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Re: [PATCH] Set up errno properly for yn

On Mon, 28 May 2012, Marek Polacek wrote:

> This is what I have right now.  But it still isn't applicable, I'm
> afraid, because I had to guard the errno test with #ifndef TEST_LDOUBLE.
> If I don't do this, I get failures:

In such a case:

* You've found a separate bug in the course of fixing a bug.  So file it 
in Bugzilla so people can find it there as a known bug.

* When adding a test that's disabled for TEST_LDOUBLE because of that 
separate bug, include a comment by the disabling that references "bug 
NNNNN" for whatever the number is, so it's easy to find and removing the 
disabling when the separate bug is fixed.

> testing long double (without inline functions)
> Failure: yn (10, min_value) == -inf: Exception "Invalid operation" set
> Failure: Test: yn (10, min_value) == -inf
> Result:
>  is:         -nan  -nan
>  should be:  -inf  -inf

My guess is that the overflow of yn has involved an internal computation 
such as Inf - Inf or Inf / Inf that generated NaNs.  It looks rather like 
the ynl code that tries to stop this happening is confused about 
GET_LDOUBLE_WORDS, which appears to set the sign+exponent value to a 
*sign-extended* value (so 0xffffffff not 0xffff for -Inf).

Joseph S. Myers

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