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Annotation of 42BSD/usr.lib/libm/exp.c, revision 1.1

1.1     ! root        1: /*     @(#)exp.c       4.1     12/25/82        */
        !             2: 
        !             3: /*
        !             4:        exp returns the exponential function of its
        !             5:        floating-point argument.
        !             6: 
        !             7:        The coefficients are #1069 from Hart and Cheney. (22.35D)
        !             8: */
        !             9: 
        !            10: #include <errno.h>
        !            11: #include <math.h>
        !            12: 
        !            13: int    errno;
        !            14: static double  p0      = .2080384346694663001443843411e7;
        !            15: static double  p1      = .3028697169744036299076048876e5;
        !            16: static double  p2      = .6061485330061080841615584556e2;
        !            17: static double  q0      = .6002720360238832528230907598e7;
        !            18: static double  q1      = .3277251518082914423057964422e6;
        !            19: static double  q2      = .1749287689093076403844945335e4;
        !            20: static double  log2e   = 1.4426950408889634073599247;
        !            21: static double  sqrt2   = 1.4142135623730950488016887;
        !            22: static double  maxf    = 10000;
        !            23: 
        !            24: double
        !            25: exp(arg)
        !            26: double arg;
        !            27: {
        !            28:        double fract;
        !            29:        double temp1, temp2, xsq;
        !            30:        int ent;
        !            31: 
        !            32:        if(arg == 0.)
        !            33:                return(1.);
        !            34:        if(arg < -maxf)
        !            35:                return(0.);
        !            36:        if(arg > maxf) {
        !            37:                errno = ERANGE;
        !            38:                return(HUGE);
        !            39:        }
        !            40:        arg *= log2e;
        !            41:        ent = floor(arg);
        !            42:        fract = (arg-ent) - 0.5;
        !            43:        xsq = fract*fract;
        !            44:        temp1 = ((p2*xsq+p1)*xsq+p0)*fract;
        !            45:        temp2 = ((1.0*xsq+q2)*xsq+q1)*xsq + q0;
        !            46:        return(ldexp(sqrt2*(temp2+temp1)/(temp2-temp1), ent));
        !            47: }

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