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Re: Test failure on Mac OS 10.8.2

From: Eric Blake
Subject: Re: Test failure on Mac OS 10.8.2
Date: Fri, 08 Mar 2013 12:50:08 -0700
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:17.0) Gecko/20130219 Thunderbird/17.0.3

On 03/08/2013 10:47 AM, Paul Eggert wrote:

> OK, thanks, it looks like the gnulib test is being too picky:
> it's insisting on round-to-even but POSIX says the rounding
> is implementation-defined.  Mac OS should probably be rounding
> to even but that's not our job.  I pushed the following patch.

Where do you read that?  I see that POSIX says that rounding is
implementation-defined for f, F, e, E.  Then for a and A, it says:

For a and A conversions, if FLT_RADIX is not a power of 2 and the result
is not exactly representable in the given precision, the result should
be one of the two adjacent numbers in hexadecimal floating style with
the given precision, with the extra stipulation that the error should
have a correct sign for the current rounding direction.

But appears to say nothing about the case when FLT_RADIX _is_ a power of
2, yet the result is not exactly representable.  Still, by
extrapolation, I would assume that we want the error to be in the
correct direction for the current rounding, and since both round-to-even
and round-to-plus-inf would result in 1.5 becoming 2, not 1, I think
this is a bug in Mac OS.

But until we fix gnulib to work around Mac's rounding bug, I'm okay with
relaxing the test.

Eric Blake   eblake redhat com    +1-919-301-3266
Libvirt virtualization library http://libvirt.org

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