Fix catan, catanh, __ieee754_logf in round-downward mode (bug 16799, bug 16800)

[Andreas Jaeger]

On 04/02/2014 04:26 PM, Joseph S. Myers wrote:
> This patch fixes incorrect results from catan and catanh of certain
> special inputs in round-downward mode (bug 16799), and incorrect
> results of __ieee754_logf (+/-0) in round-downward mode (bug 16800)
> that show up through catan/catanh when tested in all rounding modes,
> but not directly in the testing for logf because the bug gets hidden
> by the wrappers.
> 
> Both bugs involve a zero that should be +0 being -0 instead: one
> computed as (1-x)*(1+x) in the catan/catanh case, and one as (x-x) in
> the logf case.  The fixes ensure positive zero is used.  Testing of
> catan and catanh in all rounding modes is duly enabled.
> 
> I expect there are various other bugs in special cases in __ieee754_*
> functions that are normally hidden by the wrappers but would show up
> for testing with -lieee (or in future with -fno-math-errno if we
> replace -lieee and _LIB_VERSION with compile-time redirection to new
> *_noerrno symbol names).

Thanks,
Andreas
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