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Re: floor, ceil, trunc, round, minus zero, and alpha

From: Eric Blake
Subject: Re: floor, ceil, trunc, round, minus zero, and alpha
Date: Mon, 20 Dec 2010 07:47:20 -0700
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On 12/20/2010 06:55 AM, Bruno Haible wrote:
> Hi,
> On 2010-11-04, Eric added tests checking the sign of the minus zero value
> of floor, ceil, trunc, round.
> <http://lists.gnu.org/archive/html/bug-gnulib/2010-11/msg00020.html>
> <http://lists.gnu.org/archive/html/bug-gnulib/2010-11/msg00029.html>
> These tests
>   - fail on OSF/1 with DEC Alpha CPU,
>   - are marked as [MX] in POSIX [1][2][3][4], that is, an optional feature
>     not contained in ISO C 99,

[MX] means that the behavior is required on platforms that claim IEC
60559 conformance (aka IEEE 754 format); it means that you fully
implement the otherwise-optional Appendix F of the C99 standard.

>   - make little sense for 'ceil' from a mathematical point of view:
>     ceil is a monotonically increasing function but POSIX wants
>     ceil(-0.5) = 0.0 and ceil(-0.0) = -0.0,

I'll raise that point with the Austin group.

Eric Blake   address@hidden    +1-801-349-2682
Libvirt virtualization library http://libvirt.org

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