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usr.lib/libplot/hp2648/circle.c

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+/*
+ * Copyright (c) 1980 Regents of the University of California.
+ * All rights reserved.  The Berkeley software License Agreement
+ * specifies the terms and conditions for redistribution.
+ */
+
+#ifndef lint
+static char sccsid[] = "@(#)circle.c 1.1 94/10/31 SMI"; /* from UCB 5.1 5/7/85 */
+#endif not lint
+
+#include "hp2648.h"
+
+circle (xc,yc,r)
+int xc,yc,r;
+{
+	double costheta,sintheta,x,y,xn;
+	int xi,yi;
+
+	if(r<1){
+		point(xc,yc);
+		return;
+	}
+	sintheta = 1.0/r;
+	costheta = pow(1-sintheta*sintheta,0.5);
+	xi = x = r;
+	yi = y = 0;
+	do {
+		point(xc+xi,yc+yi);
+		xn = x;
+		xi = x = x*costheta + y*sintheta;
+		yi = y = y*costheta - xn*sintheta;
+	} while( ! (yi==0 && xi >= r-1));
+}