Issue 1678380: fix a bug identifying -0.0 and 0.0
diff --git a/Lib/test/test_float.py b/Lib/test/test_float.py
index fb47db8..2f0d784 100644
--- a/Lib/test/test_float.py
+++ b/Lib/test/test_float.py
@@ -99,6 +99,27 @@
('<f', LE_FLOAT_NAN)]:
struct.unpack(fmt, data)
+ if float.__getformat__("double").startswith("IEEE"):
+ def test_negative_zero(self):
+ import math
+ def pos_pos():
+ return 0.0, math.atan2(0.0, -1)
+ def pos_neg():
+ return 0.0, math.atan2(-0.0, -1)
+ def neg_pos():
+ return -0.0, math.atan2(0.0, -1)
+ def neg_neg():
+ return -0.0, math.atan2(-0.0, -1)
+ self.assertEquals(pos_pos(), neg_pos())
+ self.assertEquals(pos_neg(), neg_neg())
+
+ if float.__getformat__("double").startswith("IEEE"):
+ def test_underflow_sign(self):
+ import math
+ # check that -1e-1000 gives -0.0, not 0.0
+ self.assertEquals(math.atan2(-1e-1000, -1), math.atan2(-0.0, -1))
+ self.assertEquals(math.atan2(float('-1e-1000'), -1),
+ math.atan2(-0.0, -1))
def test_main():
test_support.run_unittest(
diff --git a/Misc/NEWS b/Misc/NEWS
index 00db9af..dd06f60 100644
--- a/Misc/NEWS
+++ b/Misc/NEWS
@@ -12,6 +12,9 @@
Core and builtins
-----------------
+- Issue #1678380: distinction between 0.0 and -0.0 was lost during constant
+ folding optimization. This was a regression from Python 2.4.
+
- Issue #1882: when compiling code from a string, encoding cookies in the
second line of code were not always recognized correctly.
diff --git a/Python/compile.c b/Python/compile.c
index ce19aa9..0e824ca 100644
--- a/Python/compile.c
+++ b/Python/compile.c
@@ -1567,7 +1567,20 @@
Py_ssize_t arg;
/* necessary to make sure types aren't coerced (e.g., int and long) */
- t = PyTuple_Pack(2, o, o->ob_type);
+ /* _and_ to distinguish 0.0 from -0.0 e.g. on IEEE platforms */
+ if (PyFloat_Check(o)) {
+ double d = PyFloat_AS_DOUBLE(o);
+ unsigned char* p = (unsigned char*) &d;
+ /* all we need is to make the tuple different in either the 0.0
+ * or -0.0 case from all others, just to avoid the "coercion".
+ */
+ if (*p==0 && p[sizeof(double)-1]==0)
+ t = PyTuple_Pack(3, o, o->ob_type, Py_None);
+ else
+ t = PyTuple_Pack(2, o, o->ob_type);
+ } else {
+ t = PyTuple_Pack(2, o, o->ob_type);
+ }
if (t == NULL)
return -1;