Re: One-liner breaks "strtold" in XCode 2.4
Re: One-liner breaks "strtold" in XCode 2.4
- Subject: Re: One-liner breaks "strtold" in XCode 2.4
- From: Eric Albert <email@hidden>
- Date: Tue, 28 Nov 2006 19:52:18 -0800
On Nov 28, 2006, at 6:18 PM, Jay Reynolds Freeman wrote:
My code establishes that a numeric string which manifestly is
not a nan is interpreted as a nan by "strtold". I am running
on a Macbook 1,1 with OS 10.4.8. The version of gcc is that
which came with the download of XCode 2.4.1, which is gcc-4.0;
however, I believe the problem is in a library which is not
part of gcc per se. I think the library is provided by Apple.
I have done a google search for information about this bug,
and turned up some possible reports that the bug may be related
to the fact that "long doubles" are in IEEE 80-bit format on
the Macbook. Reports indicate that in architectures using
IEEE 64-bit format for long double, the problem does not
occur. Thus if you try to duplicate my bug, your mileage
may vary depending on what processor you are using.
In particular, if your compiler reports that
sizeof( long double ) is 8 bytes, you may not see the bug.
(IEEE 80-bits take at least 10 bytes, and maybe more if
data must be word-aligned.)
On Intel processors, Mac OS X uses an 80-bit long double, stuffed in
a 16-byte data type in which 6 bytes are ignored. Whether it's an
IEEE-754 format or not isn't something I know enough to comment on,
but it's Intel's native 80-bit floating point type.
If you think there's a bug in the strtold implementation on Mac OS X,
the best thing to do is to file a bug report with a reproducible test
case at <http://bugreport.apple.com/>.
-Eric
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