Initial revision

lang/cem/libcc.ansi/math/atan2.c

@@ -0,0 +1,42 @@
+/*
+ * (c) copyright 1988 by the Vrije Universiteit, Amsterdam, The Netherlands.
+ * See the copyright notice in the ACK home directory, in the file "Copyright".
+ *
+ * Author: Ceriel J.H. Jacobs
+ */
+/* $Header$ */
+
+#include	<errno.h>
+#include	<math.h>
+#include	"localmath.h"
+
+double
+atan2(double y, double x)
+{
+	double absx, absy, val;
+
+	if (x == 0 && y == 0) {
+		errno = EDOM;
+		return 0;
+	}
+	absy = y < 0 ? -y : y;
+	absx = x < 0 ? -x : x;
+	if (absy - absx == absy) {
+		/* x negligible compared to y */
+		return y < 0 ? -M_PI_2 : M_PI_2;
+	}
+	if (absx - absy == absx) {
+		/* y negligible compared to x */
+		val = 0.0;
+	}
+	else	val = atan(y/x);
+	if (x > 0) {
+		/* first or fourth quadrant; already correct */
+		return val;
+	}
+	if (y < 0) {
+		/* third quadrant */
+		return val - M_PI;
+	}
+	return val + M_PI;
+}