add fdlibm

git-svn-id: http://svn2.nishi.boats/svn/milsko/trunk@557 b9cfdab3-6d41-4d17-bbe4-086880011989

external/fdlibm/s_tanh.c

@@ -0,0 +1,73 @@
+
+/* @(#)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. 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"
+
+static const double one = 1.0, two = 2.0, tinyv = 1.0e-300;
+
+double tanh(double x) {
+	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; /* 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 - tinyv; /* raised inexact flag */
+	}
+	return (jx >= 0) ? z : -z;
+}