Fix ctanh (0 + i NaN), ctanh (0 + i Inf) (bug 22568, DR#471).

As per C11 DR#471, ctanh (0 + i NaN) and ctanh (0 + i Inf) should
return 0 + i NaN (with "invalid" exception in the second case but not
the first), not NaN + i NaN.  This has corresponding implications for
ctan since its special cases are defined by ctan (z) = -i ctanh (iz).
This patch implements these cases for ctanh and ctan, updating
tests accordingly.

Tested for x86_64.

	[BZ #22568]
	* math/s_ctan_template.c (M_DECL_FUNC (__ctan)): Set imaginary
	part of result to imaginary part of argument if it is zero and the
	real part of the argument is not finite.
	* math/s_ctanh_template.c (M_DECL_FUNC (__ctanh)): Set real part
	of result to real part of argument if it is zero and the imaginary
	part of the argument is not finite.

1 files changed, 4 insertions, 1 deletions

diff --git a/math/s_ctan_template.c b/math/s_ctan_template.c
index 723156eed4..644d7e696d 100644
--- a/math/s_ctan_template.c
+++ b/math/s_ctan_template.c
@@ -49,7 +49,10 @@ M_DECL_FUNC (__ctan) (CFLOAT x)
       else
 	{
 	  __real__ res = M_NAN;
-	  __imag__ res = M_NAN;
+	  if (__imag__ x == 0)
+	    __imag__ res = __imag__ x;
+	  else
+	    __imag__ res = M_NAN;
 
 	  if (isinf (__real__ x))
 	    feraiseexcept (FE_INVALID);