Fix clog10 (-0 +/- 0i) (bug 16362).

This patch fixes the imaginary part of clog10 (-0 +/- 0i), which
should be +/-pi / log(10) by analogy with clog (the functions were
wrongly returning a result with imaginary part +/-pi, same as for
clog, and the tests matched the incorrect result, though both
functions and tests were correct for the similar case of clog10 (-inf
+/- 0i)).  Tested x86_64 and x86.

	[BZ #16362]
	* math/s_clog10.c (M_PI_LOG10E): New macro.
	(__clog10): Use M_PI_LOG10E instead of M_PI when real and
	imaginary parts are 0.
	* math/s_clog10f.c (M_PI_LOG10Ef): New macro.
	(__clog10f): Use M_PI_LOG10Ef instead of M_PI when real and
	imaginary parts are 0.
	* math/s_clog10l.c (M_PI_LOG10El): New macro.
	(__clog10l): Use M_PI_LOG10El instead of M_PIl when real and
	imaginary parts are 0.
	* math/libm-test.inc (clog10_test_data): Update expected results
	for when real and imaginary parts are 0.

1 files changed, 4 insertions, 1 deletions

diff --git a/math/s_clog10.c b/math/s_clog10.c
index 417d56186c..e75787949f 100644
--- a/math/s_clog10.c
+++ b/math/s_clog10.c
@@ -25,6 +25,9 @@
 /* log_10 (2).  */
 #define M_LOG10_2 0.3010299956639811952137388947244930267682
 
+/* pi * log10 (e).  */
+#define M_PI_LOG10E 1.364376353841841347485783625431355770210
+
 __complex__ double
 __clog10 (__complex__ double x)
 {
@@ -35,7 +38,7 @@ __clog10 (__complex__ double x)
   if (__glibc_unlikely (rcls == FP_ZERO && icls == FP_ZERO))
     {
       /* Real and imaginary part are 0.0.  */
-      __imag__ result = signbit (__real__ x) ? M_PI : 0.0;
+      __imag__ result = signbit (__real__ x) ? M_PI_LOG10E : 0.0;
       __imag__ result = __copysign (__imag__ result, __imag__ x);
       /* Yes, the following line raises an exception.  */
       __real__ result = -1.0 / fabs (__real__ x);