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/*********************************************************** 
 *               The TULSA IBM C BOARD                     * 
 *                   918-664-8737                          * 
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#include "math.h" 
#include "errno.h" 
 
extern int errno; 
 
static double tansub(); 
 
double cotan(x) 
double x; 
{ 
        double y; 
 
        y = fabs(x); 
        if (y < 1.91e-152) { 
                errno = ERANGE; 
                if (x < 0.0) 
                        return -HUGE; 
                else 
                        return HUGE; 
        } 
        return tansub(x,y,2); 
} 
 
double tan(x) 
double x; 
{ 
        return tansub(x, fabs(x), 0); 
} 
 
#define P1 -0.13338350006421960681e+0 
#define P2 +0.34248878235890589960e-2 
#define P3 -0.17861707342254426711e-4 
#define Q0 +1.0 
#define Q1 -0.46671683339755294240e+0 
#define Q2 +0.25663832289440112864e-1 
#define Q3 -0.31181531907010027307e-3 
#define Q4 +0.49819433993786512270e-6 
 
#define P(f,g) (((P3*g P2)*g P1)*g*f + f) 
#define Q(g) ((((Q4*g Q3)*g Q2)*g Q1)*g Q0) 
 
#define YMAX 6.74652e09 
 
static double tansub(x, y, flag) 
double x,y; 
{ 
        double f, g, xn; 
        double xnum, xden; 
 
        if (y > YMAX) { 
                errno = ERANGE; 
                return 0.0; 
        } 
        if (modf(x*0.63661977236758134308, &xn) >= 0.5) 
                xn += (x < 0.0) ? -1.0 : 1.0; 
        f = (x - xn*1.57080078125) + xn*4.454455103380768678308e-6; 
        if (fabs(f) < 2.33e-10) { 
                xnum = f; 
                xden = 1.0; 
        } else { 
                g = f*f; 
                xnum = P(f,g); 
                xden = Q(g); 
        } 
        flag |= ((int)xn & 1); 
        switch (flag) { 
        case 1:         /* A: tan, xn odd */ 
                xnum = -xnum; 
        case 2:         /* B: cotan, xn even */ 
                return xden/xnum; 
 
        case 3:         /* C: cotan, xn odd */ 
                xnum = -xnum; 
        case 0:         /* D: tan, xn even */ 
                return xnum/xden; 
        } 
        return 0.0; 
}