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/* tandg.c
*
* Circular tangent of argument in degrees
*
*
*
* SYNOPSIS:
*
* double x, y, tandg();
*
* y = tandg( x );
*
*
*
* DESCRIPTION:
*
* Returns the circular tangent of the argument x in degrees.
*
* Range reduction is modulo pi/4. A rational function
* x + x**3 P(x**2)/Q(x**2)
* is employed in the basic interval [0, pi/4].
*
*
*
* ACCURACY:
*
* Relative error:
* arithmetic domain # trials peak rms
* DEC 0,10 8000 3.4e-17 1.2e-17
* IEEE 0,10 30000 3.2e-16 8.4e-17
*
* ERROR MESSAGES:
*
* message condition value returned
* tandg total loss x > 8.0e14 (DEC) 0.0
* x > 1.0e14 (IEEE)
* tandg singularity x = 180 k + 90 MAXNUM
*/
/* cotdg.c
*
* Circular cotangent of argument in degrees
*
*
*
* SYNOPSIS:
*
* double x, y, cotdg();
*
* y = cotdg( x );
*
*
*
* DESCRIPTION:
*
* Returns the circular cotangent of the argument x in degrees.
*
* Range reduction is modulo pi/4. A rational function
* x + x**3 P(x**2)/Q(x**2)
* is employed in the basic interval [0, pi/4].
*
*
* ERROR MESSAGES:
*
* message condition value returned
* cotdg total loss x > 8.0e14 (DEC) 0.0
* x > 1.0e14 (IEEE)
* cotdg singularity x = 180 k MAXNUM
*/
/*
Cephes Math Library Release 2.0: April, 1987
Copyright 1984, 1987 by Stephen L. Moshier
Direct inquiries to 30 Frost Street, Cambridge, MA 02140
*/
#include "mconf.h"
#ifdef UNK
static double PI180 = 1.74532925199432957692E-2;
static double lossth = 1.0e14;
#endif
#ifdef DEC
static unsigned short P1[] = {0036616,0175065,0011224,0164711};
#define PI180 *(double *)P1
static double lossth = 8.0e14;
#endif
#ifdef IBMPC
static unsigned short P1[] = {0x9d39,0xa252,0xdf46,0x3f91};
#define PI180 *(double *)P1
static double lossth = 1.0e14;
#endif
#ifdef MIEEE
static unsigned short P1[] = {
0x3f91,0xdf46,0xa252,0x9d39
};
#define PI180 *(double *)P1
static double lossth = 1.0e14;
#endif
static double tancot(double, int);
extern double MAXNUM;
double
tandg(double x)
{
return( tancot(x,0) );
}
double
cotdg(double x)
{
return( tancot(x,1) );
}
static double
tancot(double xx, int cotflg)
{
double x;
int sign;
/* make argument positive but save the sign */
if( xx < 0 ) {
x = -xx;
sign = -1;
} else {
x = xx;
sign = 1;
}
if( x > lossth ) {
mtherr("tandg", TLOSS);
return 0.0;
}
/* modulo 180 */
x = x - 180.0*floor(x/180.0);
if (cotflg) {
if (x <= 90.0) {
x = 90.0 - x;
} else {
x = x - 90.0;
sign *= -1;
}
} else {
if (x > 90.0) {
x = 180.0 - x;
sign *= -1;
}
}
if (x == 0.0) {
return 0.0;
} else if (x == 45.0) {
return sign*1.0;
} else if (x == 90.0) {
mtherr( (cotflg ? "cotdg" : "tandg"), SING );
return MAXNUM;
}
/* x is now transformed into [0, 90) */
return sign * tan(x*PI180);
}
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