Improve clog, clog10 handling of values with real or imaginary part 1 (bug 13629).

1 files changed, 27 insertions, 9 deletions

diff --git a/math/s_clog10.c b/math/s_clog10.c
index cf5fb8a0b5..b733b048b9 100644
--- a/math/s_clog10.c
+++ b/math/s_clog10.c
@@ -44,21 +44,21 @@ __clog10 (__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;
@@ -66,9 +66,27 @@ __clog10 (__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 * M_LN10)
+	    {
+#if __FLT_EVAL_METHOD__ == 0
+	      __real__ result = (absy2 / 2.0 - absy2 * absy2 / 4.0) * M_LOG10E;
+#else
+	      volatile double force_underflow = absy2 * absy2 / 4.0;
+	      __real__ result = (absy2 / 2.0 - force_underflow) * M_LOG10E;
+#endif
+	    }
+	  else
+	    __real__ result = __log1p (absy2) * (M_LOG10E / 2.0);
+	}
+      else
+	{
+	  double d = __ieee754_hypot (absx, absy);
+	  __real__ result = __ieee754_log10 (d) - scale * M_LOG10_2;
+	}
 
-      __real__ result = __ieee754_log10 (d) - scale * M_LOG10_2;
       __imag__ result = M_LOG10E * __ieee754_atan2 (__imag__ x, __real__ x);
     }
   else