Subversion Repositories planix.SVN

/*
        exp returns the exponential function of its
        floating-point argument.

        The coefficients are #1069 from Hart and Cheney. (22.35D)
*/

#include <u.h>
#include <libc.h>

#define p0  .2080384346694663001443843411e7
#define p1  .3028697169744036299076048876e5
#define p2  .6061485330061080841615584556e2
#define q0  .6002720360238832528230907598e7
#define q1  .3277251518082914423057964422e6
#define q2  .1749287689093076403844945335e4
#define log2e  1.4426950408889634073599247
#define sqrt2  1.4142135623730950488016887
#define maxf  10000

double
exp(double arg)
{
        double fract, temp1, temp2, xsq;
        int ent;

        if(arg == 0)
                return 1;
        if(arg < -maxf)
                return 0;
        if(arg > maxf)
                return Inf(1);
        arg *= log2e;
        ent = floor(arg);
        fract = (arg-ent) - 0.5;
        xsq = fract*fract;
        temp1 = ((p2*xsq+p1)*xsq+p0)*fract;
        temp2 = ((xsq+q2)*xsq+q1)*xsq + q0;
        return ldexp(sqrt2*(temp2+temp1)/(temp2-temp1), ent);
}