Initial Contributionandroid-1.0release-1.0cdma-import

1 files changed, 82 insertions, 0 deletions

diff --git a/s_tanh.c b/s_tanh.c
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+
+/* @(#)s_tanh.c 1.3 95/01/18 */
+/*
+ * ====================================================
+ * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
+ *
+ * Developed at SunSoft, 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. ieee_tanh(x) is defined to be -----------
+ *				       x    -x
+ *				      e  + e
+ *	1. reduce x to non-negative by ieee_tanh(-x) = -ieee_tanh(x).
+ *	2.  0      <= x <= 2**-55 : ieee_tanh(x) := x*(one+x)
+ *					        -t
+ *	    2**-55 <  x <=  1     : ieee_tanh(x) := -----; t = ieee_expm1(-2x)
+ *					       t + 2
+ *						     2
+ *	    1      <= x <=  22.0  : ieee_tanh(x) := 1-  ----- ; t=ieee_expm1(2x)
+ *						   t + 2
+ *	    22.0   <  x <= INF    : ieee_tanh(x) := 1.
+ *
+ * Special cases:
+ *	tanh(NaN) is NaN;
+ *	only ieee_tanh(0)=0 is exact for finite argument.
+ */
+
+#include "fdlibm.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 ieee_tanh(double x)
+#else
+	double ieee_tanh(x)
+	double x;
+#endif
+{
+	double t,z;
+	int jx,ix;
+
+    /* High word of |x|. */
+	jx = __HI(x);
+	ix = jx&0x7fffffff;
+
+    /* x is INF or NaN */
+	if(ix>=0x7ff00000) { 
+	    if (jx>=0) return one/x+one;    /* ieee_tanh(+-inf)=+-1 */
+	    else       return one/x-one;    /* ieee_tanh(NaN) = NaN */
+	}
+
+    /* |x| < 22 */
+	if (ix < 0x40360000) {		/* |x|<22 */
+	    if (ix<0x3c800000) 		/* |x|<2**-55 */
+		return x*(one+x);    	/* ieee_tanh(small) = small */
+	    if (ix>=0x3ff00000) {	/* |x|>=1  */
+		t = ieee_expm1(two*ieee_fabs(x));
+		z = one - two/(t+two);
+	    } else {
+	        t = ieee_expm1(-two*ieee_fabs(x));
+	        z= -t/(t+two);
+	    }
+    /* |x| > 22, return +-1 */
+	} else {
+	    z = one - tiny;		/* raised inexact flag */
+	}
+	return (jx>=0)? z: -z;
+}