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#include "compat.h"
#if ! HAVE_ATAN2
# include <stdio.h>
# include <math.h>
# ifndef M_PI
# define M_PI 3.1415926535898
# endif
double
atan2(double y, double x)
{
double result;
/* return a value between -PI and PI */
if (x*x + y*y == 0) {
fprintf(stderr, _("Sorry, the value atan2(0, 0) is indeterminate.\n"));
exit(EXIT_FAILURE);
}
if (x == 0) return (y > 0) ? M_PI / 2: -M_PI / 2;
result = atan(y / x);
/* if atan() returns a result in the 2nd quadrant, put it into 4th quadrant */
if (result > M_PI / 2) result -= M_PI;
if (x > 0) return result; /* should be in range -PI/2, PI/2 */
else {
if (y > 0) return result + M_PI;
else return result - M_PI;
}
}
#endif
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