1 files changed, 48 insertions, 2 deletions
diff --git a/src/elementaryFunctions/log/zlogs.c b/src/elementaryFunctions/log/zlogs.c
index 4b6dab26..dd0792a9 100644
--- a/src/elementaryFunctions/log/zlogs.c
+++ b/src/elementaryFunctions/log/zlogs.c
@@ -10,9 +10,55 @@
  *
  */
 
+#include <math.h>
 #include "log.h"
+#include "lapack.h"
+#include "log1p.h"
+#include "pythag.h"
 
 doubleComplex	zlogs(doubleComplex in) {
-  /* FIXME : Implementation */
-  return in;
+  static double sR2	= 1.41421356237309504;
+
+  double _RealIn = zreals(in);
+  double _ImgIn = zimags(in);
+
+  double _RealOut = 0;
+  double _ImgOut = 0;
+
+  double RMax = getOverflowThreshold();
+  double LInf = sqrt(getUnderflowThreshold());
+  double LSup = sqrt(0.5 * RMax);
+
+  double AbsReal = fabs(_RealIn);
+  double AbsImg	= fabs(_ImgIn);
+
+  _ImgOut = atan2(_ImgIn, _RealIn);
+
+  if(_ImgIn > _RealIn)
+    {/* switch Real part and Imaginary part */
+      double Temp	= AbsReal;
+      AbsReal		= AbsImg;
+      AbsImg		= Temp;
+    }
+
+  if((0.5 <= AbsReal) && (AbsReal <= sR2))
+    _RealOut = 0.5 * dlog1ps((AbsReal - 1) * (AbsReal + 1) + AbsImg * AbsImg);
+  else if(LInf < AbsImg && AbsReal < LSup)
+    _RealOut = 0.5 * dlogs(AbsReal * AbsReal + AbsImg * AbsImg);
+  else if(AbsReal > RMax)
+    _RealOut = AbsReal;
+  else
+    {
+      double Temp = dpythags(AbsReal, AbsImg);
+      if(Temp <= RMax)
+	{
+	  _RealOut = dlogs(Temp);
+	}
+      else /* handle rare spurious overflow with : */
+	{
+	  double Temp2 = AbsImg/AbsReal;
+	  _RealOut = dlogs(AbsReal) + 0.5 * dlog1ps(Temp2 * Temp2);
+	}
+    }
+  return DoubleComplex(_RealOut, _ImgOut);
 }