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Make cacosh (0 + iNaN) return NaN + i pi/2 (bug 22561, DR#471) [committed]

As per C11 DR#471 (adjusted resolution accepted for C17), cacosh (0 +
iNaN) should return NaN +/- i pi/2, not NaN + iNaN.

This patch fixes the code accordingly.  The test has hardcoded the
result with positive sign of the imaginary part (with an associated
comment), since the unspecified sign for a result other than 0 or
infinity isn't currently supported by the test infrastructure.

Tested for x86_64.  Committed.

2017-12-06  Joseph Myers  <>

	[BZ #22561]
	* math/s_cacosh_template.c (M_DECL_FUNC (__cacosh)): Use pi/2 for
	real part of result for argument 0 + i * NaN.
	* math/ (cacosh_test_data): Update expected
	results for tests of 0 + i * NaN.

diff --git a/math/ b/math/
index 518cb29..db700b9 100644
--- a/math/
+++ b/math/
@@ -46,8 +46,13 @@ static const struct test_c_c_data cacosh_test_data[] =
     TEST_c_c (cacosh, plus_infty, qnan_value, plus_infty, qnan_value),
     TEST_c_c (cacosh, minus_infty, qnan_value, plus_infty, qnan_value),
-    TEST_c_c (cacosh, 0, qnan_value, qnan_value, qnan_value),
-    TEST_c_c (cacosh, minus_zero, qnan_value, qnan_value, qnan_value),
+    /* The sign of the imaginary part of the result is unspecified
+       (see
+       <>),
+       but the libm-test infrastructure does not support describing
+       that.  */
+    TEST_c_c (cacosh, 0, qnan_value, qnan_value, lit_pi_2_d),
+    TEST_c_c (cacosh, minus_zero, qnan_value, qnan_value, lit_pi_2_d),
     TEST_c_c (cacosh, qnan_value, plus_infty, plus_infty, qnan_value),
     TEST_c_c (cacosh, qnan_value, minus_infty, plus_infty, qnan_value),
diff --git a/math/s_cacosh_template.c b/math/s_cacosh_template.c
index 14f0b2a..0014fd4 100644
--- a/math/s_cacosh_template.c
+++ b/math/s_cacosh_template.c
@@ -57,7 +57,10 @@ M_DECL_FUNC (__cacosh) (CFLOAT x)
 	  __real__ res = M_NAN;
-	  __imag__ res = M_NAN;
+	  if (rcls == FP_ZERO)
+	    __imag__ res = M_MLIT (M_PI_2);
+	  else
+	    __imag__ res = M_NAN;
   else if (rcls == FP_ZERO && icls == FP_ZERO)

Joseph S. Myers

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