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

   1: /*
   2: 	floating point tangent
   3: 
   4: 	A series is used after range reduction.
   5: 	Coefficients are #4285 from Hart & Cheney. (19.74D)
   6: */
   7: 
   8: #include <errno.h>
   9: #include <math.h>
  10: 
  11: int errno;
  12: static double invpi   = 1.27323954473516268;
  13: static double p0     = -0.1306820264754825668269611177e+5;
  14: static double p1      = 0.1055970901714953193602353981e+4;
  15: static double p2     = -0.1550685653483266376941705728e+2;
  16: static double p3      = 0.3422554387241003435328470489e-1;
  17: static double p4      = 0.3386638642677172096076369e-4;
  18: static double q0     = -0.1663895238947119001851464661e+5;
  19: static double q1      = 0.4765751362916483698926655581e+4;
  20: static double q2     = -0.1555033164031709966900124574e+3;
  21: 
  22: double
  23: tan(arg)
  24: double arg;
  25: {
  26:     double modf();
  27:     double sign, temp, e, x, xsq;
  28:     int flag, i;
  29: 
  30:     flag = 0;
  31:     sign = 1.;
  32:     if(arg < 0.){
  33:         arg = -arg;
  34:         sign = -1.;
  35:     }
  36:     arg = arg*invpi;   /*overflow?*/
  37:     x = modf(arg,&e);
  38:     i = e;
  39:     switch(i%4) {
  40:     case 1:
  41:         x = 1. - x;
  42:         flag = 1;
  43:         break;
  44: 
  45:     case 2:
  46:         sign = - sign;
  47:         flag = 1;
  48:         break;
  49: 
  50:     case 3:
  51:         x = 1. - x;
  52:         sign = - sign;
  53:         break;
  54: 
  55:     case 0:
  56:         break;
  57:     }
  58: 
  59:     xsq = x*x;
  60:     temp = ((((p4*xsq+p3)*xsq+p2)*xsq+p1)*xsq+p0)*x;
  61:     temp = temp/(((1.0*xsq+q2)*xsq+q1)*xsq+q0);
  62: 
  63:     if(flag == 1) {
  64:         if(temp == 0.) {
  65:             errno = ERANGE;
  66:             if (sign>0)
  67:                 return(HUGE);
  68:             return(-HUGE);
  69:         }
  70:         temp = 1./temp;
  71:     }
  72:     return(sign*temp);
  73: }

Defined functions

Defined variables