Merged revisions 87032 via svnmerge from

svn+ssh://pythondev@svn.python.org/python/branches/py3k

........
  r87032 | mark.dickinson | 2010-12-04 12:25:30 +0000 (Sat, 04 Dec 2010) | 3 lines

  Issue #10596: Fix float.__mod__ to have the same behaviour as
  float.__divmod__ with respect to signed zeros.
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This commit is contained in:
Mark Dickinson 2010-12-04 12:30:41 +00:00
parent c1d0ed2907
commit ecf8ec67ce
3 changed files with 38 additions and 4 deletions

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@ -161,6 +161,26 @@ class GeneralFloatCases(unittest.TestCase):
# distingishes -0.0 and 0.0.
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.

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@ -9,6 +9,10 @@ What's New in Python 2.7.2?
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.
Library
-------

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@ -716,10 +716,20 @@ float_rem(PyObject *v, PyObject *w)
#endif
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);