1#include "FEATURE/uwin"
2
3#if !_UWIN || _lib_acosh
4
5void _STUB_acosh(){}
6
7#else
8
9/*
10 * Copyright (c) 1985, 1993
11 *	The Regents of the University of California.  All rights reserved.
12 *
13 * Redistribution and use in source and binary forms, with or without
14 * modification, are permitted provided that the following conditions
15 * are met:
16 * 1. Redistributions of source code must retain the above copyright
17 *    notice, this list of conditions and the following disclaimer.
18 * 2. Redistributions in binary form must reproduce the above copyright
19 *    notice, this list of conditions and the following disclaimer in the
20 *    documentation and/or other materials provided with the distribution.
21 * 3. Neither the name of the University nor the names of its contributors
22 *    may be used to endorse or promote products derived from this software
23 *    without specific prior written permission.
24 *
25 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
26 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
27 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
28 * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
29 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
30 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
31 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
32 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
33 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
34 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
35 * SUCH DAMAGE.
36 */
37
38#ifndef lint
39static char sccsid[] = "@(#)acosh.c	8.1 (Berkeley) 6/4/93";
40#endif /* not lint */
41
42/* ACOSH(X)
43 * RETURN THE INVERSE HYPERBOLIC COSINE OF X
44 * DOUBLE PRECISION (VAX D FORMAT 56 BITS, IEEE DOUBLE 53 BITS)
45 * CODED IN C BY K.C. NG, 2/16/85;
46 * REVISED BY K.C. NG on 3/6/85, 3/24/85, 4/16/85, 8/17/85.
47 *
48 * Required system supported functions :
49 *	sqrt(x)
50 *
51 * Required kernel function:
52 *	log1p(x) 		...return log(1+x)
53 *
54 * Method :
55 *	Based on
56 *		acosh(x) = log [ x + sqrt(x*x-1) ]
57 *	we have
58 *		acosh(x) := log1p(x)+ln2,	if (x > 1.0E20); else
59 *		acosh(x) := log1p( sqrt(x-1) * (sqrt(x-1) + sqrt(x+1)) ) .
60 *	These formulae avoid the over/underflow complication.
61 *
62 * Special cases:
63 *	acosh(x) is NaN with signal if x<1.
64 *	acosh(NaN) is NaN without signal.
65 *
66 * Accuracy:
67 *	acosh(x) returns the exact inverse hyperbolic cosine of x nearly
68 *	rounded. In a test run with 512,000 random arguments on a VAX, the
69 *	maximum observed error was 3.30 ulps (units of the last place) at
70 *	x=1.0070493753568216 .
71 *
72 * Constants:
73 * The hexadecimal values are the intended ones for the following constants.
74 * The decimal values may be used, provided that the compiler will convert
75 * from decimal to binary accurately enough to produce the hexadecimal values
76 * shown.
77 */
78
79#include "mathimpl.h"
80
81vc(ln2hi, 6.9314718055829871446E-1  ,7217,4031,0000,f7d0,   0, .B17217F7D00000)
82vc(ln2lo, 1.6465949582897081279E-12 ,bcd5,2ce7,d9cc,e4f1, -39, .E7BCD5E4F1D9CC)
83
84ic(ln2hi, 6.9314718036912381649E-1,  -1, 1.62E42FEE00000)
85ic(ln2lo, 1.9082149292705877000E-10,-33, 1.A39EF35793C76)
86
87#ifdef vccast
88#define    ln2hi    vccast(ln2hi)
89#define    ln2lo    vccast(ln2lo)
90#endif
91
92extern double acosh(x)
93double x;
94{
95	double t,big=1.E20; /* big+1==big */
96
97#if !defined(vax)&&!defined(tahoe)
98	if(x!=x) return(x);	/* x is NaN */
99#endif	/* !defined(vax)&&!defined(tahoe) */
100
101    /* return log1p(x) + log(2) if x is large */
102	if(x>big) {t=log1p(x)+ln2lo; return(t+ln2hi);}
103
104	t=sqrt(x-1.0);
105	return(log1p(t*(t+sqrt(x+1.0))));
106}
107
108#endif
109