2.11BSD#431 - /usr/src/usr.lib/libom/atan.c

   1: /*	@(#)atan.c	4.1	12/25/82	*/
   2: 
   3: 
   4: /*
   5: 	floating-point arctangent
   6: 
   7: 	atan returns the value of the arctangent of its
   8: 	argument in the range [-pi/2,pi/2].
   9: 
  10: 	atan2 returns the arctangent of arg1/arg2
  11: 	in the range [-pi,pi].
  12: 
  13: 	there are no error returns.
  14: 
  15: 	coefficients are #5077 from Hart & Cheney. (19.56D)
  16: */
  17: 
  18: 
  19: double static sq2p1  =2.414213562373095048802e0;
  20: static double sq2m1  = .414213562373095048802e0;
  21: static double pio2   =1.570796326794896619231e0;
  22: static double pio4   = .785398163397448309615e0;
  23: static double p4     = .161536412982230228262e2;
  24: static double p3     = .26842548195503973794141e3;
  25: static double p2     = .11530293515404850115428136e4;
  26: static double p1     = .178040631643319697105464587e4;
  27: static double p0     = .89678597403663861959987488e3;
  28: static double q4     = .5895697050844462222791e2;
  29: static double q3     = .536265374031215315104235e3;
  30: static double q2     = .16667838148816337184521798e4;
  31: static double q1     = .207933497444540981287275926e4;
  32: static double q0     = .89678597403663861962481162e3;
  33: 
  34: 
  35: /*
  36: 	atan makes its argument positive and
  37: 	calls the inner routine satan.
  38: */
  39: 
  40: double
  41: atan(arg)
  42: double arg;
  43: {
  44:     double satan();
  45: 
  46:     if(arg>0)
  47:         return(satan(arg));
  48:     else
  49:         return(-satan(-arg));
  50: }
  51: 
  52: 
  53: /*
  54: 	atan2 discovers what quadrant the angle
  55: 	is in and calls atan.
  56: */
  57: 
  58: double
  59: atan2(arg1,arg2)
  60: double arg1,arg2;
  61: {
  62:     double satan();
  63: 
  64:     if((arg1+arg2)==arg1)
  65:         if(arg1 >= 0.) return(pio2);
  66:         else return(-pio2);
  67:     else if(arg2 <0.)
  68:         if(arg1 >= 0.)
  69:             return(pio2+pio2 - satan(-arg1/arg2));
  70:         else
  71:             return(-pio2-pio2 + satan(arg1/arg2));
  72:     else if(arg1>0)
  73:         return(satan(arg1/arg2));
  74:     else
  75:         return(-satan(-arg1/arg2));
  76: }
  77: 
  78: /*
  79: 	satan reduces its argument (known to be positive)
  80: 	to the range [0,0.414...] and calls xatan.
  81: */
  82: 
  83: static double
  84: satan(arg)
  85: double arg;
  86: {
  87:     double  xatan();
  88: 
  89:     if(arg < sq2m1)
  90:         return(xatan(arg));
  91:     else if(arg > sq2p1)
  92:         return(pio2 - xatan(1.0/arg));
  93:     else
  94:         return(pio4 + xatan((arg-1.0)/(arg+1.0)));
  95: }
  96: 
  97: /*
  98: 	xatan evaluates a series valid in the
  99: 	range [-0.414...,+0.414...].
 100: */
 101: 
 102: static double
 103: xatan(arg)
 104: double arg;
 105: {
 106:     double argsq;
 107:     double value;
 108: 
 109:     argsq = arg*arg;
 110:     value = ((((p4*argsq + p3)*argsq + p2)*argsq + p1)*argsq + p0);
 111:     value = value/(((((argsq + q4)*argsq + q3)*argsq + q2)*argsq + q1)*argsq + q0);
 112:     return(value*arg);
 113: }

Defined functions

Defined variables