From d032e0d29b6ed9d3844916ada0ead19c3190ff9a Mon Sep 17 00:00:00 2001
From: Joseph Myers <joseph@codesourcery.com>
Date: Tue, 25 Sep 2012 19:43:49 +0000
Subject: Fix inaccuracy of clog, clog10 near |z| = 1 (bug 13629).

---
 math/s_clog.c | 13 +++++++++++++
 1 file changed, 13 insertions(+)

(limited to 'math/s_clog.c')

diff --git a/math/s_clog.c b/math/s_clog.c
index 2593066..79b1f37 100644
--- a/math/s_clog.c
+++ b/math/s_clog.c
@@ -85,6 +85,19 @@ __clog (__complex__ double x)
 	    d2m1 += absy * absy;
 	  __real__ result = __log1p (d2m1) / 2.0;
 	}
+      else if (absx < 1.0
+	       && absx >= 0.75
+	       && absy < DBL_EPSILON / 2.0
+	       && scale == 0)
+	{
+	  double d2m1 = (absx - 1.0) * (absx + 1.0);
+	  __real__ result = __log1p (d2m1) / 2.0;
+	}
+      else if (absx < 1.0 && (absx >= 0.75 || absy >= 0.5) && scale == 0)
+	{
+	  double d2m1 = __x2y2m1 (absx, absy);
+	  __real__ result = __log1p (d2m1) / 2.0;
+	}
       else
 	{
 	  double d = __ieee754_hypot (absx, absy);
-- 
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