Index: Lib/test/test_float.py =================================================================== --- Lib/test/test_float.py (revision 76881) +++ Lib/test/test_float.py (working copy) @@ -12,6 +12,11 @@ INF = float("inf") NAN = float("nan") +# decorator for skipping tests on non-IEEE 754 platforms +requires_IEEE_754 = unittest.skipUnless( + float.__getformat__("double").startswith("IEEE"), + "test requires IEEE 754 doubles") + #locate file with float format test values test_dir = os.path.dirname(__file__) or os.curdir format_testfile = os.path.join(test_dir, 'formatfloat_testcases.txt') @@ -142,6 +147,143 @@ self.assertRaises(OverflowError, float('-inf').as_integer_ratio) self.assertRaises(ValueError, float('nan').as_integer_ratio) + def assertEqualAndEqualSign(self, a, b): + self.assertEqual((a, copysign(1.0, a)), (b, copysign(1.0, b))) + + @requires_IEEE_754 + def test_float_pow(self): + # test builtin pow and ** operator for IEEE 754 special cases. + # Special cases taken from section F.9.4.4 of the C99 specification + + for pow_op in (pow, operator.pow): + + # (+-0)**y raises ZeroDivisionError for y a negative odd integer + self.assertRaises(ZeroDivisionError, pow_op, -0.0, -1.0) + self.assertRaises(ZeroDivisionError, pow_op, 0.0, -1.0) + + # (+-0)**y raises ZeroDivisionError for y negative, not an odd integer + self.assertRaises(ZeroDivisionError, pow_op, -0.0, -2.0) + self.assertRaises(ZeroDivisionError, pow_op, -0.0, -0.5) + self.assertRaises(ZeroDivisionError, pow_op, 0.0, -2.0) + self.assertRaises(ZeroDivisionError, pow_op, 0.0, -0.5) + + # (+-0)**y is +-0, for y a positive odd integer + self.assertEqualAndEqualSign(pow_op(-0.0, 1.0), -0.0) + self.assertEqualAndEqualSign(pow_op(0.0, 1.0), 0.0) + + # (+-0)**y is 0 for y positive, not an odd integer + self.assertEqualAndEqualSign(pow_op(-0.0, 0.5), 0.0) + self.assertEqualAndEqualSign(pow_op(-0.0, 2.0), 0.0) + self.assertEqualAndEqualSign(pow_op(0.0, 0.5), 0.0) + self.assertEqualAndEqualSign(pow_op(0.0, 2.0), 0.0) + + # -1**+-inf -> 1 + self.assertEqualAndEqualSign(pow_op(-1.0, -INF), 1.0) + self.assertEqualAndEqualSign(pow_op(-1.0, INF), 1.0) + + # 1**y = 1 for any y + self.assertEqualAndEqualSign(pow_op(1.0, -INF), 1.0) + self.assertEqualAndEqualSign(pow_op(1.0, -2.0), 1.0) + self.assertEqualAndEqualSign(pow_op(1.0, -1.0), 1.0) + self.assertEqualAndEqualSign(pow_op(1.0, -0.5), 1.0) + self.assertEqualAndEqualSign(pow_op(1.0, -0.0), 1.0) + self.assertEqualAndEqualSign(pow_op(1.0, 0.0), 1.0) + self.assertEqualAndEqualSign(pow_op(1.0, 0.5), 1.0) + self.assertEqualAndEqualSign(pow_op(1.0, 1.0), 1.0) + self.assertEqualAndEqualSign(pow_op(1.0, 2.0), 1.0) + self.assertEqualAndEqualSign(pow_op(1.0, INF), 1.0) + self.assertEqualAndEqualSign(pow_op(1.0, NAN), 1.0) + + # x**+-0 = 1 for any x + self.assertEqualAndEqualSign(pow_op(-INF, 0.0), 1.0) + self.assertEqualAndEqualSign(pow_op(-2.0, 0.0), 1.0) + self.assertEqualAndEqualSign(pow_op(-1.0, 0.0), 1.0) + self.assertEqualAndEqualSign(pow_op(-0.5, 0.0), 1.0) + self.assertEqualAndEqualSign(pow_op(-0.0, 0.0), 1.0) + self.assertEqualAndEqualSign(pow_op(0.0, 0.0), 1.0) + self.assertEqualAndEqualSign(pow_op(0.5, 0.0), 1.0) + self.assertEqualAndEqualSign(pow_op(1.0, 0.0), 1.0) + self.assertEqualAndEqualSign(pow_op(2.0, 0.0), 1.0) + self.assertEqualAndEqualSign(pow_op(INF, 0.0), 1.0) + self.assertEqualAndEqualSign(pow_op(NAN, 0.0), 1.0) + self.assertEqualAndEqualSign(pow_op(-INF, -0.0), 1.0) + self.assertEqualAndEqualSign(pow_op(-2.0, -0.0), 