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+
+/* @(#)z_atan2.c 1.0 98/08/13 */
+
+/*
+FUNCTION
+ <<atan2>>, <<atan2f>>---arc tangent of y/x
+
+INDEX
+ atan2
+INDEX
+ atan2f
+
+ANSI_SYNOPSIS
+ #include <math.h>
+ double atan2(double <[y]>,double <[x]>);
+ float atan2f(float <[y]>,float <[x]>);
+
+TRAD_SYNOPSIS
+ #include <math.h>
+ double atan2(<[y]>,<[x]>);
+ double <[y]>;
+ double <[x]>;
+
+ float atan2f(<[y]>,<[x]>);
+ float <[y]>;
+ float <[x]>;
+
+DESCRIPTION
+
+<<atan2>> computes the inverse tangent (arc tangent) of <[y]>/<[x]>.
+<<atan2>> produces the correct result even for angles near
+@ifinfo
+pi/2 or -pi/2
+@end ifinfo
+@tex
+$\pi/2$ or $-\pi/2$
+@end tex
+(that is, when <[x]> is near 0).
+
+<<atan2f>> is identical to <<atan2>>, save that it takes and returns
+<<float>>.
+
+RETURNS
+<<atan2>> and <<atan2f>> return a value in radians, in the range of
+@ifinfo
+-pi to pi.
+@end ifinfo
+@tex
+$-\pi$ to $\pi$.
+@end tex
+
+If both <[x]> and <[y]> are 0.0, <<atan2>> causes a <<DOMAIN>> error.
+
+You can modify error handling for these functions using <<matherr>>.
+
+PORTABILITY
+<<atan2>> is ANSI C. <<atan2f>> is an extension.
+
+
+*/
+
+/******************************************************************
+ * Arctangent2
+ *
+ * Input:
+ * v, u - floating point values
+ *
+ * Output:
+ * arctan2 of v / u
+ *
+ * Description:
+ * This routine returns the arctan2 of v / u.
+ *
+ *****************************************************************/
+
+#include "fdlibm.h"
+#include "zmath.h"
+
+#ifndef _DOUBLE_IS_32BITS
+
+double
+_DEFUN (atan2, (double, double),
+ double v _AND
+ double u)
+{
+ return (atangent (0.0, v, u, 1));
+}
+
+#endif /* _DOUBLE_IS_32BITS */