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Author noam
Recipients christian.heimes, gvanrossum, nascheme, noam, rhettinger, tim.peters
Date 2007-12-13.09:12:25
SpamBayes Score 0.00076558255
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Message-id <>
In-reply-to <>
2007/12/13, Guido van Rossum <>:
> > 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
> > 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

To run it, on my computer, I used:
./configure -target Conversions -platform IntelPentium_cpp
./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?
Date User Action Args
2007-12-13 09:12:28noamsetspambayes_score: 0.000765583 -> 0.00076558255
recipients: + noam, gvanrossum, tim.peters, nascheme, rhettinger, christian.heimes
2007-12-13 09:12:27noamlinkissue1580 messages
2007-12-13 09:12:25noamcreate