Fix expm1 spurious underflow exceptions (bug 6778)

[Andreas Jaeger]

On 07/06/2012 12:08 AM, Joseph S. Myers wrote:
> Bug 6778 is spurious underflow from expm1 (x86 versions, including
> x86_64 for expm1l only) for large negative arguments (where exp would
> underflow, but expm1 should return a value very close to -1).
>
> This patch fixes this by adding appropriate checks for large negative
> arguments to each function.  (The new tests of expm1 for negative
> arguments are intended to cover ranges around where the result starts
> to round to -1 exactly for float, double and the supported long double
> formats.)
>
> Tested x86 and x86_64 and ulps updated accordingly.
>
> 2012-07-05  Joseph Myers  <joseph@codesourcery.com>
>
> 	[BZ #6778]
> 	* sysdeps/i386/fpu/s_expm1.S (__expm1): Check for large negative
> 	inputs and return -1 for them.  Do not check for +Inf in case not
> 	reachable for +Inf.
> 	* sysdeps/i386/fpu/s_expm1f.S (__expm1f): Likewise.
> 	* sysdeps/i386/fpu/e_expl.S [USE_AS_EXPM1L] (csat): Do not define.
> 	(IEEE754_EXPL) [USE_AS_EXPM1L]: Check for large negative inputs
> 	and return -1 for them.  Do not check for +Inf in case not
> 	reachable for +Inf.
> 	* sysdeps/x86_64/fpu/e_expl.S [USE_AS_EXPM1L] (csat): Do not
> 	define.
> 	(IEEE754_EXPL) [USE_AS_EXPM1L]: Check for large negative inputs
> 	and return -1 for them.  Do not check for +Inf in case not
> 	reachable for +Inf.
> 	* math/libm-test.inc (expm1_test): Add more tests.  Do not allow
> 	spurious underflow.
> 	* sysdeps/i386/fpu/libm-test-ulps: Update.
> 	* sysdeps/x86_64/fpu/libm-test-ulps: Likewise.

Thanks, this is ok,

Andreas
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