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

1 files changed, 13 insertions, 0 deletions

diff --git a/math/s_clogf.c b/math/s_clogf.c
index 92f782c47b..2b9038b411 100644
--- a/math/s_clogf.c
+++ b/math/s_clogf.c
@@ -85,6 +85,19 @@ __clogf (__complex__ float x)
 	    d2m1 += absy * absy;
 	  __real__ result = __log1pf (d2m1) / 2.0f;
 	}
+      else if (absx < 1.0f
+	       && absx >= 0.75f
+	       && absy < FLT_EPSILON / 2.0f
+	       && scale == 0)
+	{
+	  float d2m1 = (absx - 1.0f) * (absx + 1.0f);
+	  __real__ result = __log1pf (d2m1) / 2.0f;
+	}
+      else if (absx < 1.0f && (absx >= 0.75f || absy >= 0.5f) && scale == 0)
+	{
+	  float d2m1 = __x2y2m1f (absx, absy);
+	  __real__ result = __log1pf (d2m1) / 2.0f;
+	}
       else
 	{
 	  float d = __ieee754_hypotf (absx, absy);