4.3BSD - /usr/src/usr.lib/libom/log.c

   1: /*	@(#)log.c	4.2	1/22/85	*/
   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  = -.963769093377840513e1;
  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: }

Defined functions

Defined variables