add directory gnu

gnu/glibc/glibc-1.03/math/bsd/common_source/tanh.c

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+/*
+ * Copyright (c) 1985 Regents of the University of California.
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms are permitted provided
+ * that: (1) source distributions retain this entire copyright notice and
+ * comment, and (2) distributions including binaries display the following
+ * acknowledgement:  ``This product includes software developed by the
+ * University of California, Berkeley and its contributors'' in the
+ * documentation or other materials provided with the distribution and in
+ * all advertising materials mentioning features or use of this software.
+ * Neither the name of the University nor the names of its contributors may
+ * be used to endorse or promote products derived from this software without
+ * specific prior written permission.
+ * THIS SOFTWARE IS PROVIDED ``AS IS'' AND WITHOUT ANY EXPRESS OR IMPLIED
+ * WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED WARRANTIES OF
+ * MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE.
+ */
+
+#ifndef lint
+static char sccsid[] = "@(#)tanh.c	5.5 (Berkeley) 10/9/90";
+#endif /* not lint */
+
+/* TANH(X)
+ * RETURN THE HYPERBOLIC TANGENT OF X
+ * DOUBLE PRECISION (VAX D FORMAT 56 BITS, IEEE DOUBLE 53 BITS)
+ * CODED IN C BY K.C. NG, 1/8/85; 
+ * REVISED BY K.C. NG on 2/8/85, 2/11/85, 3/7/85, 3/24/85.
+ *
+ * Required system supported functions :
+ *	copysign(x,y)
+ *	finite(x)
+ *
+ * Required kernel function:
+ *	expm1(x)	...exp(x)-1
+ *
+ * Method :
+ *	1. reduce x to non-negative by tanh(-x) = - tanh(x).
+ *	2.
+ *	    0      <  x <=  1.e-10 :  tanh(x) := x
+ *					          -expm1(-2x)
+ *	    1.e-10 <  x <=  1      :  tanh(x) := --------------
+ *					         expm1(-2x) + 2
+ *							  2
+ *	    1      <= x <=  22.0   :  tanh(x) := 1 -  ---------------
+ *						      expm1(2x) + 2
+ *	    22.0   <  x <= INF     :  tanh(x) := 1.
+ *
+ *	Note: 22 was chosen so that fl(1.0+2/(expm1(2*22)+2)) == 1.
+ *
+ * Special cases:
+ *	tanh(NaN) is NaN;
+ *	only tanh(0)=0 is exact for finite argument.
+ *
+ * Accuracy:
+ *	tanh(x) returns the exact hyperbolic tangent of x nealy rounded.
+ *	In a test run with 1,024,000 random arguments on a VAX, the maximum
+ *	observed error was 2.22 ulps (units in the last place).
+ */
+
+#include "mathimpl.h"
+
+double tanh(x)
+double x;
+{
+	static double one=1.0, two=2.0, small = 1.0e-10, big = 1.0e10;
+	double expm1(), t, copysign(), sign;
+	int finite();
+
+#if !defined(vax)&&!defined(tahoe)
+	if(x!=x) return(x);	/* x is NaN */
+#endif	/* !defined(vax)&&!defined(tahoe) */
+
+	sign=copysign(one,x);
+	x=copysign(x,one);
+	if(x < 22.0) 
+	    if( x > one )
+		return(copysign(one-two/(expm1(x+x)+two),sign));
+	    else if ( x > small )
+		{t= -expm1(-(x+x)); return(copysign(t/(two-t),sign));}
+	    else		/* raise the INEXACT flag for non-zero x */
+		{big+x; return(copysign(x,sign));}
+	else if(finite(x))
+	    return (sign+1.0E-37); /* raise the INEXACT flag */
+	else
+	    return(sign);	/* x is +- INF */
+}