Message 67174 - Python tracker

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In-reply-to
Author	mark.dickinson
Recipients	mark.dickinson
Date	2008年05月21日.20:36:53
SpamBayes Score	0.0017930194
Marked as misclassified	No
Message-id	<1211402217.78.0.330998218554.issue2937@psf.upfronthosting.co.za>

Content
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.

Content

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.

History
Date	User	Action	Args
2008年05月21日 20:36:59	mark.dickinson	set	spambayes_score: 0.00179302 -> 0.0017930194 recipients: + mark.dickinson
2008年05月21日 20:36:57	mark.dickinson	set	spambayes_score: 0.00179302 -> 0.00179302 messageid: <1211402217.78.0.330998218554.issue2937@psf.upfronthosting.co.za>
2008年05月21日 20:36:56	mark.dickinson	link	issue2937 messages
2008年05月21日 20:36:53	mark.dickinson	create

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