1 /* @(#)s_asinh.c 5.1 93/09/24 */
3 * ====================================================
4 * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
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
10 * ====================================================
12 * $FreeBSD: src/lib/msun/src/s_asinh.c,v 1.6 1999/08/28 00:06:43 peter Exp $
13 * $DragonFly: src/lib/msun/src/Attic/s_asinh.c,v 1.2 2003/06/17 04:26:53 dillon Exp $
19 * asinh(x) = sign(x) * log [ |x| + sqrt(x*x+1) ]
21 * asinh(x) := x if 1+x*x=1,
22 * := sign(x)*(log(x)+ln2)) for large |x|, else
23 * := sign(x)*log(2|x|+1/(|x|+sqrt(x*x+1))) if|x|>2, else
24 * := sign(x)*log1p(|x| + x^2/(1 + sqrt(1+x^2)))
28 #include "math_private.h"
35 one = 1.00000000000000000000e+00, /* 0x3FF00000, 0x00000000 */
36 ln2 = 6.93147180559945286227e-01, /* 0x3FE62E42, 0xFEFA39EF */
37 huge= 1.00000000000000000000e+300;
40 double asinh(double x)
50 if(ix>=0x7ff00000) return x+x; /* x is inf or NaN */
51 if(ix< 0x3e300000) { /* |x|<2**-28 */
52 if(huge+x>one) return x; /* return x inexact except 0 */
54 if(ix>0x41b00000) { /* |x| > 2**28 */
55 w = __ieee754_log(fabs(x))+ln2;
56 } else if (ix>0x40000000) { /* 2**28 > |x| > 2.0 */
58 w = __ieee754_log(2.0*t+one/(__ieee754_sqrt(x*x+one)+t));
59 } else { /* 2.0 > |x| > 2**-28 */
61 w =log1p(fabs(x)+t/(one+__ieee754_sqrt(one+t)));
63 if(hx>0) return w; else return -w;