[issue5593] test_math.testFsum failure on release30-maint

[Antoine Pitrou]

Antoine Pitrou <pitrou at free.fr> added the comment:

> My best guess is that you somehow ended up in a situation where the math 
> module was using the x87 FPU for floating-point, while the interpreter 
> core was using SSE2.  Is this possible?
> 

That would be the reverse, since this occurred on a 32-bit build, i.e.
the interpreter core was using x87. But I don't understand how a 64-bit
module could be loaded by a 32-bit executable (I did check that
sys.maxsize was 2**31 - 1).

> fsum is a bit broken on systems with double rounding problems.  So
there's 
> a pair of lines in testFsum that look like:
> 
> if 1e16+2.0 != 1e16+2.9999:
>     return


Wouldn't it be a problem with stale pyc files then? The result of each
addition is stored as a constant when the code is compiled. Note how the
constants arrays differ:

64-bit:

>>> def f():
...   return 1e16+2.9999
... 
>>> dis.dis(f)
  2           0 LOAD_CONST               3 (10000000000000002.0) 
              3 RETURN_VALUE         
>>> zlib.crc32(marshal.dumps(f.__code__.co_consts))
2292868100

32-bit:

>>> def f():    
...   return 1e16+2.9999
... 
>>> dis.dis(f)  
  2           0 LOAD_CONST               3 (10000000000000004.0) 
              3 RETURN_VALUE         
>>> zlib.crc32(marshal.dumps(f.__code__.co_consts))
103113703

----------
resolution: invalid -> 
status: closed -> open

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Python tracker <report at bugs.python.org>
<http://bugs.python.org/issue5593>
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