n_atan.c revision 1.2 
1/*	$NetBSD: n_atan.c,v 1.2 1997/10/20 14:11:58 ragge Exp $	*/
2/*
3 * Copyright (c) 1985, 1993
4 *	The Regents of the University of California.  All rights reserved.
5 *
6 * Redistribution and use in source and binary forms, with or without
7 * modification, are permitted provided that the following conditions
8 * are met:
9 * 1. Redistributions of source code must retain the above copyright
10 *    notice, this list of conditions and the following disclaimer.
11 * 2. Redistributions in binary form must reproduce the above copyright
12 *    notice, this list of conditions and the following disclaimer in the
13 *    documentation and/or other materials provided with the distribution.
14 * 3. All advertising materials mentioning features or use of this software
15 *    must display the following acknowledgement:
16 *	This product includes software developed by the University of
17 *	California, Berkeley and its contributors.
18 * 4. Neither the name of the University nor the names of its contributors
19 *    may be used to endorse or promote products derived from this software
20 *    without specific prior written permission.
21 *
22 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
23 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
24 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
25 * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
26 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
27 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
28 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
29 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
30 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
31 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
32 * SUCH DAMAGE.
33 */
34
35#ifndef lint
36#if 0
37static char sccsid[] = "@(#)atan.c	8.1 (Berkeley) 6/4/93";
38#endif
39#endif /* not lint */
40
41/* ATAN(X)
42 * RETURNS ARC TANGENT OF X
43 * DOUBLE PRECISION (IEEE DOUBLE 53 bits, VAX D FORMAT 56 bits)
44 * CODED IN C BY K.C. NG, 4/16/85, REVISED ON 6/10/85.
45 *
46 * Required kernel function:
47 *	atan2(y,x)
48 *
49 * Method:
50 *	atan(x) = atan2(x,1.0).
51 *
52 * Special case:
53 *	if x is NaN, return x itself.
54 *
55 * Accuracy:
56 * 1)  If atan2() uses machine PI, then
57 *
58 *	atan(x) returns (PI/pi) * (the exact arc tangent of x) nearly rounded;
59 *	and PI is the exact pi rounded to machine precision (see atan2 for
60 *      details):
61 *
62 *	in decimal:
63 *		pi = 3.141592653589793 23846264338327 .....
64 *    53 bits   PI = 3.141592653589793 115997963 ..... ,
65 *    56 bits   PI = 3.141592653589793 227020265 ..... ,
66 *
67 *	in hexadecimal:
68 *		pi = 3.243F6A8885A308D313198A2E....
69 *    53 bits   PI = 3.243F6A8885A30  =  2 * 1.921FB54442D18	error=.276ulps
70 *    56 bits   PI = 3.243F6A8885A308 =  4 * .C90FDAA22168C2    error=.206ulps
71 *
72 *	In a test run with more than 200,000 random arguments on a VAX, the
73 *	maximum observed error in ulps (units in the last place) was
74 *	0.86 ulps.      (comparing against (PI/pi)*(exact atan(x))).
75 *
76 * 2)  If atan2() uses true pi, then
77 *
78 *	atan(x) returns the exact atan(x) with error below about 2 ulps.
79 *
80 *	In a test run with more than 1,024,000 random arguments on a VAX, the
81 *	maximum observed error in ulps (units in the last place) was
82 *	0.85 ulps.
83 */
84#include "mathimpl.h"
85
86double atan(x)
87double x;
88{
89	double one=1.0;
90	return(atan2(x,one));
91}
92