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diff --git a/lib/libm/src/s_ctanh.c b/lib/libm/src/s_ctanh.c
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+/*	$OpenBSD: s_ctanh.c,v 1.1 2008/09/07 20:36:09 martynas Exp $	*/
+/*
+ * Copyright (c) 2008 Stephen L. Moshier <steve@moshier.net>
+ *
+ * Permission to use, copy, modify, and distribute this software for any
+ * purpose with or without fee is hereby granted, provided that the above
+ * copyright notice and this permission notice appear in all copies.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+ * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
+ * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
+ * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+ * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
+ * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
+ * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+ */
+
+/*							ctanh
+ *
+ *	Complex hyperbolic tangent
+ *
+ *
+ *
+ * SYNOPSIS:
+ *
+ * double complex ctanh();
+ * double complex z, w;
+ *
+ * w = ctanh (z);
+ *
+ *
+ *
+ * DESCRIPTION:
+ *
+ * tanh z = (sinh 2x  +  i sin 2y) / (cosh 2x + cos 2y) .
+ *
+ * ACCURACY:
+ *
+ *                      Relative error:
+ * arithmetic   domain     # trials      peak         rms
+ *    IEEE      -10,+10     30000       1.7e-14     2.4e-16
+ *
+ */
+
+#include <complex.h>
+#include <math.h>
+
+double complex
+ctanh(double complex z)
+{
+	double complex w;
+	double x, y, d;
+
+	x = creal(z);
+	y = cimag(z);
+	d = cosh (2.0 * x) + cos (2.0 * y);
+	w = sinh (2.0 * x) / d  +  (sin (2.0 * y) / d) * I;
+	return (w);
+}