pow(iv, iw);
 	PyFPE_END_PROTECT(ix)
 	Py_ADJUST_ERANGE1(ix);
-	if (errno != 0) {
+        /* we need to ignore ERANGE here and just return inf */
+	if (errno != 0 && errno != ERANGE) {
 		/* We don't expect any errno value other than ERANGE, but
 		 * the range of libm bugs appears unbounded.
 		 */
-		PyErr_SetFromErrno(errno == ERANGE ? PyExc_OverflowError :
-						     PyExc_ValueError);
+		PyErr_SetFromErrno(PyExc_ValueError);
 		return NULL;
 	}
 	return PyFloat_FromDouble(ix);