1.0) + self.assertEqualAndEqualSign(pow_op(-1.0, -0.0), 1.0) + self.assertEqualAndEqualSign(pow_op(-0.5, -0.0), 1.0) + self.assertEqualAndEqualSign(pow_op(-0.0, -0.0), 1.0) + self.assertEqualAndEqualSign(pow_op(0.0, -0.0), 1.0) + self.assertEqualAndEqualSign(pow_op(0.5, -0.0), 1.0) + self.assertEqualAndEqualSign(pow_op(1.0, -0.0), 1.0) + self.assertEqualAndEqualSign(pow_op(2.0, -0.0), 1.0) + self.assertEqualAndEqualSign(pow_op(INF, -0.0), 1.0) + self.assertEqualAndEqualSign(pow_op(NAN, -0.0), 1.0) + + # x**y raises for negative x < and non-integral y + self.assertRaises(ValueError, pow_op, -1.0, -0.5) + self.assertRaises(ValueError, pow_op, -1.0, 0.5) + + # but shouldn't raise for integral powers of negative numbers + self.assertEqualAndEqualSign(pow_op(-1.0, -2.0), 1.0) + self.assertEqualAndEqualSign(pow_op(-1.0, -1.0), -1.0) + self.assertEqualAndEqualSign(pow_op(-1.0, -0.0), 1.0) + self.assertEqualAndEqualSign(pow_op(-1.0, 0.0), 1.0) + self.assertEqualAndEqualSign(pow_op(-1.0, 1.0), -1.0) + self.assertEqualAndEqualSign(pow_op(-1.0, 2.0), 1.0) + self.assertEqualAndEqualSign(pow_op(-2.0, -2.0), 0.25) + self.assertEqualAndEqualSign(pow_op(-2.0, -1.0), -0.5) + self.assertEqualAndEqualSign(pow_op(-2.0, -0.0), 1.0) + self.assertEqualAndEqualSign(pow_op(-2.0, 0.0), 1.0) + self.assertEqualAndEqualSign(pow_op(-2.0, 1.0), -2.0) + self.assertEqualAndEqualSign(pow_op(-2.0, 2.0), 4.0) + + # x ** -INF is INF for abs(x) < 1 + self.assertEqualAndEqualSign(pow_op(-0.5, -INF), INF) + self.assertEqualAndEqualSign(pow_op(-0.0, -INF), INF) + self.assertEqualAndEqualSign(pow_op(0.0, -INF), INF) + self.assertEqualAndEqualSign(pow_op(0.5, -INF), INF) + + # x ** -INF is 0 for abs(x) > 1 + self.assertEqualAndEqualSign(pow_op(-INF, -INF), 0.0) + self.assertEqualAndEqualSign(pow_op(-2.0, -INF), 0.0) + self.assertEqualAndEqualSign(pow_op(2.0, -INF), 0.0) + self.assertEqualAndEqualSign(pow_op(INF, -INF), 0.0) + + # x ** INF is 0 for abs(x) < 1 + self.assertEqualAndEqualSign(pow_op(-0.5, INF), 0.0) + self.assertEqualAndEqualSign(pow_op(-0.0, INF), 0.0) + self.assertEqualAndEqualSign(pow_op(0.0, INF), 0.0) + self.assertEqualAndEqualSign(pow_op(0.5, INF), 0.0) + + # x ** INF is INF for abs(x) > 1 + self.assertEqualAndEqualSign(pow_op(-INF, INF), INF) + self.assertEqualAndEqualSign(pow_op(-2.0, INF), INF) + self.assertEqualAndEqualSign(pow_op(2.0, INF), INF) + self.assertEqualAndEqualSign(pow_op(INF, INF), INF) + + # (-INF) ** y is -0.0 for y a negative odd integer + self.assertEqualAndEqualSign(pow_op(-INF, -1.0), -0.0) + + # (-INF) ** y is 0.0 for y negative, not an odd integer + self.assertEqualAndEqualSign(pow_op(-INF, -0.5), -0.0) + self.assertEqualAndEqualSign(pow_op(-INF, -2.0), -0.0) + + # (-INF) ** y is -INF for y a positive odd integer + self.assertEqualAndEqualSign(pow_op(-INF, 1.0), -INF) + + # (-INF) ** y is INF for y positive, not an odd integer + self.assertEqualAndEqualSign(pow_op(-INF, 0.5), INF) + self.assertEqualAndEqualSign(pow_op(-INF, 2.0), INF) + + # INF ** y is INF for y positive + self.assertEqualAndEqualSign(pow_op(INF, 0.5), INF) + self.assertEqualAndEqualSign(pow_op(INF, 1.0), INF) + self.assertEqualAndEqualSign(pow_op(INF, 2.0), INF) + + # INF ** y is 0.0 for y negative + self.assertEqualAndEqualSign(pow_op(INF, -2.0), 0.0) + self.assertEqualAndEqualSign(pow_op(INF, -1.0), 0.0) + self.assertEqualAndEqualSign(pow_op(INF, -0.5), 0.0) + class FormatFunctionsTestCase(unittest.TestCase): def setUp(self):