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

1.1     ! root        1: /*     @(#)log.c       4.1     12/25/82        */
        !             2: 
        !             3: /*
        !             4:        log returns the natural logarithm of its floating
        !             5:        point argument.
        !             6: 
        !             7:        The coefficients are #2705 from Hart & Cheney. (19.38D)
        !             8: 
        !             9:        It calls frexp.
        !            10: */
        !            11: 
        !            12: #include <errno.h>
        !            13: #include <math.h>
        !            14: 
        !            15: int    errno;
        !            16: double frexp();
        !            17: static double  log2    = 0.693147180559945309e0;
        !            18: static double  ln10    = 2.302585092994045684;
        !            19: static double  sqrto2  = 0.707106781186547524e0;
        !            20: static double  p0      = -.240139179559210510e2;
        !            21: static double  p1      = 0.309572928215376501e2;
        !            22: static double  p2      = -.963769093368686593e1;
        !            23: static double  p3      = 0.421087371217979714e0;
        !            24: static double  q0      = -.120069589779605255e2;
        !            25: static double  q1      = 0.194809660700889731e2;
        !            26: static double  q2      = -.891110902798312337e1;
        !            27: 
        !            28: double
        !            29: log(arg)
        !            30: double arg;
        !            31: {
        !            32:        double x,z, zsq, temp;
        !            33:        int exp;
        !            34: 
        !            35:        if(arg <= 0.) {
        !            36:                errno = EDOM;
        !            37:                return(-HUGE);
        !            38:        }
        !            39:        x = frexp(arg,&exp);
        !            40:        while(x<0.5) {
        !            41:                x = x*2;
        !            42:                exp = exp-1;
        !            43:        }
        !            44:        if(x<sqrto2) {
        !            45:                x = 2*x;
        !            46:                exp = exp-1;
        !            47:        }
        !            48: 
        !            49:        z = (x-1)/(x+1);
        !            50:        zsq = z*z;
        !            51: 
        !            52:        temp = ((p3*zsq + p2)*zsq + p1)*zsq + p0;
        !            53:        temp = temp/(((1.0*zsq + q2)*zsq + q1)*zsq + q0);
        !            54:        temp = temp*z + exp*log2;
        !            55:        return(temp);
        !            56: }
        !            57: 
        !            58: double
        !            59: log10(arg)
        !            60: double arg;
        !            61: {
        !            62: 
        !            63:        return(log(arg)/ln10);
        !            64: }

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