From de782a1d11c7373a62007b618049b8c1c5dc2d75 Mon Sep 17 00:00:00 2001 From: "mark.dickinson" Date: Fri, 24 Apr 2009 16:34:14 +0000 Subject: [PATCH] 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. git-svn-id: http://svn.python.org/projects/python/trunk@71837 6015fed2-1504-0410-9fe1-9d1591cc4771 --- Lib/test/test_math.py | 17 +++++++++-------- 1 file changed, 9 insertions(+), 8 deletions(-) diff --git a/Lib/test/test_math.py b/Lib/test/test_math.py index c82c775cce..64345fc0dd 100644 --- a/Lib/test/test_math.py +++ b/Lib/test/test_math.py @@ -13,6 +13,11 @@ NAN = float('nan') 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 @@ class MathTests(unittest.TestCase): 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 @@ class MathTests(unittest.TestCase): # 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. -- 2.11.4.GIT