diff options
| -rw-r--r-- | Lib/test/test_float.py | 20 | ||||
| -rw-r--r-- | Misc/NEWS | 4 | ||||
| -rw-r--r-- | Objects/floatobject.c | 18 |
3 files changed, 38 insertions, 4 deletions
diff --git a/Lib/test/test_float.py b/Lib/test/test_float.py index 9bcd63d..ddf93bc 100644 --- a/Lib/test/test_float.py +++ b/Lib/test/test_float.py @@ -197,6 +197,26 @@ class GeneralFloatCases(unittest.TestCase): self.assertEqual((a, copysign(1.0, a)), (b, copysign(1.0, b))) @requires_IEEE_754 + def test_float_mod(self): + # Check behaviour of % operator for IEEE 754 special cases. + # In particular, check signs of zeros. + mod = operator.mod + + self.assertEqualAndEqualSign(mod(-1.0, 1.0), 0.0) + self.assertEqualAndEqualSign(mod(-1e-100, 1.0), 1.0) + self.assertEqualAndEqualSign(mod(-0.0, 1.0), 0.0) + self.assertEqualAndEqualSign(mod(0.0, 1.0), 0.0) + self.assertEqualAndEqualSign(mod(1e-100, 1.0), 1e-100) + self.assertEqualAndEqualSign(mod(1.0, 1.0), 0.0) + + self.assertEqualAndEqualSign(mod(-1.0, -1.0), -0.0) + self.assertEqualAndEqualSign(mod(-1e-100, -1.0), -1e-100) + self.assertEqualAndEqualSign(mod(-0.0, -1.0), -0.0) + self.assertEqualAndEqualSign(mod(0.0, -1.0), -0.0) + self.assertEqualAndEqualSign(mod(1e-100, -1.0), -1.0) + self.assertEqualAndEqualSign(mod(1.0, -1.0), -0.0) + + @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 @@ -10,6 +10,10 @@ What's New in Python 3.2 Beta 1? Core and Builtins ----------------- +- Issue #10596: Fix float.__mod__ to have the same behaviour as + float.__divmod__ with respect to signed zeros. -4.0 % 4.0 should be + 0.0, not -0.0. + - Issue #1772833: Add the -q command-line option to suppress copyright and version output in interactive mode. diff --git a/Objects/floatobject.c b/Objects/floatobject.c index d5a3c7e..7cbb240 100644 --- a/Objects/floatobject.c +++ b/Objects/floatobject.c @@ -600,10 +600,20 @@ float_rem(PyObject *v, PyObject *w) } PyFPE_START_PROTECT("modulo", return 0) mod = fmod(vx, wx); - /* note: checking mod*wx < 0 is incorrect -- underflows to - 0 if wx < sqrt(smallest nonzero double) */ - if (mod && ((wx < 0) != (mod < 0))) { - mod += wx; + if (mod) { + /* ensure the remainder has the same sign as the denominator */ + if ((wx < 0) != (mod < 0)) { + mod += wx; + } + } + else { + /* the remainder is zero, and in the presence of signed zeroes + fmod returns different results across platforms; ensure + it has the same sign as the denominator; we'd like to do + "mod = wx * 0.0", but that may get optimized away */ + mod *= mod; /* hide "mod = +0" from optimizer */ + if (wx < 0.0) + mod = -mod; } PyFPE_END_PROTECT(mod) return PyFloat_FromDouble(mod); |