Original Version

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diff --git a/src/c/elementaryFunctions/acosh/zacoshs.c b/src/c/elementaryFunctions/acosh/zacoshs.c
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+++ b/src/c/elementaryFunctions/acosh/zacoshs.c
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+/*
+ *  Scilab ( http://www.scilab.org/ ) - This file is part of Scilab
+ *  Copyright (C) 2007-2008 - INRIA - Bruno JOFRET
+ *
+ *  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
+ *
+ */
+
+/*
+//  METHOD
+//     based on the formula :
+//
+//     acosh(z) = sign(-imag(acos(z)) i acos(z)
+//
+//	sign(x) =	1	if x >= 0
+//		|	-1	if x < 0
+*/
+
+#include "acosh.h"
+#include "acos.h"
+
+#define localSign(x) x >= 0 ? 1.0 : -1.0
+
+doubleComplex		zacoshs(doubleComplex z) {
+  doubleComplex acos_z = zacoss(z);
+  double sign = localSign(-zimags(acos_z));
+
+  return DoubleComplex(-sign * zimags(acos_z), sign * zreals(acos_z));
+}