74 lines
1.6 KiB
C
74 lines
1.6 KiB
C
/* $Header$ */
|
|
|
|
/*
|
|
floating-point arctangent
|
|
|
|
atan returns the value of the arctangent of its
|
|
argument in the range [-pi/2,pi/2].
|
|
|
|
there are no error returns.
|
|
|
|
coefficients are #5077 from Hart & Cheney. (19.56D)
|
|
*/
|
|
|
|
|
|
static double sq2p1 = 2.414213562373095048802e0;
|
|
static double sq2m1 = .414213562373095048802e0;
|
|
static double pio2 = 1.570796326794896619231e0;
|
|
static double pio4 = .785398163397448309615e0;
|
|
static double p4 = .161536412982230228262e2;
|
|
static double p3 = .26842548195503973794141e3;
|
|
static double p2 = .11530293515404850115428136e4;
|
|
static double p1 = .178040631643319697105464587e4;
|
|
static double p0 = .89678597403663861959987488e3;
|
|
static double q4 = .5895697050844462222791e2;
|
|
static double q3 = .536265374031215315104235e3;
|
|
static double q2 = .16667838148816337184521798e4;
|
|
static double q1 = .207933497444540981287275926e4;
|
|
static double q0 = .89678597403663861962481162e3;
|
|
|
|
/*
|
|
xatan evaluates a series valid in the
|
|
range [-0.414...,+0.414...].
|
|
*/
|
|
|
|
static double
|
|
xatan(arg)
|
|
double arg;
|
|
{
|
|
double argsq;
|
|
double value;
|
|
|
|
argsq = arg*arg;
|
|
value = ((((p4*argsq + p3)*argsq + p2)*argsq + p1)*argsq + p0);
|
|
value = value/(((((argsq + q4)*argsq + q3)*argsq + q2)*argsq + q1)*argsq + q0);
|
|
return(value*arg);
|
|
}
|
|
|
|
static double
|
|
satan(arg)
|
|
double arg;
|
|
{
|
|
if(arg < sq2m1)
|
|
return(xatan(arg));
|
|
else if(arg > sq2p1)
|
|
return(pio2 - xatan(1/arg));
|
|
else
|
|
return(pio4 + xatan((arg-1)/(arg+1)));
|
|
}
|
|
|
|
|
|
/*
|
|
atan makes its argument positive and
|
|
calls the inner routine satan.
|
|
*/
|
|
|
|
double
|
|
_atn(arg)
|
|
double arg;
|
|
{
|
|
if(arg>0)
|
|
return(satan(arg));
|
|
else
|
|
return(-satan(-arg));
|
|
}
|