Fix inaccuracy of clog, clog10 near |z| = 1 (bug 13629).

1 files changed, 13 insertions, 0 deletions

diff --git a/math/s_clogl.c b/math/s_clogl.c
index eaba572ce7..af3ed99714 100644
--- a/math/s_clogl.c
+++ b/math/s_clogl.c
@@ -85,6 +85,19 @@ __clogl (__complex__ long double x)
 	    d2m1 += absy * absy;
 	  __real__ result = __log1pl (d2m1) / 2.0L;
 	}
+      else if (absx < 1.0L
+	       && absx >= 0.75L
+	       && absy < LDBL_EPSILON / 2.0L
+	       && scale == 0)
+	{
+	  long double d2m1 = (absx - 1.0L) * (absx + 1.0L);
+	  __real__ result = __log1pl (d2m1) / 2.0L;
+	}
+      else if (absx < 1.0L && (absx >= 0.75L || absy >= 0.5L) && scale == 0)
+	{
+	  long double d2m1 = __x2y2m1l (absx, absy);
+	  __real__ result = __log1pl (d2m1) / 2.0L;
+	}
       else
 	{
 	  long double d = __ieee754_hypotl (absx, absy);