Fix casinh, casin inaccuracy from cancellation (bug 14994)

[Andreas Jaeger]

On 01/04/2013 02:39 AM, Joseph S. Myers wrote:
> Bug 14994 is inaccuracy of casinh (and so of casin, which is
> implemented to call casinh) for large arguments with negative real
> part, because of cancellation in the formula clog (z + csqrt (1 +
> z*z)) when the square root is close to -z instead of close to z.
>
> This patch fixes this bug by reducing arguments to the first quadrant,
> so that the square root is also in the first quadrant and no
> cancellation occurs.  Reducing arguments to the first quadrant will
> also help simplify fixes for other casinh bugs (overflows, underflows
> and inaccuracy near the line segment from -i to i - the last of these
> is bug 10357).
>
> Tested x86_64 and x86 and ulps updated accordingly.

Thanks, this is fine,

Andreas
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