Fix cacos (+Inf + finite*i) in round-downward mode (bug 16928).

According to C99/C11 Annex G, cacos applied to a value with real part
+Inf and finite imaginary part should produce a result with real part
+0.  glibc wrongly produces a result with real part -0 in FE_DOWNWARD
mode.  This patch fixes this by checking for zero results in the
relevant case of non-finite arguments (where there should never be a
result with -0 real part), and converts the tests of cacos to
ALL_RM_TEST.

Tested x86_64 and x86 and ulps updated accordingly.

	[BZ #16928]
	* math/s_cacos.c (__cacos): Ensure zero real part of result from
	non-finite arguments is +0.
	* math/s_cacosf.c (__cacosf): Likewise.
	* math/s_cacosl.c (__cacosl): Likewise.
	* math/libm-test.inc (cacos_test): Use ALL_RM_TEST.
	* sysdeps/i386/fpu/libm-test-ulps: Update.
	* sysdeps/x86_64/fpu/libm-test-ulps: Likewise.

1 files changed, 2 insertions, 0 deletions

diff --git a/math/s_cacosl.c b/math/s_cacosl.c
index b9d34930d6..8688d3cd36 100644
--- a/math/s_cacosl.c
+++ b/math/s_cacosl.c
@@ -34,6 +34,8 @@ __cacosl (__complex__ long double x)
       y = __casinl (x);
 
       __real__ res = M_PI_2l - __real__ y;
+      if (__real__ res == 0.0L)
+	__real__ res = 0.0L;
       __imag__ res = -__imag__ y;
     }
   else