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diff --git a/lib/libm/noieee_src/n_csin.c b/lib/libm/noieee_src/n_csin.c
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+/*	$OpenBSD: n_csin.c,v 1.1 2008/10/07 22:25:53 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.
+ */
+
+/*							csin()
+ *
+ *	Complex circular sine
+ *
+ *
+ *
+ * SYNOPSIS:
+ *
+ * double complex csin();
+ * double complex z, w;
+ *
+ * w = csin (z);
+ *
+ *
+ *
+ * DESCRIPTION:
+ *
+ * If
+ *     z = x + iy,
+ *
+ * then
+ *
+ *     w = sin x  cosh y  +  i cos x sinh y.
+ *
+ * csin(z) = -i csinh(iz).
+ *
+ * ACCURACY:
+ *
+ *                      Relative error:
+ * arithmetic   domain     # trials      peak         rms
+ *    DEC       -10,+10      8400       5.3e-17     1.3e-17
+ *    IEEE      -10,+10     30000       3.8e-16     1.0e-16
+ * Also tested by csin(casin(z)) = z.
+ *
+ */
+
+#include <complex.h>
+#include <math.h>
+
+/* calculate cosh and sinh */
+
+static void
+cchsh(double x, double *c, double *s)
+{
+	double e, ei;
+
+	if (fabs(x) <= 0.5) {
+		*c = cosh(x);
+		*s = sinh(x);
+	}
+	else {
+		e = exp(x);
+		ei = 0.5/e;
+		e = 0.5 * e;
+		*s = e - ei;
+		*c = e + ei;
+	}
+}
+
+double complex
+csin(double complex z)
+{
+	double complex w;
+	double ch, sh;
+
+	cchsh( cimag (z), &ch, &sh );
+	w = sin (creal(z)) * ch + (cos (creal(z)) * sh) * I;
+	return (w);
+}