Author mark.dickinson
Recipients mark.dickinson
Date 2008-05-21.20:36:53
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Message-id <1211402217.78.0.330998218554.issue2937@psf.upfronthosting.co.za>
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On some older Intel 32-bit hardware, under Linux, floating-point 
operations don't always give correctly rounded results.  Here's an 
example involving addition, on SuSE Linux 10.2/Xeon.

Python 2.6a3+ (trunk:63521, May 21 2008, 15:40:39) 
[GCC 4.1.2 20061115 (prerelease) (SUSE Linux)] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>> 1e16 + 2.999
10000000000000002.0
>>> 1e16 + 2.9999
10000000000000004.0

The second result should really be 1e16+2., not 1e16+4.  This appears to 
be related to this GCC issue:

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=323

Various fixes are possible.  One possible fix is to add the -ffloat-
store flag to the gcc options.  Another is to use the information in 
fpu_control.h, if available, to set the precision control.  Yet another 
is to sprinkle some 'volatile' modifiers throughout floatobject.c.

It's not clear to me that this *should* be fixed, but I think the 
problem should at least be documented.  Hence this bug report.
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Date User Action Args
2008-05-21 20:36:59mark.dickinsonsetspambayes_score: 0.00179302 -> 0.00179302
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2008-05-21 20:36:57mark.dickinsonsetspambayes_score: 0.00179302 -> 0.00179302
messageid: <1211402217.78.0.330998218554.issue2937@psf.upfronthosting.co.za>
2008-05-21 20:36:56mark.dickinsonlinkissue2937 messages
2008-05-21 20:36:53mark.dickinsoncreate