[Python-checkins] r63553 - python/trunk/Lib/test/test_math.py

[mark.dickinson]

Author: mark.dickinson
Date: Fri May 23 14:07:36 2008
New Revision: 63553

Log:
Skip math.sum tests on non IEEE 754 platforms, and on IEEE 754 platforms 
that exhibit the problem described in issue #2937. 


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 May 23 14:07:36 2008
@@ -631,6 +631,22 @@
         self.assert_(math.isnan(math.sqrt(NAN)))
 
     def testSum(self):
+        # math.sum relies on exact rounding for correct operation.
+        # There's a known problem with IA32 floating-point that causes
+        # inexact rounding in some situations, and will cause the
+        # math.sum tests below to fail; see issue #2937.  On non IEEE
+        # 754 platforms, and on IEEE 754 platforms that exhibit the
+        # 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+2.999 != 1e16+2.9999:
+            return
+
         # Python version of math.sum algorithm, for comparison
         def msum(iterable):
             """Full precision sum of values in iterable.  Returns the value of