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!).

diff --git a/Lib/test/test_float.py b/Lib/test/test_float.py
index fb47db8eb087adb749e3176b89cda197cf437325..d616ad9543dc7ad71f3ef324834d010b396e2b92 100644 (file)
--- 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 fa090846692867ff442a2b52f9899fe55617fab2..5aeabd9d93fa9cdec81253eeac711338186bcd37 100644 (file)
--- 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);