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diff --git a/src/c/elementaryFunctions/log1p/slog1ps.c b/src/c/elementaryFunctions/log1p/slog1ps.c
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+++ b/src/c/elementaryFunctions/log1p/slog1ps.c
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+/*
+ *  Scilab ( http://www.scilab.org/ ) - This file is part of Scilab
+ *  Copyright (C) 2008-2008 - INRIA - Bruno JOFRET
+ *  Copyright (C) Bruno Pincon
+
+ *
+ *  This file must be used under the terms of the CeCILL.
+ *  This source file is licensed as described in the file COPYING, which
+ *  you should have received as part of this distribution.  The terms
+ *  are also available at
+ *  http://www.cecill.info/licences/Licence_CeCILL_V2-en.txt
+ *
+ */
+
+#include "log1p.h"
+#include "log.h"
+#include "lnp1m1.h"
+
+float		slog1ps(float in) {
+  static double A = -1.0/3.0;
+  static double B = 0.5;
+
+  if(in < -1)
+    {/* got NaN */
+      return (in - in) / (in - in); /* NaN */
+    }
+  else if(A <= in && in <= B)
+    {/* use the function log((1+g)/(1-g)) with g = x/(x + 2) */
+      return slnp1m1s(in / (in + 2));
+    }
+  else
+    {/* use the standard formula */
+      return slogs(in + 1);
+    }
+}