Noam Raphael added the comment: 2007/12/13, Guido van Rossum <[EMAIL PROTECTED]>: > > > Ok, so if I understand correctly, the ideal thing would be to > > implement decimal to binary conversion by ourselves. This would make > > str <-> float conversion do the same thing on all platforms, and would > > make repr(1.1)=='1.1'. This would also allow us to define exactly how > > floats operate, with regard to infinities and NaNs. All this is for > > IEEE-754 platforms -- for the rare platforms which don't support it, > > the current state remains. > > Does doubledigits.c not work for non-754 platforms?
No. It may be a kind of an oops, but currently it just won't compile on platforms which it doesn't recognize, and it only recognizes 754 platforms. > > > 2. Keep the binary to shortest decimal routine and use it only when we > > know that the system's decimal to binary routine is correctly rounding > > (we can check - perhaps Microsoft has changed theirs?) > > Tim says you can't check (test) for this -- you have to prove it from > source, or trust the vendor's documentation. I would have no idea > where to find this documented. > The program for testing floating point compatibility is in http://www.cant.ua.ac.be/ieeecc754.html To run it, on my computer, I used: ./configure -target Conversions -platform IntelPentium_cpp make ./IeeeCC754 -d -r n -n x Conversion/testsets/d2bconvd less ieee.log This tests only doubles, round to nearest, and ignores flags which should be raised to signal inexact conversion. You can use any file in Conversions/testsets/d2b* - I chose this one pretty randomly. It turns out that even on my gcc 4.1.3 it finds a few floats not correctly rounded. :( Anyway, it can be used to test other platforms. If not by the executable itself, we can pretty easily write a python program which uses the test data. I don't know what exactly the errors with gcc 4.1.3 mean - is there a problem with the algorithm of glibc, or perhaps the testing program didn't set some flag? __________________________________ Tracker <[EMAIL PROTECTED]> <http://bugs.python.org/issue1580> __________________________________ _______________________________________________ Python-bugs-list mailing list Unsubscribe: http://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
