s_asinhl.c revision 23579 
1/* @(#)s_asinh.c 5.1 93/09/24 */
2/*
3 * ====================================================
4 * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
5 *
6 * Developed at SunPro, a Sun Microsystems, Inc. business.
7 * Permission to use, copy, modify, and distribute this
8 * software is freely granted, provided that this notice
9 * is preserved.
10 * ====================================================
11 */
12
13#ifndef lint
14static char rcsid[] = "$Id: s_asinh.c,v 1.4 1997/02/22 15:10:56 peter Exp $";
15#endif
16
17/* asinh(x)
18 * Method :
19 *	Based on
20 *		asinh(x) = sign(x) * log [ |x| + sqrt(x*x+1) ]
21 *	we have
22 *	asinh(x) := x  if  1+x*x=1,
23 *		 := sign(x)*(log(x)+ln2)) for large |x|, else
24 *		 := sign(x)*log(2|x|+1/(|x|+sqrt(x*x+1))) if|x|>2, else
25 *		 := sign(x)*log1p(|x| + x^2/(1 + sqrt(1+x^2)))
26 */
27
28#include "math.h"
29#include "math_private.h"
30
31#ifdef __STDC__
32static const double
33#else
34static double
35#endif
36one =  1.00000000000000000000e+00, /* 0x3FF00000, 0x00000000 */
37ln2 =  6.93147180559945286227e-01, /* 0x3FE62E42, 0xFEFA39EF */
38huge=  1.00000000000000000000e+300;
39
40#ifdef __STDC__
41	double asinh(double x)
42#else
43	double asinh(x)
44	double x;
45#endif
46{
47	double t,w;
48	int32_t hx,ix;
49	GET_HIGH_WORD(hx,x);
50	ix = hx&0x7fffffff;
51	if(ix>=0x7ff00000) return x+x;	/* x is inf or NaN */
52	if(ix< 0x3e300000) {	/* |x|<2**-28 */
53	    if(huge+x>one) return x;	/* return x inexact except 0 */
54	}
55	if(ix>0x41b00000) {	/* |x| > 2**28 */
56	    w = __ieee754_log(fabs(x))+ln2;
57	} else if (ix>0x40000000) {	/* 2**28 > |x| > 2.0 */
58	    t = fabs(x);
59	    w = __ieee754_log(2.0*t+one/(__ieee754_sqrt(x*x+one)+t));
60	} else {		/* 2.0 > |x| > 2**-28 */
61	    t = x*x;
62	    w =log1p(fabs(x)+t/(one+__ieee754_sqrt(one+t)));
63	}
64	if(hx>0) return w; else return -w;
65}
66