2.9BSD - /usr/src/lib/m/log.c

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

Defined functions

Defined variables