From d0419dbfbd19cb01398d43895a679c0bcb961070 Mon Sep 17 00:00:00 2001
From: Joseph Myers <joseph@codesourcery.com>
Date: Tue, 31 Jul 2012 14:21:19 +0000
Subject: Improve clog, clog10 handling of values with real or imaginary part
 slightly above 1 (bug 13629).

---
 math/s_clogl.c | 14 ++++++++++++++
 1 file changed, 14 insertions(+)

(limited to 'math/s_clogl.c')

diff --git a/math/s_clogl.c b/math/s_clogl.c
index d98a3c0..eaba572 100644
--- a/math/s_clogl.c
+++ b/math/s_clogl.c
@@ -22,6 +22,13 @@
 #include <math_private.h>
 #include <float.h>
 
+/* To avoid spurious underflows, use this definition to treat IBM long
+   double as approximating an IEEE-style format.  */
+#if LDBL_MANT_DIG == 106
+# undef LDBL_EPSILON
+# define LDBL_EPSILON 0x1p-106L
+#endif
+
 __complex__ long double
 __clogl (__complex__ long double x)
 {
@@ -71,6 +78,13 @@ __clogl (__complex__ long double x)
 	  else
 	    __real__ result = __log1pl (absy2) / 2.0L;
 	}
+      else if (absx > 1.0L && absx < 2.0L && absy < 1.0L && scale == 0)
+	{
+	  long double d2m1 = (absx - 1.0L) * (absx + 1.0L);
+	  if (absy >= LDBL_EPSILON)
+	    d2m1 += absy * absy;
+	  __real__ result = __log1pl (d2m1) / 2.0L;
+	}
       else
 	{
 	  long double d = __ieee754_hypotl (absx, absy);
-- 
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