Mark Dickinson <[EMAIL PROTECTED]> added the comment: Okay; so this is definitely not a Python bug---it's a well-known and well-documented problem with IA32 floating-point. And I accept that it's really not Python's responsibility to document this, either.
Nevertheless, it was a surprise to me when my (supposedly IEEE 754 compliant) Pentium 4 box produced this. I probably shouldn't have been surprised. I'm aware of issues with 80-bit extended precision when programming in C, but naively expected that Python would be largely immune from these, since it's always going to force intermediate results from (80-bit) floating-point registers into (64-bit) memory slots. There's an excellent recent article by David Monniaux, "The pitfalls of verifying floating-point computations.", that's available online at http://hal.archives-ouvertes.fr/hal-00128124 that explains exactly what's going on here (it's a case of double- rounding, as described in section 3.1.2 of that paper). Do you think a documentation patch that added this reference, along with the oft-quoted "What Every Computer Scientist Should Know About Floating-Point Arithmetic" by David Goldberg, to Appendix B of the tutorial would be acceptable? One other thing that's worth mentioning: on Pentium 4 and later, the gcc flags "-mfpmath=sse -msse2" appear to fix the problem, by forcing gcc to use the SSE floating-point unit instead of the x87-derived one. In any case, I guess this report should be closed as 'invalid', but I hope that at least others who encounter this problem manage to find this bug report. __________________________________ Tracker <[EMAIL PROTECTED]> <http://bugs.python.org/issue2937> __________________________________ _______________________________________________ Python-bugs-list mailing list Unsubscribe: http://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
