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

   1: 
   2: /*
   3: 	floating-point arctangent
   4: 
   5: 	atan returns the value of the arctangent of its
   6: 	argument in the range [-pi/2,pi/2].
   7: 
   8: 	atan2 returns the arctangent of arg1/arg2
   9: 	in the range [-pi,pi].
  10: 
  11: 	there are no error returns.
  12: 
  13: 	coefficients are #5077 from Hart & Cheney. (19.56D)
  14: */
  15: 
  16: 
  17: double static sq2p1  =2.414213562373095048802e0;
  18: static double sq2m1  = .414213562373095048802e0;
  19: static double pio2   =1.570796326794896619231e0;
  20: static double pio4   = .785398163397448309615e0;
  21: static double p4     = .161536412982230228262e2;
  22: static double p3     = .26842548195503973794141e3;
  23: static double p2     = .11530293515404850115428136e4;
  24: static double p1     = .178040631643319697105464587e4;
  25: static double p0     = .89678597403663861959987488e3;
  26: static double q4     = .5895697050844462222791e2;
  27: static double q3     = .536265374031215315104235e3;
  28: static double q2     = .16667838148816337184521798e4;
  29: static double q1     = .207933497444540981287275926e4;
  30: static double q0     = .89678597403663861962481162e3;
  31: 
  32: 
  33: /*
  34: 	atan makes its argument positive and
  35: 	calls the inner routine satan.
  36: */
  37: 
  38: double
  39: atan(arg)
  40: double arg;
  41: {
  42:     double satan();
  43: 
  44:     if(arg>0)
  45:         return(satan(arg));
  46:     else
  47:         return(-satan(-arg));
  48: }
  49: 
  50: 
  51: /*
  52: 	atan2 discovers what quadrant the angle
  53: 	is in and calls atan.
  54: */
  55: 
  56: double
  57: atan2(arg1,arg2)
  58: double arg1,arg2;
  59: {
  60:     double satan();
  61: 
  62:     if((arg1+arg2)==arg1)
  63:         if(arg1 >= 0.) return(pio2);
  64:         else return(-pio2);
  65:     else if(arg2 <0.)
  66:         if(arg1 >= 0.)
  67:             return(pio2+pio2 - satan(-arg1/arg2));
  68:         else
  69:             return(-pio2-pio2 + satan(arg1/arg2));
  70:     else if(arg1>0)
  71:         return(satan(arg1/arg2));
  72:     else
  73:         return(-satan(-arg1/arg2));
  74: }
  75: 
  76: /*
  77: 	satan reduces its argument (known to be positive)
  78: 	to the range [0,0.414...] and calls xatan.
  79: */
  80: 
  81: static double
  82: satan(arg)
  83: double arg;
  84: {
  85:     double  xatan();
  86: 
  87:     if(arg < sq2m1)
  88:         return(xatan(arg));
  89:     else if(arg > sq2p1)
  90:         return(pio2 - xatan(1.0/arg));
  91:     else
  92:         return(pio4 + xatan((arg-1.0)/(arg+1.0)));
  93: }
  94: 
  95: /*
  96: 	xatan evaluates a series valid in the
  97: 	range [-0.414...,+0.414...].
  98: */
  99: 
 100: static double
 101: xatan(arg)
 102: double arg;
 103: {
 104:     double argsq;
 105:     double value;
 106: 
 107:     argsq = arg*arg;
 108:     value = ((((p4*argsq + p3)*argsq + p2)*argsq + p1)*argsq + p0);
 109:     value = value/(((((argsq + q4)*argsq + q3)*argsq + q2)*argsq + q1)*argsq + q0);
 110:     return(value*arg);
 111: }

Defined functions

Defined variables