Fix clog / clog10 sign of zero result in round-downward mode (bug 16789)

[Andreas Jaeger]

On 04/01/2014 05:46 PM, Joseph S. Myers wrote:
> This patch fixes bug 16789, incorrect sign of (real part) zero result
> from clog and clog10 in round-downward mode, arising from that real
> part being computed as 0 - 0.  To ensure that an underflow exception
> occurred, the code used an underflowing value (the next term in the
> series for log1p) in arithmetic computing the real part of the result,
> yielding the problematic 0 - 0 computation in some cases even when the
> mathematical result would be small but positive.  The patch changes
> this code to use the math_force_eval approach to ensuring that an
> underflowing computation actually occurs.  Tests of clog and clog10
> are enabled in all rounding modes.

Thanks,
Andreas
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