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#include <math.h>
#include <errno.h>
/*
atan2 discovers what quadrant the angle
is in and calls atan.
*/
#define pio2 1.5707963267948966192313217
#define pi 3.1415926535897932384626434;
double
atan2(double arg1, double arg2)
{
if(arg1 == 0.0 && arg2 == 0.0){
errno = EDOM;
return 0.0;
}
if(arg1+arg2 == arg1) {
if(arg1 >= 0)
return pio2;
return -pio2;
}
arg1 = atan(arg1/arg2);
if(arg2 < 0) {
if(arg1 <= 0)
return arg1 + pi;
return arg1 - pi;
}
return arg1;
}
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