From da865e95bcf9a5365de78fa6b5c681aca0a1bb46 Mon Sep 17 00:00:00 2001
From: Joseph Myers <joseph@codesourcery.com>
Date: Thu, 26 Jul 2012 11:31:35 +0000
Subject: Improve clog, clog10 handling of values with real or imaginary part 1
 (bug 13629).

---
 math/s_clog.c | 36 +++++++++++++++++++++++++++---------
 1 file changed, 27 insertions(+), 9 deletions(-)

(limited to 'math/s_clog.c')

diff --git a/math/s_clog.c b/math/s_clog.c
index 2249e86b43..e28aa5157d 100644
--- a/math/s_clog.c
+++ b/math/s_clog.c
@@ -41,21 +41,21 @@ __clog (__complex__ double x)
     {
       /* Neither real nor imaginary part is NaN.  */
       double absx = fabs (__real__ x), absy = fabs (__imag__ x);
-      double d;
       int scale = 0;
 
+      if (absx < absy)
+	{
+	  double t = absx;
+	  absx = absy;
+	  absy = t;
+	}
+
       if (absx > DBL_MAX / 2.0)
 	{
 	  scale = -1;
 	  absx = __scalbn (absx, scale);
 	  absy = (absy >= DBL_MIN * 2.0 ? __scalbn (absy, scale) : 0.0);
 	}
-      else if (absy > DBL_MAX / 2.0)
-	{
-	  scale = -1;
-	  absx = (absx >= DBL_MIN * 2.0 ? __scalbn (absx, scale) : 0.0);
-	  absy = __scalbn (absy, scale);
-	}
       else if (absx < DBL_MIN && absy < DBL_MIN)
 	{
 	  scale = DBL_MANT_DIG;
@@ -63,9 +63,27 @@ __clog (__complex__ double x)
 	  absy = __scalbn (absy, scale);
 	}
 
-      d = __ieee754_hypot (absx, absy);
+      if (absx == 1.0 && scale == 0)
+	{
+	  double absy2 = absy * absy;
+	  if (absy2 <= DBL_MIN * 2.0)
+	    {
+#if __FLT_EVAL_METHOD__ == 0
+	      __real__ result = absy2 / 2.0 - absy2 * absy2 / 4.0;
+#else
+	      volatile double force_underflow = absy2 * absy2 / 4.0;
+	      __real__ result = absy2 / 2.0 - force_underflow;
+#endif
+	    }
+	  else
+	    __real__ result = __log1p (absy2) / 2.0;
+	}
+      else
+	{
+	  double d = __ieee754_hypot (absx, absy);
+	  __real__ result = __ieee754_log (d) - scale * M_LN2;
+	}
 
-      __real__ result = __ieee754_log (d) - scale * M_LN2;
       __imag__ result = __ieee754_atan2 (__imag__ x, __real__ x);
     }
   else
-- 
cgit 1.4.1