1 files changed, 87 insertions, 0 deletions
diff --git a/sysdeps/libm-ieee754/s_tanh.c b/sysdeps/libm-ieee754/s_tanh.c
new file mode 100644
index 0000000..22d064b
--- /dev/null
+++ b/sysdeps/libm-ieee754/s_tanh.c
@@ -0,0 +1,87 @@
+/* @(#)s_tanh.c 5.1 93/09/24 */
+/*
+ * ====================================================
+ * 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.
+ * ====================================================
+ */
+
+#if defined(LIBM_SCCS) && !defined(lint)
+static char rcsid[] = "$NetBSD: s_tanh.c,v 1.7 1995/05/10 20:48:22 jtc Exp $";
+#endif
+
+/* 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**-55 : tanh(x) := x*(one+x)
+ *					        -t
+ *	    2**-55 <  x <=  1     : tanh(x) := -----; t = expm1(-2x)
+ *					       t + 2
+ *						     2
+ *	    1      <= x <=  22.0  : tanh(x) := 1-  ----- ; t=expm1(2x)
+ *						   t + 2
+ *	    22.0   <  x <= INF    : tanh(x) := 1.
+ *
+ * Special cases:
+ *	tanh(NaN) is NaN;
+ *	only tanh(0)=0 is exact for finite argument.
+ */
+
+#include "math.h"
+#include "math_private.h"
+
+#ifdef __STDC__
+static const double one=1.0, two=2.0, tiny = 1.0e-300;
+#else
+static double one=1.0, two=2.0, tiny = 1.0e-300;
+#endif
+
+#ifdef __STDC__
+	double __tanh(double x)
+#else
+	double __tanh(x)
+	double x;
+#endif
+{
+	double t,z;
+	int32_t jx,ix;
+
+    /* High word of |x|. */
+	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 */
+	}
+
+    /* |x| < 22 */
+	if (ix < 0x40360000) {		/* |x|<22 */
+	    if (ix<0x3c800000) 		/* |x|<2**-55 */
+		return x*(one+x);    	/* tanh(small) = small */
+	    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);
+	    }
+    /* |x| > 22, return +-1 */
+	} else {
+	    z = one - tiny;		/* raised inexact flag */
+	}
+	return (jx>=0)? z: -z;
+}
+weak_alias (__tanh, tanh)