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/*************************************************** 
 *        Exponential Routine                      * 
 *                                                 * 
 *        IBM PC "C" Language Board                * 
 *        Tulsa, OK 1918-664-8737                  * 
 *        SYSOP Lynn Long                          * 
 ***************************************************/ 
 
 
#include "math.h" 
#include "errno.h" 
 
#define P0 0.249999999999999993e+0 
#define P1 0.694360001511792852e-2 
#define P2 0.165203300268279130e-4 
#define Q0 0.500000000000000000e+0 
#define Q1 0.555538666969001188e-1 
#define Q2 0.495862884905441294e-3 
 
#define P(z) ((P2*z + P1)*z + P0) 
#define Q(z) ((Q2*z + Q1)*z + Q0) 
 
#define EPS     2.710505e-20 
 
double 
exp(x) 
double x; 
{ 
        int n; 
        double xn, g, r, z; 
        extern int errno; 
 
        if (x > LOGHUGE) { 
                errno = ERANGE; 
                return HUGE; 
        } 
        if (x < LOGTINY) { 
                errno = ERANGE; 
                return 0.0; 
        } 
        if (fabs(x) < EPS) 
                return 1.0; 
        n = z = x * 1.4426950408889634074; 
        if (n < 0) 
                --n; 
        if (z-n >= 0.5) 
                ++n; 
        xn = n; 
        g = ((x - xn*0.693359375)) + xn*2.1219444005469058277e-4; 
        z = g*g; 
        r = P(z)*g; 
        r = 0.5 + r/(Q(z)-r); 
        return ldexp(r,n+1); 
}