79 lines
1.5 KiB
C
79 lines
1.5 KiB
C
|
/*
|
||
|
|
floating-point arctangent
|
||
|
|
|
||
|
|
atan returns the value of the arctangent of its
|
||
|
|
argument in the range [-pi/2,pi/2].
|
||
|
|
|
||
|
|
atan2 returns the arctangent of arg1/arg2
|
||
|
|
in the range [-pi,pi].
|
||
|
|
|
||
|
|
there are no error returns.
|
||
|
|
|
||
|
|
coefficients are #5077 from Hart & Cheney. (19.56D)
|
||
|
|
*/
|
||
|
|
|
||
|
|
#include <u.h>
|
||
|
|
#include <libc.h>
|
||
|
|
|
||
|
|
#define sq2p1 2.414213562373095048802e0
|
||
|
|
#define sq2m1 .414213562373095048802e0
|
||
|
|
#define p4 .161536412982230228262e2
|
||
|
|
#define p3 .26842548195503973794141e3
|
||
|
|
#define p2 .11530293515404850115428136e4
|
||
|
|
#define p1 .178040631643319697105464587e4
|
||
|
|
#define p0 .89678597403663861959987488e3
|
||
|
|
#define q4 .5895697050844462222791e2
|
||
|
|
#define q3 .536265374031215315104235e3
|
||
|
|
#define q2 .16667838148816337184521798e4
|
||
|
|
#define q1 .207933497444540981287275926e4
|
||
|
|
#define q0 .89678597403663861962481162e3
|
||
|
|
|
||
|
|
|
||
|
|
/*
|
||
|
|
xatan evaluates a series valid in the
|
||
|
|
range [-0.414...,+0.414...]. (tan(pi/8))
|
||
|
|
*/
|
||
|
|
|
||
|
|
static
|
||
|
|
double
|
||
|
|
xatan(double arg)
|
||
|
|
{
|
||
|
|
double argsq, 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;
|
||
|
|
}
|
||
|
|
|
||
|
|
/*
|
||
|
|
satan reduces its argument (known to be positive)
|
||
|
|
to the range [0,0.414...] and calls xatan.
|
||
|
|
*/
|
||
|
|
|
||
|
|
static
|
||
|
|
double
|
||
|
|
satan(double arg)
|
||
|
|
{
|
||
|
|
|
||
|
|
if(arg < sq2m1)
|
||
|
|
return xatan(arg);
|
||
|
|
if(arg > sq2p1)
|
||
|
|
return PIO2 - xatan(1/arg);
|
||
|
|
return PIO2/2 + xatan((arg-1)/(arg+1));
|
||
|
|
}
|
||
|
|
|
||
|
|
/*
|
||
|
|
atan makes its argument positive and
|
||
|
|
calls the inner routine satan.
|
||
|
|
*/
|
||
|
|
|
||
|
|
double
|
||
|
|
atan(double arg)
|
||
|
|
{
|
||
|
|
|
||
|
|
if(arg > 0)
|
||
|
|
return satan(arg);
|
||
|
|
return -satan(-arg);
|
||
|
|
}
|