73 lines
1.3 KiB
C
73 lines
1.3 KiB
C
/*
|
|
* (c) copyright 1988 by the Vrije Universiteit, Amsterdam, The Netherlands.
|
|
* See the copyright notice in the ACK home directory, in the file "Copyright".
|
|
*
|
|
* Author: Ceriel J.H. Jacobs
|
|
*/
|
|
|
|
/* $Id$ */
|
|
|
|
#define __NO_DEFS
|
|
#include <math.h>
|
|
|
|
#if __STDC__
|
|
#include <pc_math.h>
|
|
#endif
|
|
|
|
double
|
|
_atn(x)
|
|
double x;
|
|
{
|
|
/* Algorithm and coefficients from:
|
|
"Software manual for the elementary functions"
|
|
by W.J. Cody and W. Waite, Prentice-Hall, 1980
|
|
*/
|
|
|
|
static double p[] = {
|
|
-0.13688768894191926929e+2,
|
|
-0.20505855195861651981e+2,
|
|
-0.84946240351320683534e+1,
|
|
-0.83758299368150059274e+0
|
|
};
|
|
static double q[] = {
|
|
0.41066306682575781263e+2,
|
|
0.86157349597130242515e+2,
|
|
0.59578436142597344465e+2,
|
|
0.15024001160028576121e+2,
|
|
1.0
|
|
};
|
|
static double a[] = {
|
|
0.0,
|
|
0.52359877559829887307710723554658381, /* pi/6 */
|
|
M_PI_2,
|
|
1.04719755119659774615421446109316763 /* pi/3 */
|
|
};
|
|
|
|
int neg = x < 0;
|
|
int n;
|
|
double g;
|
|
|
|
if (neg) {
|
|
x = -x;
|
|
}
|
|
if (x > 1.0) {
|
|
x = 1.0/x;
|
|
n = 2;
|
|
}
|
|
else n = 0;
|
|
|
|
if (x > 0.26794919243112270647) { /* 2-sqtr(3) */
|
|
n = n + 1;
|
|
x = (((0.73205080756887729353*x-0.5)-0.5)+x)/
|
|
(1.73205080756887729353+x);
|
|
}
|
|
|
|
/* ??? avoid underflow ??? */
|
|
|
|
g = x * x;
|
|
x += x * g * POLYNOM3(g, p) / POLYNOM4(g, q);
|
|
if (n > 1) x = -x;
|
|
x += a[n];
|
|
return neg ? -x : x;
|
|
}
|