[Python-checkins] r71837 - python/trunk/Lib/test/test_math.py
mark.dickinson
python-checkins at python.org
Fri Apr 24 18:34:15 CEST 2009
Author: mark.dickinson
Date: Fri Apr 24 18:34:14 2009
New Revision: 71837
Log:
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.
Modified:
python/trunk/Lib/test/test_math.py
Modified: python/trunk/Lib/test/test_math.py
==============================================================================
--- python/trunk/Lib/test/test_math.py (original)
+++ python/trunk/Lib/test/test_math.py Fri Apr 24 18:34:14 2009
@@ -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]
@@ -364,6 +369,10 @@
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.skipUnless(not 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
@@ -373,14 +382,6 @@
# 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.
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