73 lines
1.4 KiB
C
73 lines
1.4 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
|
|
*/
|
|
|
|
/* $Header$ */
|
|
|
|
#include <math.h>
|
|
#include <errno.h>
|
|
|
|
extern int errno;
|
|
extern double modf();
|
|
|
|
double
|
|
tan(x)
|
|
double x;
|
|
{
|
|
/* Algorithm and coefficients from:
|
|
"Software manual for the elementary functions"
|
|
by W.J. Cody and W. Waite, Prentice-Hall, 1980
|
|
*/
|
|
|
|
int negative = x < 0;
|
|
int invert = 0;
|
|
double y;
|
|
static double p[] = {
|
|
1.0,
|
|
-0.13338350006421960681e+0,
|
|
0.34248878235890589960e-2,
|
|
-0.17861707342254426711e-4
|
|
};
|
|
static double q[] = {
|
|
1.0,
|
|
-0.46671683339755294240e+0,
|
|
0.25663832289440112864e-1,
|
|
-0.31181531907010027307e-3,
|
|
0.49819433993786512270e-6
|
|
};
|
|
|
|
if (negative) x = -x;
|
|
|
|
/* ??? avoid loss of significance, error if x is too large ??? */
|
|
|
|
y = x * M_2_PI + 0.5;
|
|
|
|
/* Use extended precision to calculate reduced argument.
|
|
Here we used 12 bits of the mantissa for a1.
|
|
Also split x in integer part x1 and fraction part x2.
|
|
*/
|
|
#define A1 1.57080078125
|
|
#define A2 -4.454455103380768678308e-6
|
|
{
|
|
double x1, x2;
|
|
|
|
modf(y, &y);
|
|
if (modf(0.5*y, &x1)) invert = 1;
|
|
x2 = modf(x, &x1);
|
|
x = x1 - y * A1;
|
|
x += x2;
|
|
x -= y * A2;
|
|
#undef A1
|
|
#undef A2
|
|
}
|
|
|
|
/* ??? avoid underflow ??? */
|
|
y = x * x;
|
|
x += x * y * POLYNOM2(y, p+1);
|
|
y = POLYNOM4(y, q);
|
|
if (negative) x = -x;
|
|
return invert ? -y/x : x/y;
|
|
}
|