[Python-checkins] r87032 - in python/branches/py3k: Lib/test/test_float.py Misc/NEWS Objects/floatobject.c
mark.dickinson
python-checkins at python.org
Sat Dec 4 13:25:30 CET 2010
Author: mark.dickinson
Date: Sat Dec 4 13:25:30 2010
New Revision: 87032
Log:
Issue #10596: Fix float.__mod__ to have the same behaviour as
float.__divmod__ with respect to signed zeros.
Modified:
python/branches/py3k/Lib/test/test_float.py
python/branches/py3k/Misc/NEWS
python/branches/py3k/Objects/floatobject.c
Modified: python/branches/py3k/Lib/test/test_float.py
==============================================================================
--- python/branches/py3k/Lib/test/test_float.py (original)
+++ python/branches/py3k/Lib/test/test_float.py Sat Dec 4 13:25:30 2010
@@ -197,6 +197,26 @@
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
Modified: python/branches/py3k/Misc/NEWS
==============================================================================
--- python/branches/py3k/Misc/NEWS (original)
+++ python/branches/py3k/Misc/NEWS Sat Dec 4 13:25:30 2010
@@ -10,6 +10,10 @@
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.
Modified: python/branches/py3k/Objects/floatobject.c
==============================================================================
--- python/branches/py3k/Objects/floatobject.c (original)
+++ python/branches/py3k/Objects/floatobject.c Sat Dec 4 13:25:30 2010
@@ -600,10 +600,20 @@
}
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);
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