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

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.

	[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/libm-test-cacosh.inc (cacosh_test_data): Update expected
	results for tests of 0 + i * NaN.

diff --git a/ChangeLog b/ChangeLog
index 9a57c30..b81d994 100644 (file)
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,11 @@
+2017-12-06  Joseph Myers  <joseph@codesourcery.com>
+
+       [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/libm-test-cacosh.inc (cacosh_test_data): Update expected
+       results for tests of 0 + i * NaN.
+
 2017-12-06  Adhemerval Zanella  <adhemerval.zanella@linaro.org>
 
        * sysdeps/alpha/fpu/libm-test-ulps: Update.

diff --git a/math/libm-test-cacosh.inc b/math/libm-test-cacosh.inc
index 518cb29..db700b9 100644 (file)
--- a/math/libm-test-cacosh.inc
+++ b/math/libm-test-cacosh.inc
@@ -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
+       <http://www.open-std.org/jtc1/sc22/wg14/www/docs/n2173.htm>),
+       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 (file)
--- a/math/s_cacosh_template.c
+++ b/math/s_cacosh_template.c
@@ -57,7 +57,10 @@ M_DECL_FUNC (__cacosh) (CFLOAT x)
       else
        {
          __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)