[ python-Bugs-1481296 ] long(float('nan'))!=0L

[SourceForge.net]

Bugs item #1481296, was opened at 2006-05-03 19:39
Message generated for change (Comment added) made by mwh
You can respond by visiting: 
https://sourceforge.net/tracker/?func=detail&atid=105470&aid=1481296&group_id=5470

Please note that this message will contain a full copy of the comment thread,
including the initial issue submission, for this request,
not just the latest update.
Category: Python Interpreter Core
Group: Python 2.3
Status: Open
Resolution: None
Priority: 5
Submitted By: Erik Dahl (edahl)
Assigned to: Nobody/Anonymous (nobody)
Summary: long(float('nan'))!=0L

Initial Comment:
on all platforms I can test long(float('nan'))=0L

But on maxos X intel long(float('nan'))!=0L

it returns:

000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000L

This is a problem because:

>>> 344 - long(float('nan'))    
Objects/longobject.c:1645: failed assertion `borrow == 0'
Abort trap




----------------------------------------------------------------------

>Comment By: Michael Hudson (mwh)
Date: 2006-05-09 19:47

Message:
Logged In: YES 
user_id=6656

Nevertheless, assuming that a compiler implements the relavent standards (i.e. 
Appendix F of C99) it's pretty clear that what PyLong_FromDouble does with a 
nan is pretty random.  frexp(dval, &expo); for dval nan stores an unspecified 
value in expo which is then used to compute the length of the resulting long.  If 
the unspecified value is large-ish and positive, hilarity ensues.

----------------------------------------------------------------------

Comment By: Tim Peters (tim_one)
Date: 2006-05-03 20:09

Message:
Logged In: YES 
user_id=31435

Try it on Windows and you'll get:

>>> long(float('nan'))
Traceback (most recent call last):
  File "<stdin>", line 1, in ?
ValueError: invalid literal for float(): nan

Nothing about the behavior of NaNs, infinities, or signed
zeroes is defined or guaranteed by Python.  You use them at
your own risk, and their behavior does vary wildly in
practice (according to the HW, OS, C compiler, C library,
and even the C compiler flags specified when compiling Python).

----------------------------------------------------------------------

You can respond by visiting: 
https://sourceforge.net/tracker/?func=detail&atid=105470&aid=1481296&group_id=5470