1 files changed, 73 insertions, 0 deletions
diff --git a/src/math/tanh.c b/src/math/tanh.c
new file mode 100644
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+++ b/src/math/tanh.c
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+/* origin: FreeBSD /usr/src/lib/msun/src/s_tanh.c */
+/*
+ * ====================================================
+ * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
+ *
+ * Developed at SunPro, a Sun Microsystems, Inc. business.
+ * Permission to use, copy, modify, and distribute this
+ * software is freely granted, provided that this notice
+ * is preserved.
+ * ====================================================
+ */
+/* Tanh(x)
+ * Return the Hyperbolic Tangent of x
+ *
+ * Method :
+ *                                     x    -x
+ *                                    e  - e
+ *      0. tanh(x) is defined to be -----------
+ *                                     x    -x
+ *                                    e  + e
+ *      1. reduce x to non-negative by tanh(-x) = -tanh(x).
+ *      2.  0      <= x <  2**-28 : tanh(x) := x with inexact if x != 0
+ *                                              -t
+ *          2**-28 <= x <  1      : tanh(x) := -----; t = expm1(-2x)
+ *                                             t + 2
+ *                                                   2
+ *          1      <= x <  22     : tanh(x) := 1 - -----; t = expm1(2x)
+ *                                                 t + 2
+ *          22     <= x <= INF    : tanh(x) := 1.
+ *
+ * Special cases:
+ *      tanh(NaN) is NaN;
+ *      only tanh(0)=0 is exact for finite argument.
+ */
+
+#include "libm.h"
+
+static const double one = 1.0, two = 2.0, tiny = 1.0e-300, huge = 1.0e300;
+
+double tanh(double x)
+{
+	double t,z;
+	int32_t jx,ix;
+
+	GET_HIGH_WORD(jx, x);
+	ix = jx & 0x7fffffff;
+
+	/* x is INF or NaN */
+	if (ix >= 0x7ff00000) {
+		if (jx >= 0)
+			return one/x + one;  /* tanh(+-inf)=+-1 */
+		else
+			return one/x - one;  /* tanh(NaN) = NaN */
+	}
+
+	if (ix < 0x40360000) {  /* |x| < 22 */
+		if (ix < 0x3e300000) {  /* |x| < 2**-28 */
+			/* tanh(tiny) = tiny with inexact */
+			if (huge+x > one)
+				return x;
+		}
+		if (ix >= 0x3ff00000) {  /* |x| >= 1  */
+			t = expm1(two*fabs(x));
+			z = one - two/(t+two);
+		} else {
+			t = expm1(-two*fabs(x));
+			z= -t/(t+two);
+		}
+	} else {  /* |x| >= 22, return +-1 */
+		z = one - tiny;  /* raise inexact */
+	}
+	return jx >= 0 ? z : -z;
+}