Issue 1492293: Wierd Floating Point on FreeBSD4 (original) (raw)
Created on 2006-05-21 00:34 by david_abrahams, last changed 2022-04-11 14:56 by admin. This issue is now closed.
Messages (9)
Author: David Abrahams (david_abrahams)
Date: 2006-05-21 00:34
This is just about the weirdest thing I've ever seen. Python 2.4.2 (#1, Jan 17 2006, 09:30:19) [GCC 2.95.2 19991024 (release)] on freebsd4
---- nan.py ----
inf = 1e300000
nan = inf/inf
print nan
---- nan.py ----
---- tst.py ----
import nan
---- tst.py ----
% python -c "import nan"
NaN
% python -c "import tst"
NaNNow I edit tst.py
---- tst.py ----
#
import nan
---- tst.py ----
% python -c "import nan"
Traceback (most recent call last):
File "<string>", line 1, in ?
File "nan.py", line 2, in ?
nan = inf/inf
ZeroDivisionError: float division
% python -c "import tst"
Traceback (most recent call last):
File "<string>", line 1, in ?
File "tst.py", line 1, in ?
import nan
File "nan.py", line 2, in ?
nan = inf/inf
ZeroDivisionError: float division
% rm *.pyc
% python -c "import tst"
NaN
% python -c "import nan"
Traceback (most recent call last):
File "<string>", line 1, in ?
File "nan.py", line 2, in ?
nan = inf/inf
ZeroDivisionError: float division
% python -c "import tst"
Traceback (most recent call last):
File "<string>", line 1, in ?
File "tst.py", line 1, in ?
import nan
File "nan.py", line 2, in ?
nan = inf/inf
ZeroDivisionError: float divisionAuthor: Tim Peters (tim.peters) * 
Date: 2006-05-21 15:09
Logged In: YES user_id=31435
Python doesn't know anything about IEEE special values, and in particular what the marshal format (used for code objects) does with infinities and NaNs is a platform-dependent accident.
Try changing
inf = 1e300000
to
inf = 1e300 * 1e300
to stop Python from trying to marshal/unmarshal a floating infinity on that box. I bet your problems will go away then.
Author: Martin v. Löwis (loewis) *
Date: 2006-05-22 09:32
Logged In: YES user_id=21627
Closing this as "not a bug". Notice that this judgement is difficult to make, as the report is incomplete: you report what you did (good), what happened (good), but not what you expected to happen, or why you think the behaviour is incorrect - only that it is "weird". As Tim mentioned indirectly, this is intentional.
Author: Michael Hudson (mwh)
Date: 2006-05-22 10:00
Logged In: YES user_id=6656
Also, this probably won't be a problem in 2.5.
Author: Tim Peters (tim.peters) *
Date: 2006-05-22 10:28
Logged In: YES user_id=31435
mwh: Heh. It's sure not better under Windows on current trunk:
C:\Code\python\PCbuild>python -c "import nan" -1.#IND Exception exceptions.SystemError: 'frexp() result out of range' in 'garbage collection' ignored Fatal Python error: unexpected exception during garbage collection
And now that the .pyc file exists:
C:\Code\python\PCbuild>python -c "import nan" Traceback (most recent call last): File "", line 1, in ValueError: bad marshal data
This is nan.py, BTW:
""" inf = 1e300000 nan = inf/inf print nan """
Changing that to "inf = 1e300*1e300" doesn't help in the trunk, because of its more ambitious constant folding.
Author: Michael Hudson (mwh)
Date: 2006-05-22 10:45
Logged In: YES user_id=6656
Huh what? That code is supposed to be dead on real systems now. What does this say for you:
float.getformat('double') 'IEEE, big-endian'
? I take it test_float still passes.
Author: Tim Peters (tim.peters) *
Date: 2006-05-22 10:52
Logged In: YES user_id=31435
Hmm:
C:\Code\python\PCbuild>python Python 2.5a2 (trunk:46052, May 19 2006, 20:53:33) [MSC v.1310 32 bit (Intel)] on win32
float.getformat('double') 'unknown'
Author: Tim Peters (tim.peters) *
Date: 2006-05-22 10:55
Logged In: YES user_id=31435
BTW, I suspect SIZEOF_DOUBLE simply isn't defined on Windows. I'll check that later.
Author: Michael Hudson (mwh)
Date: 2006-05-22 10:58
Logged In: YES user_id=6656
Oh right.
The "Fatal Python error: unexpected exception during garbage collection" thing is still a bit disturbing though...