Merged revisions 71837-71838 via svnmerge from
svn+ssh://pythondev@svn.python.org/python/trunk
........
r71837 | mark.dickinson | 2009-04-24 17:34:14 +0100 (Fri, 24 Apr 2009) | 4 lines
Issue #5593: Use more robust test for double-rounding in test_fsum.
While we're at it, use new unittest.skipUnless decorator to
implement skipping for that test.
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r71838 | mark.dickinson | 2009-04-24 17:37:22 +0100 (Fri, 24 Apr 2009) | 2 lines
Remove unnecessary double negative
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diff --git a/Lib/test/test_math.py b/Lib/test/test_math.py
index 9e646ac..d74f01f 100644
--- a/Lib/test/test_math.py
+++ b/Lib/test/test_math.py
@@ -13,6 +13,11 @@
INF = float('inf')
NINF = float('-inf')
+# detect evidence of double-rounding: fsum is not always correctly
+# rounded on machines that suffer from double rounding.
+x, y = 1e16, 2.9999 # use temporary values to defeat peephole optimizer
+HAVE_DOUBLE_ROUNDING = (x + y == 1e16 + 4)
+
# locate file with test values
if __name__ == '__main__':
file = sys.argv[0]
@@ -359,6 +364,10 @@
self.assertEquals(math.frexp(NINF)[0], NINF)
self.assert_(math.isnan(math.frexp(NAN)[0]))
+ @unittest.skipUnless(float.__getformat__("double").startswith("IEEE"),
+ "test requires IEEE 754 doubles")
+ @unittest.skipIf(HAVE_DOUBLE_ROUNDING,
+ "fsum is not exact on machines with double rounding")
def testFsum(self):
# math.fsum relies on exact rounding for correct operation.
# There's a known problem with IA32 floating-point that causes
@@ -368,14 +377,6 @@
# problem described in issue #2937, we simply skip the whole
# test.
- if not float.__getformat__("double").startswith("IEEE"):
- return
-
- # on IEEE 754 compliant machines, both of the expressions
- # below should round to 10000000000000002.0.
- if 1e16+2.0 != 1e16+2.9999:
- return
-
# Python version of math.fsum, for comparison. Uses a
# different algorithm based on frexp, ldexp and integer
# arithmetic.